Fairchild Semiconductor FAN5234 Datasheet

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FAN5234

Mobile-Friendly PWM/PFM Controller

Features

• Wide input voltage range (2 to 24V) for Mobile systems

• Excellent dynamic response with Voltage Feed-Forward
and Average Current Mode control

• Lossless current sensing on low-side MOSFET or
precision over-current using sense resistor

• VCC Under-voltage Lockout

• Power-Good Signal

• Light load Hysteretic mode maximizes efficiency

• QSOP16, TSSOP16

• 300Khz or 600Khz operation

Applications

• Mobile PC regulator

• Hand-Held PC power

General Description

The FAN5234 PWM controller provides high efficiency and
regulation with an adjustable output from 0.9V to 5.5V that
are required to power I/O, chip-sets, memory banks or
peripherals in high-performance notebook computers, PDAs
and Internet appliances. Synchronous rectification and
hysteretic operation at light loads contribute to a high
efficiency over a wide range of loads. The hysteretic mode of
operation can be disabled if PWM mode is desired for all
load levels. Efficiency is even further enhanced by using
MOSFET’s R

Feed-forward ramp modulation, average current mode
control, and internal feedback compensation provide fast
response to load transients. The FAN5234 monitors these
outputs and generates a PGOOD (power good) signal when
the soft-start is completed and the output is within ±10% of
its set point. A built-in over-voltage protection prevents the
output voltage from going above 120% of the set point.
Normal operation is automatically restored when the over­voltage conditions go away. Under-voltage protection latches
the chip off when the output drops below 75% of its set value
after the soft-start sequence is completed. An adjustable
over-current function monitors the output current by sensing
the voltage drop across the lower MOSFET.

as a current sense component.

DS(ON)

Typical Application

VIN (BATTERY)

+5

+5 9

Figure 1. 1.8V Output Regulator (see Table 2, page 12 for BOM)

= 2 to 24V

C4

R5

C3

R4

PGOOD

VC

ILIM

EN

SS1

FPWM

AGND

VI

N

C

11

4

3

7

16

8

2

1

FAN5234

BOOT

Q1A

H

DRV

14

SW

13

Q1B

L

DRV

10

PGND

IS

NS

12

SEN

V

6

VOUT

5

C1

C5

R3

L1

D1

C2

+515

1.8V@3.5A

R1

C6

R2

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FAN5234 PRODUCT SPECIFICATION

Pin Configurations

VIN

PGOOD

ILIM

VOUT

VSEN

AGND

1
2

EN

3
4

FAN5234

5
6

SS

7
8

QSOP-16 or TSSOP-16

FPWM

16

BOOT

15

HDRV

14

SW

13

ISNS

12

VCC

11

LDRV

10

PGND

9

θJA = 112°C/W

Pin Definitions

Pin

Number Pin Name Pin Function Description

1 VIN

2 PGOOD Power Good Flag. An open-drain output that will pull LOW when VSEN is outside of a

3EN ENABLE . Enables operation when pulled to logic high. Toggling EN will also reset the

4 ILIM

5 VOUT

6 VSEN

7SS Soft Start. A capacitor from this pin to GND programs the slew rate of the converter

8 AGND

9 PGND

10 LDRV

11 VCC

12 ISNS

13 SW

14 HDRV

15 BOOT

16 FPWM Forced PWM mode. When logic HIGH, inhibits the regulator from entering hysteretic

Input Voltage. Connect to main input power source (battery). Also used to program

operating frequency for low input voltage operation. See Table 1.

±10% range of the 0.9V reference.

regulator after a latched fault condition. This is a CMOS inputs whose state is
indeterminate if left open.

Current Limit. A resistor from this pin to GND sets the current limit.

Output Voltage. Connect to output voltage. Used for regulation to ensure a smooth

transitions during mode changes. When VOUT is expected to exceed VCC, tie this pin to
VCC.

Output Voltage Sense. The feedback from the output. Used for regulation as well as

PGOOD, under-voltage, and over-voltage protection and monitoring.

during initialization. During initialization, this pin is charged with a 5 µ A current source.

Analog Ground. This is the signal ground reference for the IC. All voltage levels are

measured with respect to this pin.

Power Ground. The return for the low-side MOSFET driver. Connect to source of low-

side MOSFET.

Low-Side Drive. The low-side (lower) MOSFET driver output. Connect to gate of low-side

MOSFET.

VCC. This pin powers the chip as well as the LDRV buffers. The IC starts to operate when

voltage on this pin exceeds 4.6V (UVLO rising) and shuts down when it drops below 4.3V
(UVLO falling).

Current Sense input. Monitors the voltage drop across the lower MOSFET or external

sense resistor for current feedback.

Switching node. Return for the high-side MOSFET driver and a current sense input.

Connect to source of high-side MOSFET and low-side MOSFET drain.

High-Side Drive. High-side (upper) MOSFET driver output. Connect to gate of high-side

MOSFET.

BOOT. Positive supply for the upper MOSFET driver. Connect as shown in Figure 2.

mode.

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) –

FAN5234 PRODUCT SPECIFICATION

Absolute Maximum Ratings

Absolute maximum ratings are the values beyond which the device may be damaged or have its useful life
impaired. Functional operation under these conditions is not implied.

