RT8206A B

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RT8206A - RT8206A

RT8206A/B
High-Efficiency, Main Power Supply Controllers Notebook Computers
RT8206A/B dual step-down, switch-mode powersupply (SMPS) controller generates logic-supply voltages battery-powered systems. RT8206A/B includes pulse-width modulation (PWM) controllers fixed 3.3V adjustable from 5.5V. optional external charge pump monitored through SECFB (RT8206A). This device also features linear regulator providing fixed output. linear regulator provides 70mA output current with automatic linear-regulator bootstrapping input. RT8206A/B includes on-board power-up sequencing, power-good outputs, internal soft-start, internal soft-discharge output that prevents negative voltages shutdown. constant on-time control scheme operates without sense resistors provides 100ns response load transients while maintaining relatively constant switching frequency. unique ultrasonic mode maintains switching frequency above 25kHz, which eliminates noise audio applications. Other features include diodeemulation mode (DEM), which maximizes efficiency light-load applications, fixed-frequency mode, which reduces interference sensitive application. RT8206A/B available WQFN-32L package.
Features
Wide Input Voltage Range Dual Fixed 5V/3.3V Outputs Adjustable from 5.5V, 1.5% Accuracy Secondary Feedback Input Maintains Charge Pump Voltage (RT8206A) Independent Enable Power Good Fixed Output 70mA Reference Voltage 50uA Constant ON-Time Control with 100ns Load Step Response Frequency Selectable Setting RDS(ON) Current Sensing Programmable Current Limit Selectable PWM, Ultrasonic Mode Internal Soft-Start with Steps Current Limiting Soft-Discharge High Efficiency Quiescent Power Dissipation Thermal Shutdown RoHS Compliant Halogen Free
Ordering Information
RT8206 Package Type WQFN-32L (W-Type) Operating Temperature Range Green (Halogen Free with Commercial Standard) With SECFB Without SECFB
Note Richtek Green products RoHS compliant compatible with current requirements IPC/JEDEC J-STD-020. Suitable SnPb Pb-free soldering processes.
Applications
Notebook Sub-Notebook Computers 3-Cell 4-Cell Battery-Powered Devices
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RT8206A/B
Configurations
(TOP VIEW)
PGOOD2 PGOOD2 UGATE2 UGATE2
PHASE2
ENLDO
BOOT2 LGATE2 PGND SECFB PVCC LGATE1 BOOT1
ENLDO
PHASE2
VOUT2
VOUT2
ILIM2
ILIM2
SKIP
SKIP
BOOT2 LGATE2 PGND PVCC LGATE1 BOOT1
PHASE1
PGOOD1
PGOOD1
UGATE1
WQFN-32L RT8206A
WQFN-32L RT8206B
Typical Application Circuit
10µF 0.1µF
RT8206A/B UGATE2 BOOT2 UGATE1 BOOT1
0.1µF
10µF
UGATE1
PHASE1
10µF
VOUT1
ILIM1
VOUT1
ILIM1
PHASE2 LGATE2 PGND VOUT2 PGOOD1
4.7µH
VOUT2 3.3V 220µF
VOUT1 220µF
6.8µH 0.1µF 0.1µF 200k
0.1µF
PHASE1 LGATE1
0.22µF
100k 100k
0.1µF 0.1µF
VOUT1
PVCC PVCC
PGOOD2
ENLDO ILIM1
Enable 3.3V Enable Control 180k 180k Frequency Control PWM/DEM/Ultrasonic
SECFB/NC
PVCC
ILIM2
SKIP
4.7µF
Exposed (33)
Figure Fixed Voltage Regulator
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RT8206A/B
10µF 0.1µF
RT8206A/B UGATE2 BOOT2 UGATE1 BOOT1
0.1µF
10µF
10µF
PHASE2 LGATE2 PGND VOUT2 PGOOD1
4.7µH
VOUT1 220µF
6.8µH 0.1µF 0.1µF
0.1µF
11.5k PVCC PVCC
220µF
VOUT2 3.3V
PHASE1 LGATE1
0.1µF
0.1µF 0.1µF
VOUT1
0.22µF
100k 100k
PGOOD2 ENLDO
Enable 3.3V Enable Control
180k 180k
200k
SECFB/NC
ILIM1 ILIM2
0.1µF
4.7µF
PVCC
SKIP
Frequency Control PWM/DEM/Ultrasonic
Exposed (33)
Figure Adjustable Voltage Regulator
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RT8206A/B
Function Block Diagram
SKIP BOOT1 UGATE1 PHASE1 SMPS1 Buck Controller SMPS2 Buck Controller BOOT2 UGATE2 PHASE2
LGATE1 PGND VOUT1 ILIM1 PGOOD1
LGATE2 VOUT2 ILIM2 PGOOD2
Threshold Internal Logic Power-On Sequence Clear Fault Latch PVCC ENLDO
Thermal Shutdown
Function Block Diagram
UGATE VOUT On-Time Compute 1-Shot TRIG
TRIG 1-Shot
Comp
LGATE Over-Voltage Fault Latch Under-Voltage
Blanking Time
ILIM
Time 25kHz Detector Zero Detector
Current Limit
PGOOD
PHASE
SKIP
Controller (One Side)
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RT8206A/B
Functional Description
(Pin Reference Output. Bypass with 0.22uF capacitor. source 50uA external loads. Loading degrades output accuracy according load-regulation error. (Pin Frequency Select Input. (VOUT1/VOUT2 switching frequency, respectively) VCC, (200kHz 250kHz) REF, (300kHz 375kHz) GND, (400kHz 500kHz) (Pin Analog Supply Voltage Input Core. Bypass with ceramic capacitor ENLDO (Pin Enable Input. REF/LDO enabled ENLDO within logic high level disable ENLDO less than logic level. (Pin Internal Connection. (Pin Power-supply Input. used constant on-time shot circuits. also used power linear regulators. linear regulators powered SMPS1 VOUT1 greater than 4.66V tied VOUT1. Connect battery input bypass with capacitor. (Pin Linear-Regulator Output. provide total 70mA external loads. regulates fixed output. When within switchover threshold, internal regulator shuts down output connects through switch. Bypass output with minimum 4.7uF ceramic. (Pin switchover source voltage input LDO.
