LM2635 datasheet(2/13 Pages) NSC

No de pièce	LM2635

Description	5-Bit Programmable Synchronous Buck Regulator Controller

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Fabricant	NSC [National Semiconductor (TI)]

Site Internet	http://www.national.com

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Connection Diagram

Pin Descriptions

LSGATE (Pin 1): Gate drive for the low-side N-channel

MOSFET. This signal is interlocked with HSGATE (Pin 20) to

avoid a shoot-through problem.

BOOTV (Pin 2): Power supply for high-side N-channel

MOSFET gate drive. The voltage should be at least one gate

threshold above the converter input voltage to properly oper-

ate the high-side N-FET.

PGND (Pin 3): Ground for high current circuitry. It should be

connected to system ground.

SGND (Pin 4): Ground for signal level circuitry. It should be

connected to system ground.

V

CC (Pin 5): Power supply for the controller.

SENSE (Pin 6): Converter output voltage sensing. It pro-

vides input for power good, fast dual comparator control

loop, and over-voltage protection circuitry. It is recom-

mended that a 0.1 µF capacitor be connected between this

pin and ground to avoid potential noise problems.

IMAX (Pin 7): Current limit threshold setting. It sinks a fixed

180 µA current. By connecting a resistor between the high

side MOSFET drain and this pin, a fixed voltage drop can be

built across the resistor. This voltage drop is compared with

the V

DS of the high-side N-MOSFET to determine if an over-

current condition has occurred.

IFB (Pin 8): High-side N-MOSFET source voltage sensing.

This pin is one V

DS below drain voltage. When this voltage is

lower than that of IMAX pin during the time the high-side FET

is on, it means V

DS is higher than the preset voltage across

the IMAX resistor, which can be interpreted as an over-

current condition.

V

REF (Pin 9): Bandgap reference voltage. This voltage is

mainly for use by other power supplies on the motherboard

which need a reference.

EA_OUT (Pin 10): Output of the error amplifier. The voltage

level on this pin is compared with an internally generated

ramp signal to determine the duty cycle. This pin is neces-

sary for compensating the primary control loop.

FB (Pin 11): Inverting input of the error amplifier. A pin nec-

essary for compensating the control loop.

FREQ_ADJ (Pin 12): Switching frequency adjustment.

Switching frequency can be adjusted by changing the

grounding resistance on this pin.

PWRGD (Pin 13): Power Good. There are two windows

around the DAC output voltage that are associated with

PWRGD pin, the ±10% window and the ±8% window. If

PWRGD is initially high (open drain state) and output voltage

travels out of ±10% window, PWRGD goes to low (low im-

pedance to ground). If PWRGD is initially low and output

voltage travels into the ±8% window and has stayed within

the window for at least 10 ms, PWRGD goes to high. A

PWRGD high means the output voltage is at least within the

±10% window whereas a PWRGD low indicates the output

voltage is definitely outside the ±8% window.

VID4:0 (Pins 14, 15, 16, 17, 18): Voltage Identification

Code. The five pins accept an open-ground pattern 5-bit bi-

nary code from outside the chip (typically from the CPU) for

generating the desired output voltage. Each VID pin is inter-

nally pulled up to V

CC via a 90 µA current source. Table 1

shows the code table.

OUTEN (Pin 19): Output Enable. The output voltage is dis-

abled when this pin is pulled low. It is internally pulled up to

V

CC via a 90 µA current source.

HSGATE (Pin 20): Gate drive for the high-side N-channel

MOSFET. This signal is interlocked with LSGATE (Pin 1) to

avoid a shoot-through problem.

TABLE 1. VID Code and DAC Output

V

ID4

V

ID3

V

ID2

V

ID1

V

ID0

Rated Output

Voltage (V)

01111

(#) (1.30)

01110

(#) (1.35)

01101

(#) (1.40)

01100

(#) (1.45)

01011

(#) (1.50)

01010

(#) (1.55)

01001

(#) (1.60)

01000

(#) (1.65)

00111

(#) (1.70)

00110

(#) (1.75)

00101

1.80

00100

1.85

00011

1.90

00010

1.95

00001

2.00

00000

2.05

11111

(shutdown)

11110

2.1

11101

2.2

11100

2.3

11011

2.4

11010

2.5

11001

2.6

11000

2.7

10111

2.8

10110

2.9

10101

3.0

TOP VIEW

DS100119-3

Plastic SO-20

Order Number LM2635M

See NS Package Number M20B

www.national.com

2

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