9

FN4587.1

April 13, 2005

current trip levels for each PWM converter. As shown in

Figure 9, the internal 200

µA current sink develops a voltage

signal enables the over-current comparator (OVER-

CURRENT1 or OVER-CURRENT2). When the voltage

current comparator trips to set the over-current latch. Both

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

The OC trip point varies with MOSFET’s temperature. To avoid

over-current tripping in the normal operating load range,

where

∆I is the output inductor ripple current.

For an equation for the output inductor 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

designed to supply the microprocessor core voltage. The

voltage identification (VID) pins program an internal voltage

reference (DACOUT) through a TTL-compatible 5-bit digital-to-

analog converter. 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 +5V by a 10

µA current source. Changing

the VID inputs during operation is not recommended. The

sudden change in the resulting reference voltage could toggle

the PGOOD signal and exercise the over-voltage protection.

The ‘11111’ VID pin combination resulting in an INHIBIT

disables the IC and the open-collector at the PGOOD pin.

Application Guidelines

Soft-Start Interval

Initially, the soft-start function clamps the error amplifiers’

output of the PWM converters. After the output voltage

increases to approximately 80% 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

voltage sequence is 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 is

a faster soft-start interval increases the peak surge current.

The peak surge current occurs during the initial output

voltage rise to 80% of the set value.

Shutdown

Neither PWM output switches until the soft-start voltage

the reference on each linear’s amplifier is clamped to the

soft-start voltage. Holding the SS pin low (with an open drain

or collector signal) turns off all four regulators.

The ‘11111’ VID code resulting in an INHIBIT as shown in

Table 1 also shuts down the IC.

UGATE

OCSET

PHASE

OVER-

CURRENT2

+

-

GATE

CONTROL

VCC

OC2

200

µA

+

+

FIGURE 9. OVER-CURRENT DETECTION

PWM

DRIVE

HIP6019B

I

PEAK

=

I

OCSET

R

OCSET

×

r

DS ON

()

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

TABLE 1.

PIN NAME

NOMINAL

OUT1

VOLTAGE

DACOUT

VID4

VID3

VID2

VID1

VID0

01

11

1

1.30

01

11

0

1.35

01

10

1

1.40

01

10

0

1.45

01

01

1

1.50

01

01

0

1.55

01

00

1

1.60

01

00

0

1.65

00

11

1

1.70

00

11

0

1.75

00

10

1

1.80

00

10

0

1.85

00

01

1

1.90

00

01

0

1.95

00

00

1

2.00

00

00

0

2.05

11

11

1

INHIBIT

11

11

0

2.1

11

10

1

2.2

HIP6019B