Richtek RT8248AGQW Schematic [ru]
®
RT8248A
Complete DDR Memory Power Supply Controller
General Description
The RT8248Aprovides a complete power supply forDDR2/ DDR3/DDR3L/LPDDR3/DDR4 memory systems. It integrates a synchronous PWM Buck controller with a 1.5A sink/source tracking linear regulator and buffered low noise reference.
The PWM controller provides the low quiescent current, high efficiency, excellent transient response, and high DC output accuracy needed for stepping down high-voltage batteries to generate low-voltage chipset RAM supplies in notebook computers. The constant on-time PWM control scheme handles wide input/output voltage ratios with ease and provides 100ns “instant-on” response to load transients while maintaining a relatively constant switching frequency.
The RT8248A achieves high efficiency at a reduced cost by eliminating the current-sense resistor found in traditional current mode PWMs. Efficiency is further enhanced by its ability to drive very large synchronous rectifier MOSFETs. The Buck conversion allows this device to directly step down high-voltage batteries for the highest possible efficiency.
The 1.5A sink/source LDO maintains fast transient response only requiring a 10μF ceramic output capacitor. In addition, the LDO supply input is available externally to significantly reduce the total power losses. The IC supports all of the sleep state controls placing VTT at high-Z in S3 and discharging VDDQ, VTT and VTTREF (soft-off) in S4/S5.
The RT8248A provides protections including OVP, UVP, and thermal shutdown and available in the WQFN-20L 3x3 package.
Features
PWM Controller
Adjustable Current Limit with Low-Side RDS(ON) Sensing
Low Quiescent Supply Current
Quick Load-Step Response within 100ns
1% VVDDQ Accuracy Over Line and Load
Adjustable 0.675V to 3.3V Output Range for 1.8V
(DDR2), 1.5V (DDR3), 1.35V (DDR3L), 1.2V (LPDDR3) and 1.2V (DDR4)
4.5V to 26V Battery Input Range
Resistor Adjustable Frequency
Over-/Under-Voltage Protection
Internal Voltage Ramp Soft-Start
Drives Large Synchronous Rectifier MOSFETs
Power Good Indicator
1.5A LDO (VTT), Buffered Reference (VTTREF)
Capable to Sink and Source Up to 1.5A
LDO Input Available to Optimize Power Losses
Requires Only 10μF Ceramic Output Capacitor
Integrated Divider Tracks 1/2 VDDQ for both VTT and VTTREF
Accuracy ±20mV for both VTTREF and VTT
Supports High-Z in S3 and Soft-Off in S4/S5
Simplified Application Circuit
VIN
VVDD |
VDD |
RT8248A |
TON |
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UGATE |
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PGOOD |
PGOOD |
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BOOT |
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VTT |
VTT |
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PHASE |
V |
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LGATE |
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VTTSNS |
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CS |
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FB |
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S3 |
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VTTREF |
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VDDQ |
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S5 |
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VID |
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GND VLDOIN |
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VDDQ
Copyright ©2014 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS8248A-04 October 2014 |
www.richtek.com |
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1 |
RT8248A |
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Applications |
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Ordering Information |
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DDR2/DDR3/DDR3L/LPDDR3/DDR4 Memory Power |
RT8248A |
Package Type |
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Supplies |
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Notebook computers |
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QW : WQFN-20L 3x3 (W-Type) |
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Lead Plating System |
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SSTL18, SSTL15 and HSTL bus termination |
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G : Green (Halogen Free and Pb Free) |
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Pin Configurations |
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Note : |
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(TOP VIEW) |
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Richtek products are : |
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VTT |
VLDOIN |
BOOT |
UGATE |
PHASE |
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RoHS compliant and compatible with the current require- |
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ments of IPC/JEDEC J-STD-020. |
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20 19 18 17 16 |
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Suitable for use in SnPb or Pb-free soldering processes. |
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VTTGND |
1 |
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15 |
LGATE |
Marking Information |
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VTTSNS |
2 |
GND |
14 |
PGND |
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GND |
3 |
13 |
CS |
RT8248AGQW |
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VTTREF |
4 |
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21 |
12 |
VDD |
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VDDQ |
5 |
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11 |
VID |
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5E= : Product Code |
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6 |
7 |
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5E=YM |
YMDNN : Date Code |
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FB S3 S5 |
TON |
PGOOD |
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DNN |
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WQFN-20L 3x3 |
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Functional Pin Description
Pin No. |
Pin Name |
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Pin Function |
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1 |
VTTGND |
Power Ground for the VTT LDO. |
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2 |
VTTSNS |
Voltage Sense Input for the VTT LDO. Connect to the terminal of the VTT_LDO |
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output capacitor. |
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3, 21 |
GND |
The exposed pad must be soldered to a large PCB and connected to GND for |
