Richtek RT8237EZQW Schematic [ru]

RT8237E

High Efficiency Single Synchronous Buck PWM Controller

General Description

The RT8237E PWM controller provides high efficiency, excellent transient response, a nd high DC output a ccuracy 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 ha ndles wide input/output voltage ratios with ea se and provides 100ns “instant-on” response to load transients while maintaining a relatively constant switching frequency .

The RT8237E achieves high ef ficiency 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

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 R T8237E is available in the WDFN-10L 3x3 pa ckage.

efficiency. The pre-set frequency selections

Features

z Wide Input Voltage Range : 4.5V to 26V z Output Voltage Range : 0.7V to 3.3V z Built-in 0.5% 0.7V Reference Voltage z Quick Load-Step Response within 100ns z 4700ppm/

DS(ON)

z Adjustable Current Limit with Low Side MOSFET z 4 Selectable Frequency Setting z Soft-Start Control z Drives Large Synchronous-Rectifier FET s z Integrated Boot Switch z Built-in OVP/OCP/UVP z Thermal Shutdown z Power Good Indicator z RoHS Compliant and Halogen Free

°°

°C Current Source for Current Limit

°°

Applications

z Notebook Computers z CPU Core Supply z Chipset/RAM Supply a s Low as 0.7V z Generic DC/DC Power Regulator

Simplified Application Circuit

DS8237E-00 December 2012 www.richtek.com

EN RF

OUT

RT8237E

Ordering Information

RT8237E

(2)

Pin Configurations

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 require-

ments of IPC/JEDEC J-STD-020.

` Suitable for use in SnPb or Pb-free soldering processes.

Marking Information

88 DF

A26

Functional Pin Description

Pin No. Pin Name Pi n Fun cti o n

1 PGOOD Open Drain Power Good Indicator. High impedance indicates power is good. 2 CS 3 EN Enable Control Input. Pull low to GND to disable the PWM. 4 FB

5 RF

6 LGATE Gate Drive Output for Low Side External MOSFET.

7 VCC

8 PHASE

9 UGATE Gate Drive Output for High Side External MOSFET.

10 BOOT

(Exposed Pad)

GND

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.

Feedback Input. Connect FB to a resistor voltage divider from V

OUT

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 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.

Supply Voltage Input. This pin provides the power for the Buck controller, the low 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 sense comparator input for low side MOSFET R voltage for on time generation.

Bootstrap Supply for High Side Gate Driver. Connect through a capacitor to the floating node (PHA SE).

Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation.

(TOP VIEW)

PGOOD

1 2

WDFN-10L 3x3

88 : Product Code DFA26 : Date Code

DS(ON)

BOOT

UGATE

PHASE

GND

VCC

LGATE

to GND

OUT

sensing and reference

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Function Block Diagram

TRIG

PHASE

On-time

Compute

COMP

RT8237E

BOOT

PWM

DRV

UGATE

VCC

POR

10µA

125%

REF

70%

REF

Timer

REF

125% V

90% V

Latch

S1 Q

Latch

S1 Q

REF

Thermal

Shutdown

Min. t

OFF

QTRIG

DEM/FCCM

X(1/8)

X(-1/8)

VCC

DRV

PHASE

LGATE GND

PGOOD

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RT8237E

Operation

The RT8237E integrates a Constant-On-T ime (COT) PWM controller, and the controller provides the PWM signal which relies on the output ripple voltage comparing with internal reference voltage.

The UGA TE driver is turned on at the beginning of each cycle. After the internal one-shot ti mer expires, the UGA TE 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 ra nge.

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 UGA TE and LGA TE low.

Soft-Start

Mode Selection

The RT8237E supports mode selection through the RF by connecting a resistor from the RF pin to either G ND 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 UGA TE goes low and the LGA TE is forced high.

The output voltage will track the internal ra mp voltage during soft-start interval to prevent large inrush current and output voltage overshoot while the converter is being powered up.

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 UGA TE a nd LGATE gate drivers are f orced low.