DS8206A/B-03 December 2009
VOUT1 (Pin SMPS1 Output Voltage-Sense Input. Connect this SMPS1 output. VOUT1 input Constant on-time-PWM one-shot circuit. also serves SMPS1 feedback input fixed-voltage mode. (Pin SMPS1 Feedback Input. Connect fixed operation. Connect resistive voltagedivider from VOUT1 adjust output from 5.5V. ILIM1 (Pin SMPS1 Current-Limit Adjustment. PHASE1 current-limit threshold 1/10th voltage seen ILIM1 over 0.5V range. There internal current source from ILIM1. logic current limit threshold default 100mV ILIM1 higher than (VCC 1V). PGOOD1 (Pin SMPS1 Power-Good Open-Drain Output. PGOOD1 when SMPS1 output voltage more than 7.5% below normal regulation point during soft-start. PGOOD1 high impedance when output regulation soft-start circuit terminated. PGOOD1 shutdown. (Pin SMPS1 Enable Input. SMPS1 will enabled greater than logic high level disabled less than logic level. connected REF, SMPS1 starts after SMPS2 reaches regulation (delay start). Drive below 0.8V clear fault level reset fault latches. UGATE1 (Pin High-Side MOSFET Floating Gate-Driver Output SMPS1. UGATE1 swings between PHASE1 BOOT1. PHASE1 (Pin Inductor Connection SMPS1. PHASE1 internal lower supply rail UGATE1 high-side gate driver. PHASE1 current-sense input SMPS1.
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RT8206A/B
BOOT1 (Pin Boost Flying Capacitor Connection SMPS1. Connect external capacitor according typical application circuits. LGATE1 (Pin SMPS1 Synchronous-Rectifier Gate-drive Output. LGATE1 swings between PGND PVCC. PVCC (Pin PVCC supply voltage low-side MOSFET driver LGATEx. Connect power source PVCC (bypass with MLCC capacitor PGND necessary). There internal connecting from PVCC VCC. Make sure that both PVCC bypassed with MLCC capacitors. SECFB (Pin (RT8206A) SECFB used monitor optional external charge pump. Connect resistive voltage-divider from charge pump output detect output. SECFB drops below threshold voltage, LGATE1 will turned 300ns. This will refresh external charge pump driven LGATE1 without over-discharging output voltage. (Pin (RT8206B) Internal Connection. [Pin Exposed (33)] Analog Ground both SMPS LDO. exposed must soldered large connected maximum power dissipation. PGND (Pin Power Ground SMPS controller. Connect PGND externally underside exposed pad. LGATE2 (Pin SMPS2 Synchronous-Rectifier Gate-drive Output. LGATE2 swings between PGND PVCC. BOOT2 (Pin Boost Flying Capacitor Connection SMPS2. Connect this external capacitor according typical application circuits.
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PHASE2 (Pin Inductor Connection SMPS2. PHASE2 internal lower supply rail UGATE2 high-side gate driver. PHASE2 current-sense input SMPS2. UGATE2 (Pin High-Side MOSFET Floating Gate-Driver Output SMPS2. UGATE2 swings between PHASE2 BOOT2. (Pin SMPS2 Enable Input. SMPS2 will enabled greater than logic high level disabled less than logic level. connected REF, SMPS2 starts after SMPS1 reaches regulation (delay start). Drive below 0.8V clear fault level reset fault latches. PGOOD2 (Pin SMPS2 Power-Good Open-Drain Output. PGOOD2 when SMPS2 output voltage more than 7.5% below normal regulation point during soft-start. PGOOD2 high impedance when output regulation soft-start circuit terminated. PGOOD2 shutdown. SKIP (Pin SMPS Operation Mode Control. SKIP operation SKIP Ultrasonic Mode operation SKIP operation. VOUT2 (Pin SMPS2 Output Voltage-Sense Input. Connect this SMPS2 output. VOUT2 input constant on-time-PWM one-shot circuit. also serves SMPS2 feedback input fixed-voltage mode. ILIM2 (Pin SMPS2 Current-Limit Adjustment. PHASE2 current-limit threshold 1/10th voltage seen ILIM2 over 0.5V range. There internal current source from ILIM2. logic current limit threshold default 100mV value ILIM2 higher than (VCC 1V).
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(Pin SMPS2 Feedback Input. Connect fixed 3.3V operation. Connect resistive voltagedivider from VOUT2 adjust output from 5.5V.