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(Exposed Pad) |
maximum power dissipation. |
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4 |
VTTREF |
VTTREF Buffered Reference Output. |
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5 |
VDDQ |
Reference Input for VTT and VTTREF. |
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6 |
FB |
Feedback Voltage Input. Connect to a resistive voltage divider from VDDQ to |
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GND to adjust the output voltage. |
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7 |
S3 |
VTT LDO Enable Control Input. Do not leave this pin floating. |
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8 |
S5 |
PWM Enable Control Input. Do not leave this pin floating. |
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9 |
TON |
Set the UGATE On-Time Through a Pull-Up Resistor Connecting to VIN. |
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10 |
PGOOD |
Power Good Open-Drain Output. In high state when VDDQ output voltage is |
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within the target range. |
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11 |
VID |
Internal Reference Voltage Setting. |
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12 |
VDD |
Supply Voltage Input for the Analog Supply and LGATE Gate Driver. |
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13 |
CS |
Current Limit Threshold |
Setting Input. Connect to GND through the voltage |
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setting resistor. |
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14 |
PGND |
Power Ground for Low-Side MOSFET. |
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15 |
LGATE |
Low-Side Gate Driver Output for VDDQ. |
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16 |
PHASE |
Switch Node. External inductor connection for VDDQ and behave as the current |
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sense comparator input for Low-Side MOSFET RDS(ON) sensing. |
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17 |
UGATE |
High-Side Gate Driver Output for VDDQ. |
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18 |
BOOT |
Bootstrap Supply for High-Side Gate Driver. |
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19 |
VLDOIN |
Power Supply for VTT LDO. |
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20 |
VTT |
Power Output for the VTT LDO. |
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Copyright ©2014 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
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www.richtek.com |
DS8248A-04 October 2014 |
2 |
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RT8248A
Function Block Diagram
Buck Controller
TRIG
VDDQ |
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On-Time |
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BOOT |
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TON |
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1-SHOT |
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R |
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+ Comp |
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VREF |
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+ |
S |
Q |
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UGATE |
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- |
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PHASE |
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+ |
OV |
Latch |
Min. TOFF |
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VDD |
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S1 |
Q |
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115%VREF |
- |
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TRIG |
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FB |
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+ |
UV |
Latch |
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LGATE |
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0.45V |
S1 |
Q |
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- |
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PGND |
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- |
DEM |
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85% VREF |
+ |
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SS Int |
SS Timer |
Thermal |
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+ |
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5µA |
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Shutdown |
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1/10 |
CS |
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S5 |
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Reference |
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Voltage |
VREF |
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Selector |
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VDD |
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VID |
PGOOD |
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VTT LDO |
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VDDQ |
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S5 |
Non-Tracking |
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Thermal |
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VTTREF |
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S3 |
Discharge |
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Shutdown |
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VLDOIN |
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+ |
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- |
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+ |
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- |
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GND |
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+ |
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VTT |
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- |
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+ |
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VTTSNS |
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- |
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VTTGND |
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Copyright ©2014 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS8248A-04 October 2014 |
www.richtek.com |
|
3 |
RT8248A
Operation
The RT8248A is a constant on-time synchronous stepdown controller. In normal operation, the high-side N-MOSFET is turned on when the output voltage is lower than VREF, and is turned off after the internal one-shot timer expires. While the high-side N-MOSFET is turned off, the low-side N-MOSFET is turned on to conduct the inductor current until next cycle begins.
