Richtek RT8237EZQW Schematic [ru]

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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

 

 

BOOT

 

 

 

PGOOD

UGATE

 

 

 

EN

PHASE

 

RF

 

 

 

CS

LGATE

 

 

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

 

1

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

 

10

BOOT

CS 2

GND

9

UGATE

EN 3

8

PHASE

 

FB 4

 

7

VCC

RF 5

11 6

LGATE

WDFN-10L 3x3

Marking Information

88 : Product Code

88 DF

DFA26 : Date Code

 

A26

 

Functional Pin Description

Pin No.

Pin Name

Pin Function

1

PGOOD

Open Drain Power Good Indicator. High impedance indicates power is good.

2

CS

Current Limit Threshold Setting Input. Connect a setting resistor to GND and the

current limit threshold is equal to 1/8 of the voltage at this pin.

 

 

3

EN

Enable Control Input. Pull low to GND to disable the PWM.

 

 

 

4

FB

VOUT Feedback Input. Connect FB to a resistor voltage divider from VOUT to GND

to adjust the output from 0.7V to 3.3V

 

 

 

 

Switching Frequency Selection. Connect a resistance to select switching

 

 

frequency as shown in Electrical Characteristics. The switching frequency is

5

RF

detected and latched after startup. This pin also controls diode emulation mode or

forced CCM selection.

 

 

 

 

Pull down to GND with resistor : Diode Emulation Mode.

 

 

Connect to PGOOD with resistor : forced CCM after PGOOD becomes high.

6

LGATE

Gate Drive Output for Low Side External MOSFET.

 

 

Supply Voltage Input. This pin provides the power for the Buck controller, the low

7

VCC

side driver and the bootstrap circuit for high side driver. Bypass to GND with a 1μF

 

 

ceramic capacitor.

 

 

External Inductor Connection Pin for PWM Converter. It behaves as the current

8

PHASE

sense comparator input for low side MOSFET RDS(ON) sensing and reference

 

 

voltage for on time generation.

9

UGATE

Gate Drive Output for High Side External MOSFET.

 

 

 

10

BOOT

Bootstrap Supply for High Side Gate Driver. Connect through a capacitor to the

floating node (PHASE).

 

 

11

GND

Ground. The exposed pad must be soldered to a large PCB and connected to

(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

Richtek RT8237EZQW Schematic

RT8237E

Function Block Diagram

 

 

 

TRIG

 

 

 

 

 

 

 

 

RF

 

 

 

On-time

 

 

 

 

 

 

 

 

 

 

Compute

 

 

 

 

 

 

 

BOOT

 

PHASE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

-COMP

 

R

 

 

 

 

 

 

 

 

 

 

S

Q

PWM

 

UGATE

 

 

 

 

 

+

 

 

DRV

 

 

 

 

 

 

 

 

 

 

 

 

VREF

 

 

 

Min. tOFF

 

 

 

PHASE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

+

OV

Latch

Q

TRIG

 

 

VCC

 

 

 

125%

S1

Q

 

 

 

 

 

 

 

 

VREF

-

 

Latch

 

 

 

 

DRV

LGATE

FB

 

 

+

UV

 

 

 

 

 

70%

S1

Q

 

 

 

 

 

GND

 

 

-

 

 

 

 

 

 

 

 

VREF

 

 

 

 

DEM/FCCM

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

125% VREF

-

 

 

 

 

 

PGOOD

 

 

 

 

 

 

+

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VCC

POR

SS

 

 

 

-

 

 

 

 

 

 

 

 

Timer

90% VREF

+

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

EN

 

 

 

 

Thermal

 

-

 

 

 

 

 

 

 

 

 

Shutdown

 

+

 

 

 

 

 

 

 

 

 

 

 

 

X(1/8)

 

 

 

 

 

10µA

 

 

 

 

 

 

 

+

 

 

 

 

 

 

 

 

 

 

 

-

 

 

 

 

 

 

 

 

 

 

 

 

X(-1/8)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CS

 

 

 

 

 

 

 

 

 

 

 

 

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

 

 

 

 

 

 

 

 

 

RT8237E

Absolute Maximum Ratings

(Note 1)

 

 

 

 

 

 

 

z VCC, FB, PGOOD, EN, CS, RF to GND

-----------------------------------------------------------------------------

 

 

 

 

 

−0.3V to 6V

z BOOT to PHASE -----------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

−0.3V to 6V

z PHASE to GND

 

 

 

 

 

 

 

 

 

 

 

 

DC ------------------------------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

−0.3V to 32V

<20ns -------------------------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

−8V to 38V

z UGATE to PHASE ---------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

−0.3V to 6V

DC ------------------------------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

−0.3V to 6V

<20ns -------------------------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

−5V to 7.5V

z LGATE to GND --------------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

−0.3V to 6V

DC ------------------------------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

−0.3V to 6V

<20ns -------------------------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

−2.5V to 7.5V

z Power Dissipation, PD @ TA = 25°C

 

 

 

 

 

 

 

 

 

WDFN-10L 3x3 --------------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

3.28W

 

z Package Thermal Resistance (Note 2)

 

 

 

 

 

 

 

 

 

WDFN-10L 3x3, θJA --------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

30.5°C/W

WDFN-10L 3x3, θJC --------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

7.5°C/W

 

z Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------------

 

 

 

 

 

 

260°C

 

z Junction Temperature ------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

150°C

 

z Storage Temperature Range ---------------------------------------------------------------------------------------------

 

 

 

 

 

 

−65°C to 150°C

z ESD Susceptibility (Note 3)

 

 

 

