HIP6501A

FN4749 Rev 6.00

Page 9 of 14

December 30, 2004

Soft-Start into Active States (S0, S1)

If both S3 and S5 are logic high at the time the 5VSB is

applied, the HIP6501A will assume an active state and keep

off the controlled external transistors until about 50ms after

the ATX’s 12V output (sensed at the 12V pin) exceeds the

set threshold (typically 10.8V). This timeout feature is

necessary in order to ensure the main ATX outputs are

stabilized. The timeout also assures smooth transitions from

sleep into active when sleep states are being supported.

During sleep to active state transitions from conditions

where the outputs are initially 0V (such as S4/S5 to S0

transition with EN3VDL = 1 and EN5VDL = 0, or simple

pulled high through the body diodes of the N-channel

MOSFETs connected between these outputs and the 3.3V

and 5V ATX outputs, respectively. Figure 10 shows this start-

up scenario.

turned on at time T0. Similarly, the soft-start capacitor has

already been charged up to 1.25V and the clamp is active,

awaiting for the 12V POR timer to expire. As a result of

output capacitors charge up through the body diodes of Q3

and Q5, respectively (see Figure 3). At time T1, the 12V ATX

output exceeds the HIP6501A’s 12V under-voltage

threshold, and the internal 50ms (typical) timer is initiated. At

T2 the time-out initiates a soft-start, and the memory output

is ramped-up, reaching regulation limits at time T3.

Simultaneous with the memory voltage ramp-up, the DLA

pin is pulled high (to 12V), turning on Q3 and Q5, and

time T2. At time T4, when the soft-start voltage reaches

approximately 2.8V, the under-voltage monitoring circuits are

enabled and the soft-start capacitor is quickly discharged to

approximately 2.45V.

Requests to go into a sleep state during an active state soft-

start ramp-up result in a chip reset, followed by a new soft-

start sequence into the desired state.

Fault Protection

All the outputs are monitored against under-voltage events.

A severe over-current caused by a failed load on any of the

outputs, would, in turn, cause that specific output to

suddenly drop. If any of the output voltages drop below 69%

of their set value, such event is reported by having the

FAULT/MSEL pin pulled to 5V. Additionally, the 2.5/3.3V

memory regulator is internally current limited while in a sleep

state. Exceeding the maximum current rating of this output in

a sleep state can lead to output voltage drooping. If

excessive, this droop can ultimately trip the under-voltage

detector and send a FAULT signal to the computer system.

However, a FAULT condition will only set off the FAULT flag,

and it will not shut off or latch off any part of the circuit. If

shutdown or latch off of the circuit is desired, this can be

achieved by externally pulling or latching the SS pin low.

Pulling the SS pin low will also force the FAULT pin to go low.

Under-voltage sensing is disabled on all disabled outputs

and during soft-start ramp-up intervals. SS voltage reaching

the 2.8V threshold signals activation of the under-voltage

monitor.

Another condition that could set off the FAULT flag is chip

over-temperature. If the HIP6501A reaches an internal

(FAULT/MSEL pulled high), but the chip continues to operate

unconditional latched shutdown of all outputs takes place.

and then on.

Output Voltages

The output voltages are internally set and do not require any

external components. Selection of the memory voltage is

done by means of an external resistor connected between

the FAULT/MSEL pin and ground. An internal 40

A (typical)

current source creates a voltage drop across this resistor.

During every 5VSB trip above POR level, this voltage is

compared with an internal reference (200mV typically).

Based on this comparison, the output voltage is set at either

important that no capacitor is connected to the FAULT/MSEL

pin; the presence of a capacitive element at this pin can lead

to false memory voltage selection. See Figure 11 for details.

FIGURE 10. SOFT-START INTERVAL IN AN ACTIVE STATE

0V

0V

TIME

SOFT-START

(1V/DIV)

OUTPUT

(1V/DIV)

VOLTAGES

T1

T2

T0

INPUT VOLTAGES

(2V/DIV)

T4

T3

DLA PIN

+5VSB

(2V/DIV)