RT9643

2

DS9643-03 August 2007

www.richtek.com

Typical Application Circuit

Operation

The RT9643 provides 5 functions:

1. A general purpose PWM regulator, used to generate VDDQ power for DDR memory.

2. A source-sink linear VTT regulator capable of sinking and sourcing 1.5A peak(minimum).

3. An adjustable Low Drop Out controller which, in conjunction with an external N-Channel power MOSFET, provides a

programmable low voltage output. It normally provides 1.2V for GTL FSB termination voltage.

4. Generating a 5V DUAL voltage using an external N-channel to supply power from 5V MAIN in S0, and an external

P-Channel to provide power from 5V Standby (5VSB) in S3.

5.An internal LDO which regulates “3V DUAL” in S3 mode from VCC(VSB). In S3, this regulator is capable of 1.25A

peak currents with current limit protection (2A typ.).

100k

good will output voltage with 3ms delay time.

When the output voltage falling arrive 75% of normal value the power good will turn off with less than 1ms delay time.

falling arrive POR value (4V typ.) the power good also will turn off quickly.

Q1

Q2

C1

RT9643

VCC_EN

PGOOD

PHASE

5V_MAIN

LGATE

ISNS

GND

VCC

16

3

4

9

10

19,

Exposed Pad (25)

L1

BOOT

ILIM

SS

3VSB_OUT

17

8

23

Q3

5VSB_DRV

1.2V_FB

15

1.2V_DRV

R3

R1

R6

C5

C9

C6

R2

R9

C11

C10

R10

C8

C7

C2

12V

R4

5V_MAIN

5V DUAL

Q4

5VSB

3.3 MAIN

Q5

C12

R7

R8

Q6

1.2 OUT

C17

VDDQ

5VSB

C4

C3

R5

L2

UGATE

FB

COMP

VDDQ_IN

VTT_SNS

REF_IN

VTT_OUT

EN

Chip Enable

S3#I

>

11

12

22

7

5

24

6

18

13

20

21

14

1

2

C13

3V DUAL