2-289

MOSFET switching. The over-current function will trip at a peak

The OC trip point varies with MOSFET’s rDS(ON)

temperature variations. To avoid over-current tripping in the

normal operating load range, determine the ROCSET

resistor value from the equation above with:

where

∆I is the output inductor ripple current.

For an equation for the ripple current see the section under

component guidelines titled ‘Output Inductor Selection’.

OUT1 Voltage Program

The output voltage of the PWM1 converter is programmed to

(OUT1) is designed to supply the core voltage of Intel’s

advanced microprocessors. The voltage identification (VID)

pins program an internal voltage reference (DACOUT) with a

TTL-compatible 5-bit digital-to-analog converter (DAC). The

level of DACOUT also sets the PGOOD and OVP thresholds.

Table 1 specifies the DACOUT voltage for the different

combinations of connections on the VID pins. The VID pins

can be left open for a logic 1 input, because they are internally

pulled up to an internal voltage of about 5V by a 10

µA current

source. Changing the VID inputs during operation is not

recommended and could toggle the PGOOD signal and

exercise the over-voltage protection. ‘11111’ VID pin

combination disables the IC and opens the PGOOD pin.

OUT2 Voltage Selection

The AGP regulator output voltage is internally set to one of

two discrete levels, based on the status of the SELECT pin.

SELECT pin is internally pulled ‘high’, such that left open,

the AGP output voltage is by default set to 3.3V. The other

discrete setting available is 1.5V, which can be obtained by

grounding the SELECT pin using a jumper or another

suitable method capable of sinking a few tens of

microamperes. The status of the SELECT pin cannot be

changed during operation of the IC without immediately

causing a fault condition.

Application Guidelines

Soft-Start Interval

Initially, the soft-start function clamps the error amplifier’s output

of the PWM converters. This generates PHASE pulses of

increasing width that charge the output capacitor(s). After the

output voltage increases to approximately 70% of the set value,

the reference input of the error amplifier is clamped to a voltage

proportional to the SS pin voltage. The resulting output voltages

start-up as shown in Figure 6.

The soft-start function controls the output voltage rate of rise

to limit the current surge at start-up. The soft-start interval

and the surge current are programmed by the soft-start

I

I

OCSET

R

OCSET

×

r

DS ON

()

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

TABLE 1. OUT1 VOLTAGE PROGRAM

PIN NAME

NOMINAL

DACOUT

VOLTAGE

VID4

VID3

VID2

VID1

VID0

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

0

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

10100

3.1

10011

3.2

10010

3.3

10001

3.4

10000

3.5

NOTE: 0 = connected to GND, 1 = open or connected to 5V through

pull-up resistors

HIP6020