Soft-Start (SS)
For internal soft-start function, an internal current source charges an internal capacitor to build the soft-start ramp voltage. The output voltage will track the internal ramp voltage during soft-start interval.
PGOOD
The power good output is an open-drain architecture. When the soft-start is finished, the PGOOD open-drain output will be high impedance.
Current Limit
The current limit circuit employs a unique “valley” current sensing algorithm. If the magnitude of the current sense signal at PHASE is above the current limit threshold, the PWM is not allowed to initiate a new cycle. The current limit threshold can be set with an external voltage setting resistor on the CS pin.
Over-Voltage Protection (OVP) & Under-Voltage Protection (UVP)
The output voltage is continuously monitored for overvoltage and under-voltage protection. When the output voltage exceeds its set voltage threshold( 115% of VOUT), UGATE goes low and LGATE is forced high. When the feedback voltage is less than 0.45V, under-voltage protection is triggered and then both UGATE and LGATE gate drivers are forced low. The controller is latched until VDD is re-supplied and exceeds the POR rising threshold voltage or S5 is reset.
VTT Linear Regulator and VTTREF
This VTT linear regulator employs ultimate fast response feedback loop so that small ceramic capacitors are enough for keeping track of VTTREF within 40mV at all conditions, including fast load transient. The VTTREF block consists of on-chip 1/2 divider, LPF and buffer. This regulator also has sink and source capability up to 10mA. Bypass VTTREF to GND with a 33nF ceramic capacitor for stable operation.
Copyright ©2014 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
www.richtek.com |
DS8248A-04 October 2014 |
4 |
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RT8248A |
Absolute Maximum Ratings (Note 1) |
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Supply Input Voltage, TON to GND ------------------------------------------------------------------------------------ |
−0.3V to 32V |
BOOT to PHASE ---------------------------------------------------------------------------------------------------------- |
−0.3V to 6V |
PHASE to GND |
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DC ----------------------------------------------------------------------------------------------------------------------------- |
−0.3V to 32V |
< 20ns ----------------------------------------------------------------------------------------------------------------------- |
−8V to 38V |
LGATE to GND |
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DC ----------------------------------------------------------------------------------------------------------------------------- |
−0.3V to 6V |
< 20ns ----------------------------------------------------------------------------------------------------------------------- |
−2.5V to 7.5V |
UGATE to PHASE |
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DC ----------------------------------------------------------------------------------------------------------------------------- |
−0.3V to 6V |
< 20ns ----------------------------------------------------------------------------------------------------------------------- |
−5V to 7.5V |
VDD, CS, S3, S5, VTTSNS, VDDQ, VID, VTTREF, VTT, VLDOIN, FB, PGOOD to GND ---------------- |
−0.3V to 6V |
PGND, VTTGND to GND ------------------------------------------------------------------------------------------------- |
−0.3V to 0.3V |
Other Pins------------------------------------------------------------------------------------------------------------------- |
−0.3V to 6.5V |
Power Dissipation, PD @ TA = 25°C |
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WQFN-20L 3x3 ------------------------------------------------------------------------------------------------------------ |
3.33W |
Package Thermal Resistance (Note 2) |
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WQFN-20L 3x3, θJA ------------------------------------------------------------------------------------------------------- |
30°C/W |
WQFN-20L 3x3, θJC ------------------------------------------------------------------------------------------------------ |
7.5°C/W |
Junction Temperature ----------------------------------------------------------------------------------------------------- |
150°C |
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------- |
260°C |
Storage Temperature Range -------------------------------------------------------------------------------------------- |
−65°C to 150°C |
ESD Susceptibility (Note 3) |
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HBM (Human Body Model) ---------------------------------------------------------------------------------------------- |
2kV |
Recommended Operating Conditions (Note 4) |
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Input Voltage, VIN --------------------------------------------------------------------------------------------------------- |
4.5V to 26V |
Control Voltage, VDD ----------------------------------------------------------------------------------------------------- |
4.5V to 5.5V |
Junction Temperature Range -------------------------------------------------------------------------------------------- |
−40°C to 125°C |
Ambient Temperature Range -------------------------------------------------------------------------------------------- |
−40°C to 85°C |
Electrical Characteristics
(VDD = 5V, VIN = 12V, RTON = 620kΩ, TA = 25°C, unless otherwise specified)
Parameter |
Symbol |
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Test Conditions |
Min |
Typ |
Max |
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Unit |
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PWM Controller |
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Quiescent Supply Current |
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FB Forced above the Regulation Point, |
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135 |
-- |
