HIP6503

FN4882 Rev 5.00

Page 8 of 14

July 21, 2005

Not shown in these diagrams is the deglitching feature used

to protect against false sleep state tripping. Both S3 and S5

pins are protected against noise by a 2

s filter (typically 1 -

4

s). This feature is useful in noisy computer environments if

the control signals have to travel over significant distances.

Additionally, the S3 pin features a 200

s delay in

transitioning to sleep states. Once the S3 pin goes low, an

internal timer is activated. At the end of the 200

s interval, if

the S5 pin is low, the HIP6503 switches into S5 sleep state; if

the S5 pin is high, the HIP6503 goes into S3 sleep state.

Soft-Start Circuit

SOFT-START INTO SLEEP STATES (S3, S4/S5)

The 5VSB POR function initiates the soft-start sequence. An

internal 10

A current source charges an external capacitor.

The error amplifiers reference inputs are clamped to a level

proportional to the SS (soft-start) pin voltage. As the SS pin

voltage slews from about 1.25V to 2.5V, the input clamp

allows a rapid and controlled output voltage rise.

Figure 7 shows the soft-start sequence for the typical

application start-up in sleep state with all output voltages

enabled. At time T0 5VSB (bias) is applied to the circuit. At

time T1 the 5VSB surpasses POR level. An internal fast

charge circuit quickly raises the SS capacitor voltage to

approximately 1V, then the 10

A current source continues

the charging. The soft-start capacitor voltage reaches

approximately 1.25V at time T2, at which point the

inputs start their transition, resulting in the output voltages

ramping up proportionally. The ramp-up continues until time

T3 when the two voltages reach the set value. As the soft-

start capacitor voltage reaches approximately 2.75V, the

under-voltage monitoring circuit of this output is activated

and the soft-start capacitor is quickly discharged to

approximately 1.25V. Following the 3ms (typical) time-out

between T3 and T4, the MSEL and EN5VDL selections are

latched in, and the soft-start capacitor commences a second

ramp-up designed to smoothly bring up the remainder of the

voltages required by the system. At time T5 all voltages are

within regulation limits, and as the SS voltage reaches

2.75V, all the remaining UV monitors are activated and the

SS capacitor is quickly discharged to 1.25V, where it

only active while in an active state, it does not come up, but

5VSB

3.3V,

S3

S5

5VDLSB

DLA

3V3DLSB

3V3DL

5VDL

5V, 12V

5VSB

3.3V,

S3

S5

DRV2

VSEN 2

VSEN2

INTERNAL

DEVICES

VCLK

DLA

VSEN1

5V, 12V

FIGURE 7. SOFT-START INTERVAL IN A SLEEP STATE

(ALL OUTPUTS ENABLED)

0V

0V

TIME

SOFT-START

(1V/DIV)

OUTPUT

(1V/DIV)

VOLTAGES

T1 T2

T3

T0

5VSB

(1V/DIV)

T5

T4