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Absolute Maximum Ratings
(Note VIN, ENLDO -0.3V BOOTx -0.3V PHASEx -0.3V <20ns BOOTx PHASEx -0.3V VCC, ENx, SKIP, TON, PVCC, PGOODx, -0.3V LDO, FBx, VOUTx, SECFB, REF, ILIMx -0.3V (VCC 0.3V) UGATEx PHASEx -0.3V (PVCC 0.3V) <20ns 7.5V LGATEx, -0.3V (PVCC 0.3V) <20ns -2.5V 7.5V PGND -0.3V 0.3V Power Dissipation, 25°C WQFN-32L 2.778W Package Thermal Resistance (Note WQFN-32L 5x5, 36°C/W WQFN-32L 5x5, 7°C/W Junction Temperature 150°C Lead Temperature (Soldering, sec.) 260°C Storage Temperature Range -65°C 150°C Susceptibility (Note (Human Body Mode) (Machine Mode) 200V
Recommended Operating Conditions
(Note
Input Voltage, Junction Temperature Range -40°C 125°C Ambient Temperature Range -40°C 85°C
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continued
RT8206A/B
Electrical Characteristics
(VIN 12V, VCC, VBYP PVCC VENLDO Load LDO, VOUT1, VOUT2 REF, 25°C, unless otherwise specified)
Parameter Input Supply
Symbol
Conditions
Unit
25V, Both SMPS Off, ENLDO 25V, Shutdown Supply VIN_SHDH Current ENLDO Both SMPSs Quiescent Power SKIP GND, VCC, Consumption VOUT1 5.3V, (Note VOUT2 3.5V SMPS Output Voltage 25V, FB1= GND, VOUT1 Output Voltage VOUT1 SKIP Fixed Mode Standby Supply Current VIN_SBY VOUT2 Output Voltage Fixed Mode Output Adjustable Mode SECFB Voltage Output Voltage Adjust Range Adjustable-mode Threshold Voltage Load Regulation Line Regulation Time On-Time Pulse Width UGATEx Minimum Off-Time Ultrasonic Mode Frequency Soft Start Soft-Start Time Current Sense Current Limit Threshold (Default) Current Limit Current Source
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4.975 3.285 1.975 1.92 -1895 1227
5.05 3.33 -0.4 -0.1 -1.7 -1.5 0.005 2105 1110 1403 1052
5.125 3.375 2.025 2.08 0.55 -2315 1221 1579 1209
VOUT2 SECFB
25V, SKIP (RT8206A) SMPS1, SMPS2 Fixed Adj-Mode comparator threshold Either SMPS, SKIP
VLOAD VLINE
Either SMPS, SKIP REF, Either SMPS, SKIP GND, Either SMPS, SMPS1 5.05V (200kHz) SMPS2 3.33V (250kHz) SMPS1 5.05V (300kHz) SMPS2 3.33V (375kHz) SMPS1 5.05V (400kHz) SMPS2 3.33V (500kHz)
LGATEx SKIP Zero full limit from Enable
ILIMx PHASEx LIMX
4.75
5.25
continued
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RT8206A/B
Parameter Adjustment Range Current-Limit Threshold Zero-Current Threshold Internal Regulator Reference Output Voltage Output Current Short-Circuit Current Switchover Threshold VBYP VLDO ILDO GND, 25V, 70mA GND, GND, Falling Edge, Rising Edge Regulation Point BYP, 10mA External Load IREF 50uA Regulation Rising Edge Falling Edge with Respect Internal Reference, Falling Edge, Hysteresis Falling Edge High State, Forced 5.5V ISINK VFB_OVP with Respect Internal Ref. with 50mV Overdrive with Respect Internal Ref. tSHDN_UVP From Enable -4.53 -1.98 -3.9 -200 4.66 -4.35 4.05 -300 4.79 2.02 -4.5 Symbol Conditions VILIMx LIMx RILIMx PHASEx VILIMx 0.5V VILIMx VILIMx -Typ -Unit
SKIP REF, PHASEx
Switchover Equivalent Resistance Output Voltage Load Regulation Sink Current UVLO PVCC UVLO Threshold Power Good PGOODx Threshold PGOODx Propagation Delay PGOODx Leakage Current PGOODx Output Voltage Fault Detection Trip Threshold Propagation Delay Trip Threshold Shutdown Blanking Time Thermal Shutdown Thermal Shutdown Thermal Shutdown Hysteresis Logic Input FB1/FB2 Input Voltage TSHDN PVCC VREF
-7.5
Level (Internal Fixed VOUTx) High Level (Internal Fixed VOUTx)
-VCC-1
continued
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RT8206A/B
Parameter SKIP Input Voltage Symbol Conditions Level (DEM) Level (Ultrasonic Mode) High Level (PWM Mode) VOUT1 VOUT2 (400kHz 500kHz) Setting Voltage VOUT1 VOUT2 (300kHz 375kHz) VOUT1 VOUT2 (200kHz 250kHz) Clear Fault Level SMPS Level Input Voltage Delay Start SMPS Level ENLDO Input Voltage VENLDO Rising Edge Falling Edge ENLDO Input Leakage Current TON, SKIP SECFB (RT8206A) Internal BOOT Switch Internal Boost Charging Switch On-Resistance Power MOSFET Drivers UGATEx Driver Sink/Source Current LGATEx Driver Source Current LGATEx Driver Sink Current UGATEx On-Resistance LGATEx On-Resistance Dead Time UGATEx Forced LGATEx Forced LGATEx Forced BOOTx PHASEx Forced LGATEx, High State LGATEx, State Rising Rising PVCC BOOTx -1.8 -1.8 -1.8 0.94 -1.6 -Max -0.8 -0.8 -2.0 1.06 Unit
Note Stresses beyond those listed under Absolute Maximum Ratings" cause permanent damage device. These stress ratings only, functional operation device these other conditions beyond those indicated operational sections specifications implied. Exposure absolute maximum rating conditions extended periods affect device reliability. Note Devices sensitive. Handling precaution recommended. Note device guaranteed function outside operating conditions. Note measured natural convection 25°C high effective four layers thermal conductivity test board JEDEC 51-7 thermal measurement standard. Note PVIN PPVCC