DS8237E-00 December 2012www.richtek.com

RT8237E

Absolute Maximum Ratings (Note 1)

z VCC, FB, PGOOD, EN, CS, RF to GN D ----------------------------------------------------------------------------- −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 UGA TE to PHASE --------------------------------------------------------------------------------------------------------- −0.3V to 6V

DC------------------------------------------------------------------------------------------------------------------------------ −0.3V to 6V <20ns ------------------------------------------------------------------------------------------------------------------------- −5V to 7.5V

z LGA TE t o G ND -------------------------------------------------------------------------------------------------------------- −0.3V to 6V

z Power Dissipation, P

W D FN-10L 3x3-------------------------------------------------------------------------------------------------------------- 3.28W

z Package Thermal Resistance (Note 2)

W DFN-10L 3x3, θJA-------------------------------------------------------------------------------------------------------- 30.5°C/W WDFN-10L 3x3, θJC-------------------------------------------------------------------------------------------------------- 7.5°C/W

z Lead T e mperature (Soldering, 10 sec.)-------------------------------------------------------------------------------- 260 °C z Junction T emperature------------------------------------------------------------------------------------------------------ 150°C z Storage T emperature Range --------------------------------------------------------------------------------------------- −65°C to 150°C z ESD Susceptibility (Note 3)

HBM (Human Body Model)----------------------------------------------------------------------------------------------- 2kV

@ TA = 25°C

Recommended Operating Conditions (Note 4)

z Input V oltage, VIN ---------------------------------------------------------------------------------------------------------- 4.5V to 26V z Control Voltage, VCC----------------------------------------------------------------------------------------------------- 4.5V to 5.5V z Junction T emperature Range--------------------------------------------------------------------------------------------- −40°C to 125°C z Ambient T emperature Range--------------------------------------------------------------------------------------------- −40°C to 85°C

Electrical Characteristics

(VCC = 5V, T

Input Power Supply

VCC Quiescent Supply Current

VCC Shutdown Current I CS Shutdo wn Current CS pull to GND -- -- 1 μA

FB Error Comparator Threshold

FB In put Bias Current V

= 25°C, unless otherwise specified)

Parameter Symbol Test Conditions Min Typ Max Unit

SHDN

FB forced above the regulation point, V

= 5V,

VCC current, VEN = 0V -- -- 1 μA

-- 0.5 1.25 mA

DEM 0.7005 0.704 0.7075

REF

DEM, T

= −40 to 85°C (Note 5) 0.697 0.704 0.711

= 0.735V −1 0.01 1 μA

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RT8237E

Parameter Symbol Test Conditions Min Typ Max Unit

Voltage Range 0.7 -- 3.3 V

OUT

RRF = 470kΩ (Note 6) -- 290 --

Switching Frequency f

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 T C -- 4700 -- ppm/°C Zero Crossing Threshold DEM −10 -- 5 mV

RRF = 200kΩ (Note 6) -- 340 --

Current Limit Threshold V

LIM

GND − PHASE, V GND − PHASE, VCS = 1.6V 185 200 215

= 2.4V 280 300 320

GND − PHASE, VCS = 0.4V 40 50 60

PHASE − GND, VCS = 2.4V -- 300 --

Negative Current Limit Threshold

PHASE − GND, VCS = 1.6V -- 200 - PHASE − GND, V

= 0.4V -- 50 --

Protection Function

Output UV Threshold

OVP Threshold

With respect to error comparator threshold With respect to error comparator threshold

65 70 75 %

120 125 130 % OV Fault Delay FB forced above OV threshold -- 5 -- μs VCC Under Voltage Lockout

Threshold V

Soft-Start From EN = high to V

OUT

UVLO

Falling edge, hysteresis = 100mV, PWM disabled below this level

= 95% -- 1300 -- μs

OUT

3.7 3.9 4.1 V

UV Blank Time From EN signal going high -- 3 -- ms Thermal Shutdown TSD -- 150 -- °C

Driver On Resistance

UGATE Dri ve Source R UGATE Dri ve Sink R LGATE Drive Source R LGATE Drive Sink R

Dead Time

UGATEsr UGATEsk LGATEsr LGATEsk

LGATE Rising (V

BOOT − PHASE forced to 5V -- 1.8 3.6 Ω

BOOT − PHASE forced to 5V -- 1.2 2.4 Ω

LGATE, High State -- 1.8 3.6 Ω

LGATE, Low State -- 0.8 1.6 Ω

= 1.5V) -- 30 --

PHASE

UGATE Rising -- 30 --

Internal Boost Charging Swi tch On Resistance

VCC to BOOT, 10mA -- -- 80 Ω

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