2-218

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 PWM 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 (typically) 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. All

VID pin combinations resulting in an INHIBIT disable the IC

and the open-collector at the PGOOD pin.

Application Guidelines

Soft-Start Interval

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

output of the PWM converter. 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. Both linear outputs follow

a similar start-up sequence. 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

The PWM output does not switch until the soft-start voltage

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 three regulators.

The VID codes resulting in an INHIBIT as shown in Table 1

also shuts down the IC.

Layout Considerations

MOSFETs switch very fast and efficiently. The speed with

which the current transitions from one device to another

causes voltage spikes across the interconnecting

impedances and parasitic circuit elements. The voltage

spikes can degrade efficiency, radiate noise into the circuit,

and lead to device over-voltage stress. Careful component

UGATE

OCSET

PHASE

OVER-

CURRENT1

+

-

GATE

CONTROL

VCC

OC1

200

µA

+

+

FIGURE 9. OVER-CURRENT DETECTION

PWM

DRIVE

HIP6017

VCC

LGATE

PGND

PIN NAME

NOMINAL

OUT1

VOLTAGE

DACOUT

VID4

VID3

VID2

VID1

VID0

0

1

X

X

X

INHIBIT

0011

X

INHIBIT

00101

1.80

00100

1.85

00011

1.90

00010

1.95

00001

2.00

00000

2.05

11111

INHIBIT

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

through pull-up resistors, X = don’t care

HIP6017