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Typical Operating Characteristics
VOUT1 Efficiency Load Current
VOUT1 Efficiency Load Current
Mode
Mode
Efficiency
Efficiency
0.001 0.01
Ultrasonic Mode Mode
Ultrasonic Mode
Mode 12V, VCC, GND, VCC, ENLDO VIN,
0.01
VCC, GND, VCC, ENLDO VIN,
0.001
Load Current
Load Current
VOUT1 Efficiency Load Current
VOUT2 Efficiency Load Current
Mode
Mode
Efficiency
0.001 0.01
Efficiency
0.001 0.01
Ultrasonic Mode Mode 25V, VCC, GND, VCC, ENLDO VIN,
Ultrasonic Mode Mode VCC, VCC, GND, ENLDO VIN,
Load Current
Load Current
VOUT2 Efficiency Load Current
VOUT2 Efficiency Load Current
Mode
Efficiency
Efficiency
0.001 0.01
0.001
Mode Ultrasonic Mode Mode 25V, VCC, VCC, GND, ENLDO VIN,
0.01
Ultrasonic Mode Mode 12V, VCC, VCC, GND, ENLDO VIN,
Load Current
Load Current
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VOUT1 Switching Frequency Load Current
VOUT1 Switching Frequency Load Current
Switching Frequency (kHz)
Switching Frequency (kHz)
VCC, GND, VCC, ENLDO VIN, Mode
12V, VCC, GND, VCC, ENLDO VIN, Mode
Ultrasonic Mode Mode
0.01
Ultrasonic Mode Mode
0.01
0.001
0.001
Load Current
Load Current
VOUT1 Switching Frequency Load Current
VOUT2 Switching Frequency Load Current
Switching FrequencyY (kHz)
Switching Frequency (kHz)
25V, VCC, GND, VCC, ENLDO VIN, Mode
VCC, VCC, GND, ENLDO VIN, Mode
Ultrasonic Mode Mode
0.01
Ultrasonic Mode Mode
0.01
0.001
0.001
Load Current
Load Current
VOUT2 Switching Frequency Load Current
VOUT2 Switching Frequency Load Current
Switching Frequency (kHz)
Switching Frequency (kHz)
12V, VCC, VCC, GND, ENLDO VIN, Mode
25V, VCC, VCC, GND, ENLDO VIN, Mode
Ultrasonic Mode Mode
0.01
Ultrasonic Mode Mode
0.01
0.001
0.001
Load Current
Load Current
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RT8206A/B
Output Voltage Output Current
5.04
VREF Output Current
2.00500 2.00475
12V, GND, ENLDO
12V, GND, ENLDO
5.036
Output Voltage
2.00450
5.032
2.00425 2.00400 2.00375 2.00350 2.00325
5.028
5.024
5.02
2.00300
Output Current (mA)
Output Current (uA)
Load Battery Current Input Voltage
Standby Current Input Voltage
VCC, VCC, ENLDO
Load, GND, ENLDO
Battery Current (mA)
Mode
Standby Current (uA)
Ultrasonic Mode
Standby Current
Mode
Input Voltage
Input Voltage
Shutdown Current Input Voltage
VREF Temperature
2.05 2.04 2.03 2.02
Load VOUT1, VOUT2, REF, GND, ENLDO
12.6V
Shutdown Current (uA)
Shutdown Current
2.01 2.00 1.99 1.98 1.97 1.96 1.95
Input Voltage
Temperature (°C)
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RT8206A/B
Power from
Mode
Power from
(10V/Div) (5V/Div) (2V/Div) (10V/Div)
Load, 12V, VCC, VCC, GND, ENLDO
(5V/Div) VOUT1 (5V/Div) (2A/Div) PGOOD1 (5V/Div)
Load, 12V, VCC, VCC, GND, ENLDO
Time (400s/Div)
Time (1ms/Div)
Power from
Mode Mode
Power from
(5V/Div) VOUT1 (5V/Div) (2A/Div) PGOOD1 (5V/Div)
(5V/Div) VOUT1 (5V/Div)
(2A/Div)
Load, 12V, VCC, VCC, GND, ENLDO
PGOOD1 (5V/Div)
ILOAD 12V, VCC, VCC, GND, ENLDO
Time (1ms/Div)
Time (1ms/Div)
Power from
Mode Mode
Power from
(5V/Div) VOUT2 (5V/Div) (2A/Div) PGOOD2 (5V/Div)
(5V/Div) VOUT2 (5V/Div) (2A/Div) PGOOD2 (5V/Div)
Load, 12V, VCC, GND, VCC, ENLDO
Load, 12V, VCC, GND, VCC, ENLDO
Time (1ms/Div)
Time (1ms/Div)
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RT8206A/B
Power from
Mode
Power from (Delay Start)
(5V/Div) VOUT2 (5V/Div) (2A/Div) PGOOD2 (5V/Div)
(5V/Div) (5V/Div)
ILOAD 12V, VCC, GND, VCC, ENLDO
VOUT1 (2V/Div) VOUT2 (2V/Div)
12V, VCC, ENLDO
Time (1ms/Div)
Time (400s/Div)
Power from (Delay Start)
Power from
(10V/Div) VOUT1 (5V/Div) UGATE1 (20V/Div) LGATE1 (5V/Div)
(5V/Div) (5V/Div) VOUT1 (2V/Div) VOUT2 (2V/Div)
12V, VCC, ENLDO
12V, VCC, SKIP VCC, ENLDO
Time (400s/Div)
Time (10ms/Div)
VOUT1 Load Transient Response
Mode,
VOUT2 Load Transient Response
Mode,
VOUT1_ac(50mV/Div)
coupled
VOUT2_ac(50mV/Div)
coupled
(5A/Div) LGATE1 (5V/Div)
(2A/Div) LGATE2 (5V/Div)
VCC, SKIP VCC, ENLDO VIN,
VCC, SKIP VCC, ENLDO VIN,
Time (20s/Div)
Time (20s/Div)
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RT8206A/B
VOUT1 (5V/Div) PGOOD1 (5V/Div) VOUT2 (5V/Div) PGOOD2 (5V/Div)
12V, VCC, SKIP GND, ENLDO
VOUT1 (5V/Div) (10A/Div) UGATE1 (20V/Div) LGATE1 (5V/Div)
12V, VCC, SKIP VCC, ENLDO
Time (500s/Div)
Time (10s/Div)
Power Short Circuit
VOUT1 (1V/Div) (5A/Div) UGATE1 (20V/Div) LGATE1 (5V/Div)
VOUT1 Short
