Richtek RT8238A Manual

Single synchronous buck pwm controller

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Single Synchronous Buck PWM Controller
General Description
The RT8238A 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 RT8238A 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 Audio Skipping Mode (ASM)
setting maintains the switching frequency above 25kHz,
which eliminates noise in audio applications. The buck
conversion allows this device to directly step down high
voltage batteries at the highest possible efficiency. The
RT8238A is intended for CPU core, chipset, DRAM, or
other low voltage supplies as low as 0.5V. The RT8238A
is available in a WQFN-12L 2x2 package.
Ordering Information
RT8238A
Package Type
QW : WQFN-12L 2x2 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Z : ECO (Ecological Element with
Halogen Free and Pb free)
Note :
Richtek products are :
RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
©
Copyright
2014 Richtek Technology Corporation. All rights reserved.
DS8238A-07 January 2014
®
Features
Applications
Pin Configurations
Built in 1% 0.5V Reference Voltage
Adjustable 0.5V to 3.3V Output Range
Quick Load Step Response within 100ns
4700ppm/° ° ° ° ° C Programmable Current Limit by Low
Side R
Sensing
DS(ON)
4.5V to 26V Battery Input Range
Resistor Programmable Frequency
Internal Ramp Current Limit Soft-Start Control
Drives Large Synchronous Rectifier FETs
Integrated Boost Switch
Over/Under Voltage Protection
Thermal Shutdown
Power Good Indicator
RoHS Compliant and Halogen Free
Notebook Computers
CPU Core Supply
Chipset/RAM Supply as Low as 0.5V
Generic DC/DC Power Regulator
(TOP VIEW)
12
LGATE
1
PHASE
2
UGATE
3
4
WQFN-12L 2x2
is a registered trademark of Richtek Technology Corporation.
RT8238A
11
10
PGOOD
9
GND
EN
8
13
MODE
7
5
6
www.richtek.com
1

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Summary of Contents for Richtek RT8238A

  • Page 1 The RT8238A is intended for CPU core, chipset, DRAM, or Pin Configurations other low voltage supplies as low as 0.5V. The RT8238A (TOP VIEW) is available in a WQFN-12L 2x2 package. Ordering Information...
  • Page 2: Marking Information

    Pull up to 5V for Diode Emulation Mode (DEM). PWM Chip Enable. Pull low to GND to disable the PWM. © Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com RT8238A-07 January 2014...
  • Page 3: Function Block Diagram

    125% V LGATE Latch 70% V DEM/FCCM /ASM MODE 125% V PGOOD Timer 90% V Thermal 10µA Shutdown X(-1/10) © Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. RT8238A-07 January 2014 www.richtek.com...
  • Page 4: Absolute Maximum Ratings

    Control Voltage, V ------------------------------------------------------------------------------------------------------- 4.5V to 5.5V Junction Temperature Range --------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range --------------------------------------------------------------------------------------------- −40°C to 85°C © Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com RT8238A-07 January 2014...
  • Page 5: Electrical Characteristics

    UGATE Low State Ω LGATE Driver Source LGATE High State LGATEsr Ω LGATE Driver Sink LGATE Low State LGATEsk © Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. RT8238A-07 January 2014 www.richtek.com...
  • Page 6 Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. © Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com RT8238A-07 January 2014...
  • Page 7: Typical Operating Characteristics

    CCM Mode DEM Mode CCM Mode, V = 1V, No Load 0.001 0.01 Load Current (A) Input Voltage (V) © Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. RT8238A-07 January 2014 www.richtek.com...
  • Page 8 (20V/Div) (10V/Div) LGATE (5V/Div) (500mV/Div) (10A/Div) (10A/Div) (50mV/Div) = 12V, V = 1V, No Load Time (20μs/Div) Time (20μs/Div) © Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com RT8238A-07 January 2014...
  • Page 9 (5V/Div) = 12V, V = 1V, No Load = 12V, V = 1V, No Load Time (1ms/Div) Time (1ms/Div) © Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. RT8238A-07 January 2014 www.richtek.com...
  • Page 10: Application Information

    PWMs while MODE pin to a logic high level. The RT8238A can switch avoiding the problems caused by widely varying switching operation into DEM when the MODE pin is pulled up to frequencies in conventional constant on-time and constant 5V.
  • Page 11 (Figure 2). In order to provide both good inductor value. Generally, low inductor values produce a accuracy and a cost effective solution, the RT8238A broader efficiency vs. load curve, while higher values result supports temperature compensated MOSFET R...
  • Page 12 On Reset (POR) occurs when VCC rises above to DS(ON) driver, 5V bias voltage is delivered from the VDDP supply. approximately 3.9V, the RT8238A will reset the fault latch The average drive current is proportional to the gate charge and preparing the PWM for operation.
  • Page 13 The required power dissipation depends on the thermal resistance of © Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. RT8238A-07 January 2014 www.richtek.com...
  • Page 14 (s) and shield the feedback trace from power traces θ resistance, . For the RT8238A package, the derating and components. curve in Figure 5 allows the designer to see the effect of Current sense connections must always be made using...
  • Page 15: Outline Dimension

    Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use.

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