Fairchild Semiconductor RC5054AM Datasheet

Alpha is a trademark of Digital Equipment Corporation. Pentium is a registered trademark of Intel Corporation. PowerPC is a trademark of IBM
Corporation.

www.fairchildsemi.com

Rev. 1.0.2

Features

• Drives Two N-Channel MOSFETs

• Operates from +5V Power Input

• Simple Single-Loop Control Design

- Voltage-Mode PWM Control

• Fast Transient Response

- High-Bandwidth Error Amplifier

- Full 0% to 100% Duty Ratio

• Excellent Output Voltage Regulation

• TTL Compatible 5 Bit Digital-to-Analog Output Voltage
Selection

- Wide Range - 1.3V

DC

to 3.5V

DC

- 0.1V Binary Steps from 2.1V

DC

to 3.5V

DC

- 0.05V Binary Steps from 1.3V

DC

to 2.1V

DC

• Power-Good Output Voltage Monitor

• Over-Voltage and Over-Current Fault Monitors

- Does Not Require Extra Current Sensing Element, Uses

MOSFET’s R

DS(ON)

• Small Converter Size

- Constant Frequency Operation

- 200kHz Free-Running Oscillator Programmable from

50kHz to 1MHz

Applications

• Power Supply for Pentium

®

, Pentium Pro, PowerPC™

and Alpha™ Microprocessors

• High-Power 5V to 3.xV DC-DC Regulators

• Low-Voltage Distributed Power Supplies

Description

The RC5054A provides complete control and protection for
a DC-DC converter optimized for high-performance micro­processor applications. It is designed to drive two N-Channel
MOSFETs in a synchronous-rectified buck topology. The
RC5054A integrates all of the control, output adjustment,
monitoring and protection functions into a single package.

The output voltage of the converter is easily adjusted and
precisely regulated. The RC5054A includes a 5-input digital­to-analog converter (DAC) that adjusts the output voltage
from 2.1V

DC

to 3.5V

DC

in 0.1V increments and from

1.3V

DC

to 2.1V

DC

in 0.05V steps.

The RC5054A provides simple, single feedback loop, volt-

RC5054A

Programmable Synchronous DC-DC Converter
Controller for Low Voltage Microprocessors

Block Diagram

D/A

CONVERTER

(DAC)

OSCILLATOR

SOFT-

START

REFERENCE

POWER-ON

RESET (POR)

115%

110%

90%

INHIBIT

PWM

COMPARATOR

ERROR

AMP

VCC

PGOOD

SS

PWM

OVP

RT

GND

VSEN

OCSET

VID0
VID1
VID2
VID3

FB

COMP

DACOUT

OVER-

VOLTAGE

OVER-

CURRENT

GATE

CONTROL

LOGIC

BOOT
UGATE

PHASE

200µA

10µA

4V

+

-

+

-

+

-

+

-

+

-

+

-

VID4

LGATE
PGND

RC5054A PRODUCT SPECIFICATION

2

age-mode control with fast transient response. It includes a
200KHz free-running triangle-wave oscillator that is adjust­able from 50KHz to 1MHz. The error amplifier features a
15MHz gain-bandwidth product and 6V/ µ s slew rate which
enables high converter bandwidth for fast transient perfor­mance. The resulting PWM duty ratio ranges from 0% to
100%.

The RC5054A monitors the output voltage with a window
comparator that tracks the DAC output and issues a Power
Good signal when the output is within ± 10%. The RC5054A
protects against over-current conditions by inhibiting PWM
operation. Built-in over-voltage protection triggers an exter­nal SCR to crowbar the input supply. The RC5054A moni­tors the current by using the R

DS(ON)

of the upper MOSFET

which eliminates the need for a current sensing resistor.

Pin Assignments

VSEN

OCSET

SS
VID0
VID1
VID2

VID4

VID3

COMP

FB

RT

VCC
LGATE
PGND

OVP

BOOT
UGATE
PHASE
PGOOD
GND

RC5054

(SOIC)

TOP VIEW

11

12

13

14

15

16

17

18

20
19

10

9

8

7

6

5

4

3

2

1

Pin Definitions

Pin Number Pin Names Pin Function Description

1 VSEN This pin is connected to the converter’s output voltage. The PGOOD and OVP

comparator circuits use this signal to report output voltage status and for overvoltage
protection.

2 OCSET Connect a resistor (R

OCSET

) from this pin to the drain of the upper MOSFET.

R

OCSET

, an internal 200 µ A current source (I

OCS

), and the upper MOSFET on-

resistance (R

DS(ON)

) set the converter over-current (OC) trip point according to the

following equation:

An over-current trip cycles the soft-start function.

3 SS Connect a capacitor from this pin to ground. This capacitor, along with an internal

10 µ A current source, sets the soft-start interval of the converter.

4-8 VID0-VID4 VID0-4 are the input pins to the 5-bit DAC. The states of these five pins program the

internal voltage reference (DACOUT). The level of DACOUT sets the converter
output voltage. It also sets the PGOOD and OVP thresholds. Table 1 specifies
DACOUT for the 32 combinations of DAC inputs.

9 COMP COMP and FB are the available external pins of the error amplifier. The FB pin is the

inverting input of the error amplifier and the COMP pin is the error amplifier output.
These pins are used to compensate the voltage-control feedback loop of the
converter.