12V, VCC, SKIP VCC, ENLDO
Time (400s/Div)
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RT8206A/B
Application Information
RT8206A/B dual, high efficiency, Mach ResponseDRVdual ramp valley mode synchronous buck controller. controller designed low-voltage power supplies notebook computers. Richtek Mach Response technology specifically designed providing 100ns "instant-on" response load steps while maintaining relatively constant operating frequency inductor operating point over wide range input voltages. DRVmode modulator specifically designed have better noise immunity such dual output application. RT8206A/B achieves high efficiency reduced cost eliminating current-sense resistor found traditional current-mode PWMs. Efficiency further enhanced ability drive very large synchronous rectifier MOSFETs. RT8206A/B includes (LDO) linear regulator which step down battery voltage supply both internal circuitry gate drivers. When VOUT1 voltage above 4.66V, automatic circuit turns linear regulator powers device from VOUT1 through connected VOUT1. Operation Mach ResponseDRVmode controller relies output filter capacitor's effective series resistance (ESR) current-sense resistor, output ripple voltage provides ramp signal. Refer function block diagram, UGATE driver will turned beginning each cycle. After internal oneshot timer expires, UGATE driver will turned off. pulse width this shot determined converter's input voltage output voltage keep frequency fairly constant over input voltage range. Another one-shot sets minimum off-time (300ns typ.). on-time one-shot triggered error comparator high, low-side switch current below currentlimit threshold, minimum off-time one-shot timed out. Frequency On-Time Control Mach Responsecontrol architecture runs with pseudo-constant frequency feed-forwarding input output voltage into on-time one-shot timer. high-side switch on-time inversely proportional input voltage measured VIN, proportional output voltage. on-time given On-Time= (VOUT VIN) There pin-strap connector (Table One-shot timing error increases shorter ontime setting fixed propagation delays that approximately ±15% high frequency ±10% frequency. on-time guaranteed Electrical Characteristics tables influenced switching delays external high-side power MOSFET. external factors that influence switching-frequency accuracy resistive drops conduction loops (including inductor board resistance) dead-time effect. These effects largest contributors change frequency with changing load current. dead-time effect increases effective on-time, reducing switching frequency both dead times. occurs only mode (SKIP high) when inductor current reverses light negative load currents. With reversed inductor current, inductor's causes PHASEX high earlier than normal, extending ontime period equal low-to-high dead time. loads above critical conduction point, actual switching frequency (VOUT +VDROP1) (VIN VDROP1 VDROP2 VDROP1 parasitic voltage drops inductor discharge path, including synchronous rectifier, inductor, board resistances; VDROP2 resistances charging path; ontime calculated RT8206A/B. Table Setting Frequency Table VOUT1 3.33s 2.5s K-Factor VOUT1 200kHz 300kHz 400kHz Frequency VOUT2 2.67s K-Factor VOUT2 250kHz 375kHz 500kHz Frequency Approximate ±10% ±12.5% ±15% K-Factor Error
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RT8206A/B
Operation Mode Selection RT8206A/B supports three operation modes: DiodeEmulation Mode, Ultrasonic Mode, Forced-CCM Mode. Users operation mode SKIP pin. three operation modes will introduced follows. Diode-Emulation Mode (SKIP GND) Diode-Emulation mode, RT8206A/B automatically reduces switching frequency light-load conditions maintain high efficiency. This reduction frequency achieved smoothly without increase VOUTx ripple load regulation. output current decreases from heavy-load condition, inductor current also reduced, eventually comes point that valley touches zero current, which boundary between continuous conduction discontinuous conduction modes. emulating behavior diodes, low-side MOSFET allows only partial negative current when inductor free-wheeling current reach negative. load current further decreases, takes longer longer discharge output capacitor level that requires next "ON" cycle. on-time kept same that heavy-load condition. reverse, when output current increases from light load heavy load, switching frequency increases preset value inductor current reaches continuous conduction. transition load point light-load operation calculated following equation.