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A |
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VS5 |
= 5V, VS3 |
= 0V, Not Switching |
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TON Operating Current |
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RTON = 620k , VIN = 12V |
-- |
19 |
-- |
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A |
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IVLDOIN BIAS Current |
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VS5 |
= VS3 = 5V, VTT = No Load |
-- |
1 |
-- |
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A |
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IVLDOIN Standby Current |
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VS5 |
= 5V, VS3 |
= 0, VTT = No Load |
-- |
0.1 |
10 |
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A |
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Copyright ©2014 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
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DS8248A-04 October 2014 |
www.richtek.com |
|
5 |
RT8248A
Parameter |
Symbol |
Test Conditions |
Min |
Typ |
Max |
Unit |
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VDD |
-- |
0.1 |
10 |
A |
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Shutdown Current |
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TON |
-- |
0.1 |
5 |
A |
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ISHDN |
S5/S3 |
1 |
0.1 |
1 |
A |
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(VS5 = VS3 = 0V) |
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VLDOIN |
-- |
0.1 |
1 |
A |
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VID |
-- |
0.5 |
1 |
A |
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FB Error Comparator |
VREF |
VREF = 0.675V/0.75V |
1 |
0 |
1 |
% |
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Threshold |
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VDDQ Voltage Range |
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0.675 |
-- |
3.3 |
V |
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Switch Frequency |
fSW |
RTON = 620k, VIN = 12V, |
320 |
400 |
480 |
kHz |
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VDDQ = 1.5V, IOUT = 20A (Note 5) |
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Minimum Off-Time |
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250 |
400 |
550 |
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VDDQ Shutdown Discharge |
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VS5 = 0V, VS3 = 0V |
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15 |
-- |
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Resistance |
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Current Sensing |
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CS Pin Source Current |
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4.5 |
5 |
5.5 |
A |
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Zero Crossing Threshold |
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GND PHASE |
5 |
-- |
10 |
mV |
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Fault Protection |
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Current Limit (Positive) |
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GND PHASE, RCS = 160k |
70 |
80 |
90 |
mV |
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Output UV Threshold |
VUVP |
VFB Falling. For both VID is high or |
0.4 |
0.45 |
0.5 |
V |
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low. |
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UVP Latch Delay |
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FB Forced below UV Threshold |
-- |
30 |
-- |
s |
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OVP Threshold |
VOVP |
With Respect to Error Comparator |
110 |
115 |
120 |
% |
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Threshold |
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OVP Latch Delay |
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FB Forced above OV Threshold |
-- |
5 |
-- |
s |
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VDD POR Threshold |
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Rising Edge, Hysteresis = 120mV, |
3.9 |
4.2 |
4.5 |
V |
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PWM Disabled below this Level |
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Voltage Ramp Soft-Start Time |
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From S5 Going High to VFB = 0.675V |
-- |
1 |
-- |
mS |
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UV Blank Time |
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From S5 Signal Going High |
-- |
5 |
-- |
mS |
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Thermal Shutdown |
TSD |
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-- |
165 |
-- |
C |
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Driver On-Resistance |
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UGATE Gate Driver Source |
RUGATEsr |
BOOT PHASE Forced to 5V |
-- |
2.5 |
5 |
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UGATE Gate Driver Sink |
RUGATEsk |
BOOT PHASE Forced to 5V |
-- |
1.5 |
3 |
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LGATE Gate Driver Source |
RLGATEsr |
DL, High State |
-- |
2.5 |
5 |
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LGATE Gate Driver Sink |
RLGATEsk |
DL, Low State |
-- |
0.8 |
1.6 |
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Dead Time |
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LGATE Rising (Phase = 1.5V) |
-- |
40 |
-- |
ns |
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UGATE Rising |
-- |
40 |
-- |
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Internal Boost Charging Switch |
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VDD to BOOT, 10mA |
-- |
-- |
80 |
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On-Resistance |
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Copyright ©2014 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