 

 

 

 

 

 

HBM (Human Body Model) -----------------------------------------------------------------------------------------------

 

 

 

 

 

 

2kV

 

Recommended Operating Conditions (Note 4)

 

 

 

 

 

 

z Input Voltage, VIN ----------------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

4.5V to 26V

z Control Voltage, VCC -----------------------------------------------------------------------------------------------------

 

 

 

 

 

 

 

 

 

4.5V to 5.5V

z Junction Temperature Range ---------------------------------------------------------------------------------------------

 

 

 

 

 

 

−40°C to 125°C

z Ambient Temperature Range ---------------------------------------------------------------------------------------------

 

 

 

 

 

 

−40°C to 85°C

Electrical Characteristics

 

 

 

 

 

 

 

 

 

(VCC = 5V, TA = 25°C, unless otherwise specified)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Parameter

 

Symbol

 

 

Test Conditions

Min

Typ

 

Max

 

Unit

Input Power Supply

 

 

 

 

 

 

 

 

 

 

 

 

VCC Quiescent Supply

 

IQ

 

FB

forced above the

regulation

--

0.5

 

1.25

 

mA

Current

 

 

point, VEN = 5V,

 

 

 

 

 

 

 

 

 

 

 

 

 

VCC Shutdown Current

 

ISHDN

 

VCC current, VEN = 0V

 

--

--

 

1

 

μA

 

 

 

 

 

 

 

 

 

 

 

 

CS Shutdown Current

 

 

 

CS pull to GND

 

--

--

 

1

 

μA

 

 

 

 

 

 

 

 

 

 

 

 

FB Error Comparator

 

VREF

 

DEM

 

0.7005

0.704

 

0.7075

 

V

Threshold

 

 

DEM, TA = −40 to 85°C

(Note 5)

0.697

0.704

 

0.711

 

 

 

 

 

 

 

FB Input Bias Current

 

 

 

VFB = 0.735V

 

−1

0.01

 

1

 

μA

 

 

 

 

 

 

 

 

 

 

 

 

 

Copyright ©2012 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS8237E-00 December

2012

 

 

 

 

 

 

 

 

www.richtek.com

 

 

 

 

 

 

 

 

 

 

 

 

5

RT8237E

Parameter

Symbol

Test Conditions

Min

Typ

Max

Unit

VOUT Voltage Range

 

 

 

0.7

--

3.3

V

 

 

RRF = 470kΩ

(Note 6)

--

290

--

 

Switching Frequency

fSW

RRF = 200kΩ

(Note 6)

--

340

--

kHz

RRF = 100kΩ

(Note 6)

--

380

--

 

 

 

 

 

RRF = 39kΩ

(Note 6)

--

430

--

 

Minimum Off-Time

 

 

 

250

400

550

ns

 

 

 

 

 

 

 

 

Current Sensing

 

 

 

 

 

 

 

CS Source Current

ICS

 

 

9

10

11

μA

CS Source Current TC

 

 

 

--

4700

--

ppm/°C

 

 

 

 

 

 

 

 

Zero Crossing Threshold

 

DEM

 

−10

--

5

mV

 

 

 

 

 

 

 

 

 

GND − PHASE, VCS = 2.4V

280

300

320

 

Current Limit Threshold

VLIM

GND − PHASE, VCS = 1.6V

185

200

215

mV

 

 

GND − PHASE, VCS = 0.4V

40

50

60

 

Negative Current Limit

 

PHASE − GND, VCS = 2.4V

--

300

--

 

 

PHASE − GND, VCS = 1.6V

--

200

--

mV

Threshold

 

 

PHASE − GND, VCS = 0.4V

--

50

--

 

 

 

 

Protection Function

 

 

 

 

 

 

 

Output UV Threshold

 

With respect to error

65

70

75

%

 

comparator threshold

 

 

 

 

 

 

OVP Threshold

 

With respect to error

120

125

130

%

 

comparator threshold

 

 

 

 

 

 

OV Fault Delay

 

FB forced above OV threshold

--

5

--

μs

 

 

 

 

 

 

 

 

VCC Under Voltage Lockout

 

Falling edge,

 

 

 

 

 

UVLO

hysteresis = 100mV, PWM

3.7

3.9

4.1

V

Threshold

 

disabled below this level

 

 

 

 

 

 

 

 

 

 

VOUT Soft-Start

 

From EN = high to VOUT = 95%

--

1300

--

μs

UV Blank Time

 

From EN signal going high

--

3

--

ms

 

 

 

 

 

 

 

 

Thermal Shutdown

TSD

 

 

--

150

--

°C

Driver On Resistance

 

 

 

 

 

 

 

 

 

 

 

 

 

 

UGATE Drive Source

RUGATEsr

BOOT − PHASE forced to 5V

--

1.8

3.6

Ω

UGATE Drive Sink

RUGATEsk

BOOT − PHASE forced to 5V

--

1.2

2.4

Ω

 

 

 

 

 

 

 

LGATE Drive Source

RLGATEsr

LGATE, High State

--

1.8

3.6

Ω

 

 

 

 

 

 

 

LGATE Drive Sink

RLGATEsk

LGATE, Low State

--

0.8

1.6

Ω

Dead Time

 

LGATE Rising (VPHASE = 1.5V)

--

30

--

ns

 

 

 

 

 

 

 

UGATE Rising

 

--

30

--

 

 

 

 

 

 

 

 

 

 

 

 

Internal Boost Charging Switch

 

VCC to BOOT, 10mA

--

--

80

Ω

On Resistance

 

 

 

 

 

 

 

 

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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