ILOAD (VIN VOUT
switching waveforms appear noisy asynchronous when light loading causes Diode-Emulation operation, this normal operating condition that results high light-load efficiency. Trade-offs noise light-load efficiency made varying inductor value. Generally, inductor values produce broader efficiency load curve, while higher values result higher full-load efficiency (assuming that coil resistance remains fixed) less output voltage ripple. Penalties using higher inductor values include larger physical size degraded load-transient response (especially input-voltage levels). Ultrasonic Mode (SKIP REF) Connecting SKIP activates unique DiodeEmulation mode with minimum switching frequency above 25kHz. This ultrasonic mode eliminates audiofrequency modulation that would otherwise present when lightly loaded controller automatically skips pulses. ultrasonic mode, low-side switch gate-driver signal with internal oscillator (>25kHz). Once internal oscillator triggered, ultrasonic controller forces LGATEx high, turning low-side MOSFET induce negative inductor current. point that output voltage higher than that REF, controller turns low-side MOSFET (LGATEx pulled low) triggers constant on-time (UGATEx driven high). When on-time expired, controller re-enables lowside MOSFET until controller detects that inductor current dropped below zero-crossing threshold. Forced-CCM Mode (SKIP VCC) low-noise, forced-CCM mode (SKIP VCC) disables zero-crossing comparator, which controls low-side switch on-time. This causes low-side gate-driver waveform become complement high-side gatedriver waveform. This turn causes inductor current reverse light loads loop strives maintain duty ratio VOUT/VIN. benefit forcedCCM mode keep switching frequency fairly constant, comes cost no-load battery current 10mA 40mA, depending external MOSFETs.
where given On-time.
Slope OUT) peak
iLoad peak
Figure Boundary Condition CCM/DEM
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RT8206A/B
Reference Linear Regulator (REF, Charge Pump) reference (REF) accurate within over temperature, making useful precision system reference. Bypass with 0.22uF(MIN) capacitor. supply 50uA external loads. Loading degrades output accuracy according load-regulation error. internal regulator produces fixed output voltage regulator supply 70mA external loads. Bypass with minimum 4.7F ceramic capacitor. When output voltage VOUT1 higher than switchover threshold, internal N-Channel MOSFET switch connects VOUT1 through while simultaneously shutting down internal linear regulator. typical application circuit figure, external charge pump driven LGATE1. When LGATE1 low, charge sourced from VOUT1. voltage equal VOUT1 minus diode drop. When LGATE1 transitions high, charge from will transfer through charge VLGATE1 plus VC5. LGATE1 transients next cycle, will charge voltage minus diode drop through Finally, charges through when LGATE1 transi switched high. output voltage VOUT1 VLGATE1 Where VLGATE1 peak voltage LGATE1 driver forward diode dropped across Schottkys SECFB (RT8206A) used monitor charge pump through resistive divider. event when SECFB drops below detection circuit forces LGATE1 300ns allow recharge SECFB rise above event overload where SECFB reach more than monitor will deactivated. SECFB 17mV hysteresis ripple should enough bring SECFB voltage above threshold hysteresis, 17mV) 51mV. Reducing decoupling capacitor placing small ceramic capacitor (10pF 47pF) parallel will upper SECFB resistor feedback network (R11
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Figure will also increase robustness charge pump. Current-Limit Setting (ILIMx) RT8206A/B cycle-by-cycle current limiting control. current-limit circuit employs unique "valley" current sensing algorithm. magnitude currentsense signal PHASEx above current-limit threshold, allowed initiate cycle (Figure actual peak current greater than current-limit threshold amount equal inductor ripple current. Therefore, exact current-limit characteristic maximum load capability function sense resistance, inductor value, battery voltage, output voltage.
peak ILoad ILIM
Figure Valley Current-Limit RT8206A/B uses on-resistance synchronous rectifier current-sense element. worsecase maximum value RDS(ON) from MOSFET datasheet, margin 0.5%/°C rise RDS(ON) with temperature. current-limit threshold adjusted with external resistor RT8206A/B ILIMx. current-limit threshold adjustment range from 50mV 200mV. adjustment mode, current-limit threshold voltage precise 1/10 voltage seen ILIMx. threshold defaults 100mV when ILIMx connected VCC. logic threshold switchover 100mV default value higher than VCC-1V. Carefully observe board layout guidelines ensure that noise errors corrupt current-sense signal PHASEx GND. Mount place close low-side MOSFET.
