Richtek RT8237EZQW Schematic [ru]
®
RT8237E
High Efficiency Single Synchronous Buck PWM Controller
General Description
The RT8237E PWM controller provides high efficiency, excellent transient response, and high DC output accuracy needed for stepping down high voltage batteries to generate low voltage CPU core, I/O, and 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 RT8237E 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 and enter diode emulation mode at light load condition. The Buck conversion allows this device to directly step down high voltage batteries at the highest possible efficiency. The pre-set frequency selections minimize design effort required for new designs. The RT8237E is intended for CPU core, chipset, DRAM, or other low voltage supplies as low as 0.7V. The RT8237E is available in the WDFN-10L 3x3 package.
Features
zWide Input Voltage Range : 4.5V to 26V
zOutput Voltage Range : 0.7V to 3.3V
zBuilt-in 0.5% 0.7V Reference Voltage
zQuick Load-Step Response within 100ns
z4700ppm/°C Current Source for Current Limit
RDS(ON)
zAdjustable Current Limit with Low Side MOSFET
z4 Selectable Frequency Setting
zSoft-Start Control
zDrives Large Synchronous-Rectifier FETs
zIntegrated Boot Switch
zBuilt-in OVP/OCP/UVP
zThermal Shutdown
zPower Good Indicator
zRoHS Compliant and Halogen Free
Applications
zNotebook Computers
zCPU Core Supply
zChipset/RAM Supply as Low as 0.7V
zGeneric DC/DC Power Regulator
Simplified Application Circuit
RT8237E
VCC |
VCC |
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BOOT |
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PGOOD |
UGATE |
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EN |
PHASE |
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RF |
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CS |
LGATE |
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VIN
VOUT
GND
FB
Copyright ©2012 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS8237E-00 December 2012 |
www.richtek.com |
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RT8237E
Ordering Information
RT8237E
(2)
Pin 1 Orientation
(2) : Quadrant 2, Follow EIA-481-D
Package Type
QW : WDFN-10L 3x3 (W-Type)
Lead Plating System
Z : ECO (Ecological Element with Halogen Free and Pb free)
Note :
Richtek products are :
`RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`Suitable for use in SnPb or Pb-free soldering processes.
Pin Configurations
(TOP VIEW)
PGOOD 1 |
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10 |
BOOT |
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CS 2 |
GND |
9 |
UGATE |
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EN 3 |
8 |
PHASE |
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FB 4 |
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VCC |
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RF 5 |
11 6 |
LGATE |
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WDFN-10L 3x3
Marking Information
88 : Product Code
88 DF |
DFA26 : Date Code |
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A26 |
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Functional Pin Description
Pin No. |
Pin Name |
Pin Function |
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1 |
PGOOD |
Open Drain Power Good Indicator. High impedance indicates power is good. |
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2 |
CS |
Current Limit Threshold Setting Input. Connect a setting resistor to GND and the |
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current limit threshold is equal to 1/8 of the voltage at this pin. |
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EN |
Enable Control Input. Pull low to GND to disable the PWM. |
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4 |
FB |
VOUT Feedback Input. Connect FB to a resistor voltage divider from VOUT to GND |
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to adjust the output from 0.7V to 3.3V |
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Switching Frequency Selection. Connect a resistance to select switching |
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frequency as shown in Electrical Characteristics. The switching frequency is |
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5 |
RF |
detected and latched after startup. This pin also controls diode emulation mode or |
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forced CCM selection. |
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Pull down to GND with resistor : Diode Emulation Mode. |
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Connect to PGOOD with resistor : forced CCM after PGOOD becomes high. |
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6 |
LGATE |
Gate Drive Output for Low Side External MOSFET. |
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Supply Voltage Input. This pin provides the power for the Buck controller, the low |
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7 |
VCC |
side driver and the bootstrap circuit for high side driver. Bypass to GND with a 1μF |
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ceramic capacitor. |
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External Inductor Connection Pin for PWM Converter. It behaves as the current |
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8 |
PHASE |
sense comparator input for low side MOSFET RDS(ON) sensing and reference |
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voltage for on time generation. |
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9 |
UGATE |
Gate Drive Output for High Side External MOSFET. |
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10 |
BOOT |
Bootstrap Supply for High Side Gate Driver. Connect through a capacitor to the |
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floating node (PHASE). |
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11 |
GND |
Ground. The exposed pad must be soldered to a large PCB and connected to |
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(Exposed Pad) |
GND for maximum power dissipation. |
Copyright ©2012 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
www.richtek.com |
DS8237E-00 December 2012 |
2
RT8237E
Function Block Diagram
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TRIG |
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RF |
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On-time |
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Compute |
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BOOT |
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PHASE |
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-COMP |
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R |
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S |
Q |
PWM |
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UGATE |
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+ |
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DRV |
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VREF |
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Min. tOFF |
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PHASE |
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+ |
OV |
Latch |
Q |
TRIG |
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VCC |
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125% |
S1 |
Q |
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VREF |
- |
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Latch |
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DRV |
LGATE |
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FB |
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UV |
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70% |
S1 |
Q |
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GND |
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- |
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VREF |
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DEM/FCCM |
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125% VREF |
- |
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PGOOD |
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+ |
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VCC |
POR |
SS |
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- |
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Timer |
90% VREF |
+ |
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EN |
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Thermal |
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- |
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Shutdown |
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+ |
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X(1/8) |
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10µA |
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+ |
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- |
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X(-1/8) |
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CS |
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Copyright ©2012 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
DS8237E-00 December 2012 |
www.richtek.com |
3
RT8237E
Operation
The RT8237E integrates a Constant-On-Time (COT) PWM controller, and the controller provides the PWM signal which relies on the output ripple voltage comparing with internal reference voltage.