10 FB

11 GND Signal ground for the IC. All voltage levels are measured with respect to this pin.
12 PGOOD PGOOD is an open collector output used to indicate the status of the converter

output voltage. This pin is pulled low when the converter output is not within ± 10% of
the DACOUT reference voltage.

13 PHASE Connect the PHASE pin to the upper MOSFET source. This pin is used to monitor

the voltage drop across the MOSFET for over-current protection. This pin also
provides the return path for the upper gate drive.

14 UGA TE Connect UGATE to the upper MOSFET gate. This pin provides the gate drive for the

upper MOSFET.

15 BOOT This pin provides bias voltage to the upper MOSFET driver. A bootstrap circuit may

be used to create a BOOT voltage suitable to drive a standard N-Channel MOSFET.

16 PGND This is the power ground connection. Tie the lower MOSFET source to this pin.

I

PEAK

I

OCSROCSET

•

R

DS ON()

----------------------------------------=

PRODUCT SPECIFICATION RC5054A

3

Absolute Maximum Ratings

Recommended Operating Conditions

Thermal Characteristics

NOTE:

1.

θ

JA

is measured with the component mounted on an evaluation PC board in free air.

17 LGATE Connect LGATE to the lower MOSFET gate. This pin provides the gate drive for the

lower MOSFET.
18 VCC Provide a 12V bias supply for the chip to this pin.
19 OVP The OVP pin can be used to drive an external SCR in the event of an overvoltage

condition.
20 RT This pin provides oscillator switching frequency adjustment. By placing a resistor

(R

T

) from this pin to GND, the nominal 200KHz switching frequency is increased

according to the following equation:

Conversely, connecting a pull-up resistor (RT) from this pin to VCC reduces the

switching frequency according to the following equation:

Min. Max.

Power Input Voltage, V

IN

6V

Supply Voltage, V

CC

+13.5V

Boot Voltage, V

BOOT

- V

PHASE

+13.5V

V

CC

or I/O Voltage GND -0.3V V

CC

+ 0.3V

ESD Classification Class 2

Min. Max.

Supply Voltage, V

CC

+12V -10% +12V +10%
Ambient Temperature Range 0 ° C 70 ° C
Junction Temperature Range 0 ° C 125 ° C

Parameter Conditions Min. Typ. Max. Units

Thermal Resistance

1

θ

JA

SOIC Package
SOIC Package With 3in

2

of Copper

110

86

°

C/W

°

C/W

Maximum Junction Temperature Plastic Package 150

°

C

Maximum Storage Temperature Range -65 150

°

C

Maximum Lead Temperature Soldering 10s 300

°

C

Pin Definitions

(continued)

Pin Number Pin Names Pin Function Description

S

200kHz

3.5 10

6

× KHz x Kohm[]

R

T

Kohm[]

------------------------------------------------------------+= R

T

to GND(

)

FS200kHz

310

5

× KHz x Kohm[]

R

T

Kohm[]

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

–= R

T

to 12V()

RC5054A PRODUCT SPECIFICATION

4

Electrical Specifications

(Recommended Operating Conditions unless otherwise specified)

Symbol Parameter Test Conditions Min. Typ. Max. Units

VCC Supply Current

I

CC

Nominal Supply UGATE and LGATE Open – 22 – mA

Power-On Reset

Rising VCC Threshold V

OCSET

= 4.5V – – 10.4 V

Falling VCC Threshold V

OCSET

= 4.5V 8.8 – – V

Rising V

OCSET

Threshold – 1.26 – V

Oscillator

Free Running Frequency RT = OPEN 185 200 215 KHz

∆

V

OSC

Ramp Amplitude RT = Open – 1.9 – V

P-P

Reference and DAC

Initial Voltage Setpoint I

LOAD

= 0.8A, V

OUT

= 2.000V

V

OUT

= 1.550V

1.980

1.534

2.000

1.550

2.020

1.566VV

Error Amplifier

DC Gain – 88 – dB

GBW Gain-Bandwidth Product – 15 – MHz

SR Slew Rate COMP = 10pF – 6 – V/ µ s

Gate Drivers

I

UGATE

Upper Gate Source V

BOOT

- V

PHASE

= 12V 350 500 – mA

I

UGATE

Upper Gate Sink V

UGATE

- V

PHASE

= 1V – 100 – mA

I

LGATE

Lower Gate Source V

CC

= 12V, V

LGATE

= 6V 300 450 – mA

I

LGATE

Lower Gate Sink V

UGATE

- V

PHASE

= 1V – 100 – mA

Protection

Over-Voltage Trip (V

SEN

/DACOUT) – 115 120 %

I

OCSET

OCSET Current Source V

OCSET

= 4.5V

DC

170 200 230 µA

I

OVP

OVP Sourcing Current V

SEN

= 5.5V, V

OVP

= 0V 60 – – mA

I

SS

Soft Start Current – 10 – µA

Power Good

Upper Threshold (V

SEN

/DACOUT) VSEN Rising 106 – 111 %

Lower Threshold (V

SEN

/DACOUT) VSEN Falling 89 – 94 %

Hysteresis (V

SEN

/DACOUT) Upper and Lower Threshold – 2 – %

V

PGOOD

PGOOD Voltage Low I

PGOOD

= -5mA – 0.5 – V