Parameter Min. Typ. Max. Units

VCC Supply Voltage: 6.5 V

VIN 27 V

BOOT, SW, ISNS, HDRV 33 V

BOOT to SW 6.5 V

All Other Pins –0.3 VCC+0.3 V

Junction Temperature (T

Storage Temperature –65 150 °C

Lead Soldering Temperature, 10 seconds 300 °C

) –10 150 °C

J

Recommended Operating Conditions

Parameter Conditions Min. Typ. Max. Units

Supply Voltage VCC

Supply Voltage VIN

Ambient Temperature (T

A

4.75 5 5.25 V

524V

10 85 °C

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PRODUCT SPECIFICATION FAN5234

µ

µ

µ

µ

µ

Ω

Ω

Ω

Ω

µ

Electrical Specifications

Parameter Conditions Min. Typ. Max. Units

Power Supplies

VCC Current LDRV, HDRV Open, VSEN forced

VIN Current - Sinking VIN pin = input voltage source 10 20 30

VIN Current - Sourcing VIN pin = GND 7 15 20

VIN Current - Shut-down 1

UVLO Threshold Rising VCC 4.3 4.55 4.75 V

Oscillator

Frequency VIN > 5V 255 300 345 KHz

Ramp Amplitude, pk–pk VIN = 16V 2 V

Ramp Amplitude, pk–pk VIN < 5V 1.25 V

Ramp Offset 0.5 V

Ramp / VIN Gain VIN >

Ramp / VIN Gain 1V < VIN < 3V 250 mV/V

Reference and Soft Start

Internal Reference Voltage 0.891 0.9 0.909 V

Soft Start current (I

Soft Start Complete Threshold 1.5 V

PWM Converter

Load Regulation I

VSEN Bias Current 50 80 120 nA

VOUT pin input impedance 40 55 65 K Ω

Under-voltage Shutdown as % of set point. 2 µ S noise filter 70 75 80 %

I

Over-Current threshold R

SNS

Over-voltage threshold as % of set point. 2 µ S noise filter 113 120 %

Output Driver

HDRV Output Resistance Sourcing 8 15

LDRV Output Resistance Sourcing 8 15

PGOOD (Power Good Output) and Control pins

Lower Threshold as % of set point, 2 µ S noise filter 86 92 %

Upper Threshold as % of set point, 2 µ S noise filter 110 115 %

PGOOD Output Low I

Leakage Current V

Soft Start Voltage when PGOOD
Enabled

EN, FPWM Inputs

Input High 2 V

Input Low 0.8 V

) at start-up 5

SS

Recommended operating conditions, unless otherwise noted.

850 1300 µ A

above regulation point

Shut-down (EN=0) 5 15

Falling 4.1 4.27 4.5 V

Hysteresis 0.1 0.5 V

VIN = 0V 510 600 690 KHz

3V 125 mV/V

from 0 to 3A, VIN from 2 to 24V -1 +1 %

OUT

= 68.5K Ω . See Figure 4 115 144 172 µA

ILIM

Sinking 3.2 4

Sinking 1.5 2.4

= 4mA 0.5 V

PGOOD

= 5V 1

PULLUP

1.5 V

A

A

A

A

A

A

4

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FAN5234 PRODUCT SPECIFICATION

5V

EN

FPWM

VIN

VSEN

VDD

POR/UVLO

FPWM

HYST

SS

OVP

OSC

CL

RAMP

K

Q

SR

PWM

EA

DUTY

CYCLE

CLAMP

RAMP

HYST

ADAPTIVE

GATE

CONTROL LOGIC

PWM

PWM /HYST

ILIM det.

CURRENT PROCESSING

I

Σ

OUT

VDD

S/H

MODE

BOOT

HDRV

SW

LDRV

PGND

ISNS

Q1

Q2

R

VIN

SENSE

C

BOOT

VOUT

L

OUT

C

OUT

SS

P

GOOD

REF2

Reference and

Soft Start

VREF

PWM/HYS

T

Figure 2. IC Block Diagram

Circuit Description

Overview

The FAN5234 is a PWM controller intended for low voltage
power applications in modern notebook, desktop, and
sub-notebook PCs. The output voltage of the controller can
be set in the range of 0.9V to 5.5V by an external resistor
divider.

The synchronous buck converter can operate from either an
unregulated DC source (such as a notebook battery) with
voltage ranging from 2V to 24V, or from a regulated system
rail. In either mode of operation the IC is biased from a +5V
source. The PWM modulator uses an average current mode
control with input voltage feed-forward for simplified feed­back loop compensation and improved line regulation. The
controller includes integrated feedback loop compensation
that dramatically reduces the number of external compo­nents.

Depending on the load level, the converter can operate either
in fixed frequency PWM mode or in a hysteretic mode.
Switch-over from PWM to hysteretic mode improves the
converters' efficiency at light loads and prolongs battery run
time. In hysteretic mode, a comparator is synchronized to the
main clock that allows seamless transition between the oper­ational modes and reduced channel-to-channel interaction.

ILIM

R

ILIM

The hysteretic mode of operation can be inhibited indepen­dently using the FPWM pin if variable frequency operation is
not desired.

Oscillator

Table 1. Converter Operating modes

Mode

F

SW

(Khz)

Converter

Power VIN Pin

Battery 300 2 to 24V Battery (>5V)

Fixed

300 < 5.5V Fixed 100K Ω to GND

300

Fixed

600 < 5.5V Fixed GND

600

When VIN is from the battery, the oscillator's ramp ampli­tude is proportional to VIN, providing voltage feed-forward
control for improved loop response. When in either of the
Fixed modes, oscillator's ramp amplitude is fixed. The oper­ating frequency is then determined according to the connec­tion on the VIN pin (Table 1).

Initialization and Soft Start

Assuming EN is high, FAN5234 is initialized when VCC
exceeds the rising UVLO threshold. Should VCC drop below
the UVLO threshold, an internal Power-On Reset function
disables the chip.

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