The UGATE driver is turned on at the beginning of each cycle. After the internal one-shot timer expires, the UGATE driver will be turned off. The pulse width of this one-shot is determined by the converter's input voltage and the output voltage to keep the frequency fairly constant over the input voltage and output voltage range.
Power On Reset, UVLO
Power On Reset (POR) occurs when VCC rises above to approximately 4.1V (typical), the RT8237E will reset the fault latch and prepare the PWM for operation. When the input voltage below 3.7V(min), the Under Voltage Lockout (UVLO) circuitry inhibits switching by keeping UGATE and LGATE low.
Soft-Start
The output voltage will track the internal ramp voltage during soft-start interval to prevent large inrush current and output voltage overshoot while the converter is being powered up.
Mode Selection
The RT8237E supports mode selection through the RF by connecting a resistor from the RF pin to either GND or PGOOD. When the resistor is connected to GND, the controller operates in diode emulation mode. When the resistor is connected to PGOOD, the controller operates in CCM mode.
Current Limit Setting
The RT8237E has a cycle-by-cycle current limit control. The current limit circuit employs a unique “valley” current sensing algorithm. If the magnitude of the sensing signal at PHASE is above the current limit threshold, the PWM is not allowed to initiate a new cycle.
Over Voltage Protection
The output voltage can be continuously monitored for over voltage condition. When the output voltage exceeds 25% of its set voltage threshold, the UGATE goes low and the LGATE is forced high.
Under Voltage Protection
The output voltage can be continuously monitored for under voltage condition. When the output voltage is less than 70% of its set voltage, under voltage protection is triggered and then both UGATE and LGATE gate drivers are forced low.
Copyright ©2012 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
www.richtek.com |
DS8237E-00 December 2012 |
4
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RT8237E |
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Absolute Maximum Ratings |
(Note 1) |
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z VCC, FB, PGOOD, EN, CS, RF to GND |
----------------------------------------------------------------------------- |
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−0.3V to 6V |
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z BOOT to PHASE ----------------------------------------------------------------------------------------------------------- |
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−0.3V to 6V |
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z PHASE to GND |
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DC ------------------------------------------------------------------------------------------------------------------------------ |
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−0.3V to 32V |
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<20ns ------------------------------------------------------------------------------------------------------------------------- |
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−8V to 38V |
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z UGATE to PHASE --------------------------------------------------------------------------------------------------------- |
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−0.3V to 6V |
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DC ------------------------------------------------------------------------------------------------------------------------------ |
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−0.3V to 6V |
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<20ns ------------------------------------------------------------------------------------------------------------------------- |
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−5V to 7.5V |
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z LGATE to GND -------------------------------------------------------------------------------------------------------------- |
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−0.3V to 6V |
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DC ------------------------------------------------------------------------------------------------------------------------------ |
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−0.3V to 6V |
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<20ns ------------------------------------------------------------------------------------------------------------------------- |
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−2.5V to 7.5V |
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z Power Dissipation, PD @ TA = 25°C |
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WDFN-10L 3x3 -------------------------------------------------------------------------------------------------------------- |
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3.28W |
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z Package Thermal Resistance (Note 2) |
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WDFN-10L 3x3, θJA -------------------------------------------------------------------------------------------------------- |
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30.5°C/W |
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WDFN-10L 3x3, θJC -------------------------------------------------------------------------------------------------------- |
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7.5°C/W |
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z Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------- |
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260°C |
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z Junction Temperature ------------------------------------------------------------------------------------------------------ |
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150°C |
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z Storage Temperature Range --------------------------------------------------------------------------------------------- |
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−65°C to 150°C |
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z ESD Susceptibility (Note 3) |
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HBM (Human Body Model) ----------------------------------------------------------------------------------------------- |
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2kV |
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Recommended Operating Conditions (Note 4) |
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z Input Voltage, VIN ---------------------------------------------------------------------------------------------------------- |
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4.5V to 26V |
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z Control Voltage, VCC ----------------------------------------------------------------------------------------------------- |
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4.5V to 5.5V |
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z Junction Temperature Range --------------------------------------------------------------------------------------------- |
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−40°C to 125°C |
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z Ambient Temperature Range --------------------------------------------------------------------------------------------- |
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−40°C to 85°C |
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Electrical Characteristics |
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(VCC = 5V, TA = 25°C, unless otherwise specified) |
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Parameter |
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Symbol |
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Test Conditions |
Min |
Typ |
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Max |
