UCC2585

UCC3585

PRELIMINARY

DESCRIPTION

The UCC2585/UCC3585 synchronous Buck controller provides flexible

high efficiency power conversion for output voltages as low as 1.25V with

guaranteed

±1% DC accuracy. Output currents are only limited by the

choice of external logic level MOSFETs. With an input voltage range of

2.5V to 6.0V it is the ideal choice for 3.3V only, battery input, or other low

voltage systems. Applications include local microprocessor core voltage

power supplies for desktop and Notebook computers, and high speed GTL

bus regulation. Its fixed frequency oscillator is capable of providing practical

PWM operation to 700kHz.

With its low voltage capability and inherent “always on” operation, the

UCC2585/UCC3585 causes VOUT to track VIN once VIN has exceeded

the threshold voltage of the external P channel MOSFET. Tracking can be

tailored for any application with a single resistor or disabled by connecting

TRACK to VIN. For dual supply rail microprocessors this feature negates

the need for external diodes to insure supply voltage tracking between the

+3.3V and lower voltage microprocessor core supplies.

(continued)

Low Voltage Synchronous Buck Controller

FEATURES

• Resistor Programmable 1.25V to 4.5V

• 2.5V to 6V Input Supply Range

• 1% DC Accuracy

• High Efficiency Synchronous

Switching

• Drives P-channel (High Side) and

N-channel (Low Side) MOSFETs

• Lossless Programmable Current Limit

• Logic Compatible Shutdown

• Programmable Frequency

• Start-up Voltage Tracking Protects

Dual Rail Microprocessors

07/99

12

14

6

11

8

PDRV

CLSET

ISENSE

13

5

9

NDRV

PWRGND

TRACK

N/C

1

4

10

2

15

VIN

VFB

ENB

COMP

SD

16

7

3

SS

GND

CT

ISET

C8

0.47

µF

Q1

IRF7404

Q2

IRF7401

L1 4.7

µF

C9

220

µF

C10

220

µF

C11

VOUT

RTN

RTN

VIN

220

µF

+

+

+

R4

100k

R2

549k

R6

3

R5

3

R1

10k

R3

27.4k

R12

32k

R10

36k

R11

82k

C6

470pF

C5

0.22

µF

C4

3.2N

C7

147pF

C1

150

µF

C2

150

µF

++

TYPICAL APPLICATION DIAGRAM

UDG-98024