10

back through the lower MOSFETs, avoiding a possibly

destructive ringing of the capacitors and output inductors. If

the conditions that caused the over-voltage still persist, the

clamped to ground, as a hysteretic shunt regulator.

Under-Voltage

The VSEN pin also detects when the CORE voltage falls more

than 10% below the VID programmed level. This causes

PGOOD to go low, but has no other effect on operation and is

not latched. There is also hysteresis in this detection point.

Over-Current

In the event of an over-current condition, the over-current

protection circuit reduces the average current delivered to

less than 25% of the current limit. When an over-current

condition is detected, the controller forces all PWM outputs

into a three state mode. This condition results in the gate

driver removing drive to the output stages.The HIP6311A

goes into a wait delay timing cycle that is equal to the Soft-

Start ramp time. PGOOD also goes “low” during this time

due to VSEN going below its threshold voltage.To lower the

average output dissipation, the Soft-Start initial wait time is

increased from 32 to 2048 cycles, then the Soft-Start ramp is

initiated. At a PWM frequency of 200kHz, for instance, an

over-current detection would cause a dead time of 10.24ms,

then a ramp of 10.08ms.

At the end of the delay, PWM outputs are restarted and the

Soft-Start ramp is initiated. If a short is present at that time,

the cycle is repeated. This is the hiccup mode.

Figure 6 shows the supply shorted under operation and the

hiccup operating mode described above. Note that due to

the high short circuit current, over-current is detected before

completion of the start-up sequence so the delay is not quite

as long as the normal Soft-Start cycle.

CORE Voltage Programming

The voltage identification pins (VID0, VID1, VID3, and VID4)

by an internal 20

µA current source and accepts open-

collector/open-drain/open-switch-to-ground or standard low-

voltage TTL or CMOS signals.

Table 1 shows the nominal DAC voltage as a function of the

VID codes. The power supply system is

±0.5% accurate over

the operating temperature and voltage range.

PGOOD

SHORT

50A/Div

CURRENT

ATX SUPPLY ACTIVATED BY ATX “PS-ON PIN”

HICCUP MODE. SUPPLY POWERED BY ATX SUPPLY

CORE LOAD CURRENT = 31A, 5V LOAD = 5A

SHORT APPLIED HERE

FIGURE 6. SHORT APPLIED TO SUPPLY AFTER POWER-UP

TABLE 1. VOLTAGE IDENTIFICATION CODES

VID4

VID3

VID2

VID1

VID0

VDAC

111

11

Off

111

10

1.100

111

01

1.125

111

00

1.150

110

11

1.175

110

10

1.200

110

01

1.225

110

00

1.250

101

11

1.275

101

10

1.300

101

01

1.325

101

00

1.350

100

11

1.375

100

10

1.400

100

01

1.425

100

00

1.450

011

11

1.475

011

10

1.500

011

01

1.525

011

00

1.550

010

11

1.575

010

10

1.600

010

01

1.625

010

00

1.650

001

11

1.675

001

10

1.700

001

01

1.725

001

00

1.750

000

11

1.775

000

10

1.800

000

01

1.825

000

00

1.850

HIP6311A

HIP6311A