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RT8206A/B
MOSFET Gate Driver (UGATEx, LGATEx) high-side driver designed drive high-current, RDS(ON) N-MOSFET(s). When configured floating driver instantaneous drive current supplied flying capacitor between BOOTx PHASEx pins. dead time prevent shoot through internally generated between high-side MOSFET low-side MOSFET lowside MOSFET high-side MOSFET low-side driver designed drive high current RDS(ON) N-MOSFET(s). internal pulldown transistor that drives LGATEx robust, with typical onresistance. bias voltage typically delivered from PVCC through supply. instantaneous drive current supplied input capacitor connected between PVCC GND. high-current applications, some combinations highand low-side MOSFETs might encountered that will cause excessive gate-drain coupling, which lead efficiency-killing, EMI-producing shoot-through currents. This often remedied adding resistor series with BOOTx, which increases turn-on time high-side MOSFET without degrading turn-off time (Figure
switching keeping UGATEx LGATEx when PVCC below outputs begin ramp once PVCC exceeds UVLO threshold enable. Power-Good Output (PGOODx) PGOODx open-drain type output. PGOODx actively held soft-start, standby, shutdown. released when VOUTx voltage above than 92.5% nominal regulation point. PGOODx goes 7.5% below nominal regulator point. Output Over voltage Protection (OVP) output voltage continuously monitored over voltage protection. When output voltage VOUTx above voltage, over voltage protection will enabled, output exceeds over voltage threshold, over voltage fault protection will triggered LGATEx low-side gate drivers forced high. This activates low-side MOSFET switch, which rapidly discharges output capacitor reduces output voltage. Once over-voltage fault condition set, only reset toggling ENLDO, ENx, cycling (POR.) Output Under-Voltage Protection (UVP) output voltage continuously monitored under voltage protection. output less than error-amplifier trip voltage, under voltage protection will triggered, then both UGATEx LGATEx gate drivers will forced low. will ignored least (typ.) after start-up after rising edge ENx. Toggle cycle (POR) clear under-voltage fault latch restart controller. only applies BUCK outputs. Thermal Protection RT8206A/B thermal shutdown protection function prevent from overheating. Thermal shutdown occurs when temperature exceeds +150°C. internal circuitry will shut down during thermal shutdown. RT8206A/B trigger thermal shutdown were supplied from VOUTx, while input voltage drawing current that high from LDO. Even supplied from VOUTx, overloading
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BOOTx
UGATEx PHASEx
Figure Reducing UGATEx Rise Time Soft-Start built-in soft-start used prevent surge current from power supply input after enabled. typical softstart duration period. maximum allowed current limit segmented steps 20%, 40%, 60%, 100% during this period. current limit steps eliminate VOUT folded-back soft-start duration. UVLO Power-on reset (POR) occurs when rises above approximately 3.7V (typ.), resetting fault latches. PVCC undervoltage-lockout (UVLO) circuitry inhibits
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RT8206A/B
causes large power dissipation automatic switches, which result thermal shutdown. Discharge Mode When standby shutdown mode occurs, output under voltage fault latch set, outputs discharge mode triggered. During discharge mode, output capacitor will discharged through internal switch. Shutdown Mode RT8206A/B SMPS1, SMPS2 have independent enabling control. Drive ENLDO, below precise input falling-edge trip level place RT8206A/B low-power shutdown state. RT8206A/B consumes only 20uA quiescent current while shutdown. When shutdown mode activated, reference turns off. accurate falling-edge threshold ENLDO used detect specific analog voltage level shutdown device. Once shutdown, 1.6V rising-edge threshold activates, providing sufficient hysteresis most application. Power-Up Sequencing On/Off Controls (ENx) control SMPS power-up sequencing. When RT8206A/B applies single channel mode, enables respective outputs when voltage rising above 2.5V, disables respective outputs when voltage falling below 1.8V. Connecting other force latter output starts after former regulates. both forced connect REF, both outputs will always wait regulation other one. However, this situation, neither will regulation. Output Voltage Setting (FBx) Connect directly fixed output (VOUT1). Connect directly fixed 3.3V output (VOUT2). output voltage also adjusted from 5.5V with resistor-divider network (Figure following equation adjusting output voltage. Choose approximately 10k, solve using following equation
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UGATEx PHASEx LGATEx VOUTx
VOUTx VFBx
Where VFBx (typ.).