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Unit |
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Input Power Supply |
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VCC Quiescent Supply |
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IQ |
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FB |
forced above the |
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0.5 |
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1.25 |
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mA |
Current |
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point, VEN = 5V, |
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VCC Shutdown Current |
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ISHDN |
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VCC current, VEN = 0V |
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-- |
-- |
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1 |
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μA |
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CS Shutdown Current |
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CS pull to GND |
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-- |
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1 |
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μA |
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FB Error Comparator |
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VREF |
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DEM |
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0.7005 |
0.704 |
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0.7075 |
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V |
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Threshold |
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DEM, TA = −40 to 85°C |
(Note 5) |
0.697 |
0.704 |
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0.711 |
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FB Input Bias Current |
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VFB = 0.735V |
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−1 |
0.01 |
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1 |
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μA |
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Copyright ©2012 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
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DS8237E-00 December |
2012 |
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www.richtek.com |
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5 |
RT8237E
Parameter |
Symbol |
Test Conditions |
Min |
Typ |
Max |
Unit |
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VOUT Voltage Range |
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0.7 |
-- |
3.3 |
V |
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RRF = 470kΩ |
(Note 6) |
-- |
290 |
-- |
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Switching Frequency |
fSW |
RRF = 200kΩ |
(Note 6) |
-- |
340 |
-- |
kHz |
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RRF = 100kΩ |
(Note 6) |
-- |
380 |
-- |
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RRF = 39kΩ |
(Note 6) |
-- |
430 |
-- |
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Minimum Off-Time |
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250 |
400 |
550 |
ns |
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Current Sensing |
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CS Source Current |
ICS |
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9 |
10 |
11 |
μA |
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CS Source Current TC |
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-- |
4700 |
-- |
ppm/°C |
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Zero Crossing Threshold |
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DEM |
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−10 |
-- |
5 |
mV |
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GND − PHASE, VCS = 2.4V |
280 |
300 |
320 |
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Current Limit Threshold |
VLIM |
GND − PHASE, VCS = 1.6V |
185 |
200 |
215 |
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GND − PHASE, VCS = 0.4V |
40 |
50 |
60 |
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Negative Current Limit |
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PHASE − GND, VCS = 2.4V |
-- |
300 |
-- |
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PHASE − GND, VCS = 1.6V |
-- |
200 |
-- |
mV |
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Threshold |
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PHASE − GND, VCS = 0.4V |
-- |
50 |
-- |
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Protection Function |
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Output UV Threshold |
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With respect to error |
65 |
70 |
75 |
% |
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comparator threshold |
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OVP Threshold |
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With respect to error |
120 |
125 |
130 |
% |
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comparator threshold |
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OV Fault Delay |
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FB forced above OV threshold |
-- |
5 |
-- |
μs |
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VCC Under Voltage Lockout |
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Falling edge, |
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UVLO |
hysteresis = 100mV, PWM |
3.7 |
3.9 |
4.1 |
V |
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Threshold |
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disabled below this level |
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VOUT Soft-Start |
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From EN = high to VOUT = 95% |
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1300 |
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μs |
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UV Blank Time |
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From EN signal going high |
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3 |
-- |
ms |
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Thermal Shutdown |
TSD |
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-- |
150 |
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°C |
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Driver On Resistance |
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UGATE Drive Source |
RUGATEsr |
BOOT − PHASE forced to 5V |
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1.8 |
3.6 |
Ω |
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UGATE Drive Sink |
RUGATEsk |
BOOT − PHASE forced to 5V |
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1.2 |
2.4 |
Ω |
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LGATE Drive Source |
RLGATEsr |
LGATE, High State |
-- |
1.8 |
3.6 |
Ω |
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LGATE Drive Sink |
RLGATEsk |
LGATE, Low State |
-- |
0.8 |
1.6 |
Ω |
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Dead Time |
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LGATE Rising (VPHASE = 1.5V) |
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30 |
-- |
ns |
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UGATE Rising |
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-- |
30 |
-- |
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Internal Boost Charging Switch |
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VCC to BOOT, 10mA |
-- |
-- |
80 |
Ω |
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On Resistance |
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Copyright ©2012 Richtek Technology Corporation. All rights reserved. |
is a registered trademark of Richtek Technology Corporation. |
www.richtek.com |
DS8237E-00 December 2012 |
6
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