AT1621 - Aimtron Technology

AT1621

Single PWM and Triple Linear Power Controller

2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.

Tel: 886-3-563-0878 WWW: http://www.aimtron.com.tw

Fax: 886-3-563-0879 Email: service@aimtron.com.tw

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Features

˙Provides 4 Regulated Voltages

-CPU Core, AGP Bus, Memory, and GTL Bus

Power

˙Drives two N-channel MOSFETs

˙Linear Regulator Drives Compatible with both

MOSFET and Bipolar Series Pass Transistors

˙Operates from +5V and +12V input

˙Fixed or Externally Resistor-Adjustable Linear

Outputs

˙Simple Single-Loop Control

-Voltage-mode PWM control

˙Fast Transient Response

- High-bandwidth error amplifier

- Full 0% to 100% duty ratio

˙Excellent Output Voltage Regulation

-Core PWM Output: ±1% Over Temperature

-Other Outputs: ±3% Over Temperature

˙TTL-compatible 5 bit digital-to-analog output

voltage selection

- Wide range 1.3VDc to 3.5VDC

- 0.1V binary steps from 2.1VDC to 3.5VDC

- 0.05V binary steps from 1.3VDC to 2.05VDC

˙Power-Good Output Voltage Monitor

˙Over-Voltage and Over-Current Fault Monitors

-Does not require extra current sensing element

˙Small converter size

-Constant Frequency Operation

-200 kHz Free-Running Oscillator

Programmable From 50 kHz to Over 1 MHz

Applications

˙Motherboard Power Regulation for Computers

˙Low-Voltage Distributed Power Supplies

General Description

The AT1621 provides complete control and

protection for four voltages in high-performance,

graphics intensive computer applications. It

integrates a PWM controller and three linear

controllers into a 28-pin SOIC package. One PWM

controller regulates the CPU core voltage with a

synchronous-rectified buck topology. The linear

controllers regulate the computer system’s AGP

1.5V or 3.3V bus power, the 1.5V GTL bus power,

and the 1.8V power for the North/South Bridge core

voltage and/or cache memory circuits.

The AT1621 includes a fully-TTL compatible 5-bit

digital-to-analog converter (DAC) that adjusts the

output voltage from 2.1VDC to 3.5VDC in 0.1V

increments and from 1.3VDC to 2.1VDC in 0.05V

steps. The precision reference and voltage–mode

regulator hold the selected output voltage to within

±1% over temperature. The AGP bus power linear

controller’s output is user-selectable, through a

TTL-compatible signal applied at the SELECT pin,

for levels of 1.5V or 3.3V with ±3% accuracy.

Based on the status of the FIX pin, the other two

linear regulators provide either fixed output

voltages of 1.5V±3% and 1.8V±3%, or user-

adjustable by means of an external resistor divider.

All linear controllers can employ either N-channel

MOSFETs or bipolar NPNs for the pass transistor.

The AT1621 monitors all the output voltage. A

single is issued when the core is within ±10% of

the DAC setting and all other outputs are above

their under-voltage levels. Additional built-in over-

voltage protection for the core output uses the lower

MOSFET to prevent output voltage above 115% of

the DAC setting. The PWM controllers’ over-

current function monitors the output current by

using the rDS

(

)

of the upper MOSFET, which

eliminates the need for a current sensing resistor.