OUTx
Figure Setting VOUTx with Resistor-Divider Output Inductor Selection switching frequency (on-time) operating point ripple LIR) determine inductor value follows
(VIN VOUT ILOAD(MAX)
Where ratio peak-to-peak ripple current average inductor current. Find low-loss inductor having lowest possible resistance that fits allotted dimensions. Ferrite cores often best choice, although powdered iron inexpensive work well 200kHz. core must large enough prevent from saturating peak inductor current (IPEAK) IPEAK ILOAD(MAX) [(LIR ILOAD(MAX)] This inductor ripple current also impacts transient-response performance, especially VOUTx differences. inductor values allow inductor current slew faster, replenishing charge removed from output filter capacitors sudden load step. peak amplitude output transient. VSAG also features function output transient (VSAG) also function maximum duty factor, which calculated from on-time minimum off-time (ILOAD OUTx TOFF(MIN) VSAG VOUTx COUT VOUTx TOFF(MIN) Where minimun off-time (TOFF(MIN)) 300ns (typ.) from Table
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Output Capacitor Selection output filter capacitor must have enough meet output ripple load-transient requirements, it's commanded keep feedback voltage between 12mV. Also, capacitance value must high enough absorb inductor energy going from full-load noload condition without tripping circuit. core voltage converters other applications where output subject violent load transients, output capacitor's size depends much needed prevent output from dipping under load transient. Ignoring finite capacitance
VP-P ILOAD(MAX)
Double-pulsing occurs noise output because that there enough voltage ramp output voltage signal. This "fools" error comparator into triggering cycle immediately after 300ns minimum off-time period expired. Double-pulsing more annoying than harmful, resulting nothing worse than increased output ripple. However, indicate possible presence loop instability, which caused insufficient ESR. Loop instability result oscillations output after line load perturbations that trip over-voltage protection latch cause output voltage fall below tolerance limit. easiest method checking stability apply very fast zero-to-max load transient carefully observe output-voltage-ripple envelope overshoot ringing. helps simultaneously monitor inductor current with current probe. allow more than cycle ringing after initial step-response under- overshoot. Thermal Considerations continuous operation, exceed absolute maximum operation junction temperature. maximum power dissipation depends thermal resistance package, layout, rate surroundings airflow temperature difference between junction ambient. maximum power dissipation calculated following formula PD(MAX) TJ(MAX) Where J(MAX) maximum operation junction temperature, ambient temperature junction ambient thermal resistance. recommended operating conditions specification RT8206, maximum junction temperature 125°C. junction ambient thermal resistance layout dependent. WQFN-32L packages, thermal resistance 36°C/W standard JEDEC 51-7 four layers thermal test board. maximum power dissipation 25°C calculated following formula PD(MAX) (125°C 25°C) (36°C/W) 2.778W WQFN-32L packages
non-CPU applications, output capacitor's size depends much needed maintain acceptable level output voltage ripple
VP-P ILOAD(MAX)
There VP-P peak-to-peak output voltage ripple. Organic semiconductor capacitor(s) specialty polymer capacitor(s) recommended. Output Capacitor Stability Stability determined value zero relative switching frequency. point instability given following equation fESR COUT
high-value ceramic capacitors directly across outputs without taking precautions ensure stability. Large ceramic capacitors have high- zero frequency cause erratic, unstable operation. However, easy enough series resistance placing capacitors couple inches downstream from inductor connecting VOUTx divider close inductor. There related distinct ways including doublepulsing feedback loop instability unstable operation.
DS8206A/B-03
December 2009
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RT8206A/B
maximum power dissipation depends operating ambient temperature fixed J(MAX) thermal resistance RT8206A/B packages, Figure derating curves allows designer effect rising ambient temperature maximum power allowed.
sensitive analog traces components such VOUTx, FBx, GND, ENx, PGOODx, ILIMx, VCC, should placed away from high-voltage switching nodes such PHASEx, LGATEx, UGATEx BOOTx nodes avoid coupling. internal layer(s) ground plane(s) shield feedback trace from power traces components. Gather ground terminal capacitor(s), VOUTx capacitor(s), source low-side MOSFETs close possible. trace defined PHASEx node, which connects source high-side MOSFET, drain lowside MOSFET high-voltage side inductor, should short wide possible.
Maximum Power Dissipation
Four Layers
WQFN -32L
Ambient Temperature (°C)
Figure Derating Curves RT8206A/B Packages Layout Considerations Layout very important high frequency switching converter design. layout designed improperly, could radiate excessive noise contribute converter instability. following points must followed proper layout RT8206A/B. Connect low-pass filter from PVCC VCC, low-pass filter composed external capacitor internal resistor. Bypass with capacitor recommended. Place capacitor close within 12mm (0.5 inch) possible. Keep current limit setting network close possible Routing network should avoid coupling high-voltage switching node. Connections from drivers respective gate high-side low-side MOSFET should short possible reduce stray inductance. 0.65mm mils) wider trace.
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DS8206A/B-03
December 2009
RT8206A/B
Table Operation Mode Truth Table
Mode Power-UP Condition PVCC UVLO threshold Comment Transitions discharge mode after after becomes valid. remain active. ENLDO high, enabled Normal Operation. Over voltage Either output 111% nominal LGATEx forced high. active. Exited Protection level. toggling ENLDO. Both UGATEx LGATEx forced until enter Either output<70% nominal level Under voltage discharge mode terminates. active. after time-out expires output Protection Exited toggling ENLDO, EN1, enabled. EN2. Either SMPS output still high During discharge mode, output capacitor Discharge either standby mode shutdown discharges through internal switch. mode. startup threshold, Standby LGATEx stays low. active. ENLDO high. Shutdown EN1, EN2, ENLDO=low circuitry off. Thermal Shutdown +150°C circuitry off. Exit toggling ENLDO.
Table Power-Up Sequencing
ENLDO ">2V" High ">2V" High ">2V" High ">2V" High ">2V" High ">2V" High ">2V" High ">2V" High ">2V" High High High High
VEN2
High High High (after (after (after (after (after (after (after
powers powers powers powers powers powers powers
SMPS1 (after SMPS2
SMPS2 (after SMPS1
(after powers (after powers
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RT8206A/B
Outline Dimension
DETAIL
DETAIL Mark Options Note configuration identifier optional, must located within zone indicated.
Dimensions Millimeters 0.350 0.700 0.000 0.175 0.180 4.950 3.400 4.950 3.400 0.500 0.450 0.014 0.800 0.050 0.250 0.300 5.050 3.750 5.050 3.750 Dimensions Inches 0.028 0.000 0.007 0.007 0.195 0.134 0.195 0.134 0.020 0.018 0.031 0.002 0.010 0.012 0.199 0.148 0.199 0.148
Symbol
W-Type Package
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DS8206A/B-03
December 2009

RT8206A B

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