ISL6211

FN9043 Rev 1.00

Page 8 of 16

Nov 2001

Alternative Voltage Programming Input

Alternatively to VID code programming, the output voltage can

be set by an ALTV pin. The necessity of such input is dictated

by the fact that during power-up and some power saving

modes of operation, the voltage on the processor is insufficient

to provide correct VID codes to the controller. The required

core voltage should be set by some means external to the

processor. One of the most common approaches to this

problem is to provide hard wired VID code via multiplexer

controlled by the CPU. Providing high degree of flexibility, the

approach lacks simplicity and takes many external

components and valuable motherboard area. The ISL6211

uses the simpler way to set the core voltages when the CPU is

incapable of doing that.

The resistor-MOSFET network is connected to the ALTV pin as

it is shown on Simplified Power Diagram and in the Figure 2.

The calibrated current source of 10

A from ALTV pin creates

the voltage drop on the resistor when the MOSFET conducts

being activated by the input logic signal, for example DSX. The

controller regulates the output voltage to the level established

on the ALTV pin when this voltage is lower than the highest

VID programmed voltage (1.75V). When the MOSFET in

series with the resistor is turned off by the gate signal, the

ALTV pin voltage rises to VCC signaling the chip that DSX

signal is de-asserted. This high level signal commands the

controller to regulate the output voltage to the level

programmed by the VID code. This programming technique

relies on the tolerance of the internal pull-up current and

provides +/-5% accuracy of the voltage set.

If a better accuracy is required, the circuit shown in the Figure

3 can be used instead. With this approach the set point

accuracy depends mainly on the tolerance of an external

reference voltage source.

Output Voltage Droop

TABLE 1.

PIN NAME

NOMINAL

OUT1

VOLTAGE

VID4

VID3

VID2

VID1

VID0

00

00

0

1.750

00

00

1

1.700

00

01

0

1.650

00

01

1

1.600

00

10

0

1.550

00

10

1

1.500

00

11

0

1.450

00

11

1

1.400

01

00

0

1.350

01

00

1

1.300

01

01

0

1.250

01

01

1

1.200

01

10

0

1.150

01

10

1

1.100

01

11

0

1.050

01

11

1

1.000

10

00

0

0.975

10

00

1

0.950

10

01

0

0.925

10

01

1

0.900

10

10

0

0.875

10

10

1

0.850

10

11

0

0.825

10

11

1

0.800

11

00

0

0.775

11

00

1

0.750

11

01

0

0.725

11

01

1

0.700

11

10

0

0.675

11

10

1

0.650

11

11

0

0.625

11

11

1

0.600

NOTE: 0 = connected to GND or VSS, 1 = open or connected to Vcc

or voltage source of 2.5V...5.0 through pull-up resistors.

FIGURE 2. CIRCUIT FOR MORE PRECISE PROGRAMMING

OF START AND DSX VOLTAGES

R2

R1

DSX

ALTV

Q2

Q1

START

ISL6211

10

A

6

FIGURE 3. CIRCUIT FOR MORE PRECISE PROGRAMMING

OF START AND DSX VOLTAGES

R3

R2

DSX

6

ALTV

Q2

Q1

START

ISL6211

R1

VREF

R2

VSTART R1



VREF VSTART

–

R1 10

A



+

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

=

R3

VDSX R1



VREF VDSX

–

R1 10

A



+

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

=