www.ti.com

Soft-Start Power Up

5 V

CIN

1,000

µF

COUT

330

µF

GND

GND

3.3 V

PTH05020W

7

10

4

5

6

2

3

9

Track

VIN

VO

GND

Inhibit

1

Up

Dn

Adjust

Sense

0.1 W, 1%

8

Vin (1 V/Div)

Vout (1 V/Div)

Iin (5 A/Div)

5 ms/div

Over-Current Protection

PTH05050W

SLTS213D – MAY 2003 – REVISED JUNE 2007

The Auto-Track feature allows the power-up of multiple modules to be directly controlled from the Track pin.

However in a stand-alone configuration, or when the Auto-Track feature is not being used, the Track pin should

Figure 6.

When the Track pin is connected to the input voltage the Auto-Track function is permanently disengaged. This

allows the module to power up entirely under the control of its internal soft-start circuitry. When power up is

under soft-start control, the output voltage rises to the set-point at a quicker and more linear rate.

Figure 7.

From the moment a valid input voltage is applied, the soft-start control introduces a short time delay (typically

5ms-10ms) before allowing the output voltage to rise. The output then progressively rises to the module’s

setpoint voltage. Figure 7 shows the soft-start power-up characteristic of the 22-A output product (PTH05020W),

operating from a 5-V input bus and configured for a 3.3-V output. The waveforms were measured with a 5-A

resistive load, with Auto-Track disabled. The initial rise in input current when the input voltage first starts to rise

is the charge current drawn by the input capacitors. Power-up is complete within 15 ms.

For protection against load faults, all modules incorporate output over-current protection. Applying a load that

exceeds the regulator's over-current threshold will cause the regulated output to shut down. Following shutdown

a module will periodically attempt to recover by initiating a soft-start power-up. This is described as a hiccup

mode of operation, whereby the module continues in a cycle of successive shutdown and power up until the

load fault is removed. During this period, the average current flowing into the fault is significantly reduced. Once

the fault is removed, the module automatically recovers and returns to normal operation.

11

Submit Documentation Feedback