www.richtek.com |
DS8248A-04 October 2014 |
6 |
|
RT8248A
Parameter |
Symbol |
Test Conditions |
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Min |
Typ |
Max |
Unit |
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Logic I/O |
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S3, S5 Input |
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Logic-High |
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2 |
-- |
-- |
V |
Voltage |
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Logic-Low |
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-- |
-- |
0.8 |
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Logic Input Current |
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S3, S5 = VDD / GND |
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1 |
0 |
1 |
A |
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VID Input |
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Logic-High |
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750 |
-- |
-- |
mV |
Threshold Voltage |
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Logic-Low |
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-- |
-- |
300 |
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PGOOD (Upper Side Threshold Decide by OV Threshold) |
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Trip Threshold (Falling) |
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Measured at FB, with Respect to |
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20 |
15 |
10 |
% |
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Reference, No Load. Hysteresis = 2% |
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Fault Propagation Delay |
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Falling Edge, FB Forced below |
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-- |
5 |
-- |
s |
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PGOOD Trip Threshold |
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Output Low Voltage |
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ISINK = 1mA |
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-- |
-- |
0.4 |
V |
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Leakage Current |
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ILEAK |
High State, Forced to 5V |
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-- |
-- |
1 |
A |
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VTT LDO |
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VDDQ = VLDOIN = 1.2V/1.35V/1.5V/ |
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20 |
-- |
20 |
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1.8V, |IVTT| = 0A |
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VDDQ = VLDOIN = 1.2V/1.35V/1.5V/ |
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30 |
-- |
30 |
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1.8V, |IVTT| < 1A |
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VTT Output Tolerance |
VVTTTOL |
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mV |
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VDDQ = VLDOIN = 1.2V/1.35V, |
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40 |
-- |
40 |
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|IVTT| < 1.2A |
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VDDQ = VLDOIN = 1.5V/1.8V, |
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40 |
-- |
40 |
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|IVTT| < 1.5A |
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VTT Source Current Limit |
IVTTOCLSRC |
VTT = 0V |
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1.6 |
2.6 |
3.6 |
A |
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VTT Sink Current Limit |
IVTTOCLSNK |
VTT = VDDQ |
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1.6 |
2.6 |
3.6 |
A |
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VVDDQ |
10 |
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A |
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VTT Leakage Current |
IVTTLK |
S5 = 5V, S3 = 0V, VTT = |
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-- |
10 |
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2 |
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VTTSNS Leakage Current |
IVTTSNSLK |
ISINK = 1mA |
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1 |
-- |
1 |
A |
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VTT Discharge Current |
IDSCHRG |
VDDQ = 0V, VTT = 0.5V, S5 = S3 = 0V |
10 |
30 |
-- |
mA |
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VVDDQ |
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VVTT = VVTTREF = |
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, |
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-- |
0.75 |
-- |
V |
VTTREF Output Voltage |
VVTTREF |
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2 |
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VVDDQ = 1.5V |
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VLDOIN = VVDDQ = 1.5V, |
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15 |
-- |
15 |
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VDDQ/2, VTTREF Output |
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|IVTTREF| < 10mA |
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VVTTREFTOL |
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mV |
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Voltage Tolerance |
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VLDOIN = VVDDQ = 1.8V, |
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18 |
-- |
18 |
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|IVTTREF| < 10mA |
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VTTREF Source Current Limit |
IVTTREFOCL |
VVTTREF = 0V |
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10 |
40 |
80 |
mA |
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Copyright ©2014 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS8248A-04 October 2014 |
www.richtek.com |
|
7 |
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