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12 V

C

330 F

O

m

C

1000 F

I

m

GND

GND

3.3 V

R

2k

0.1 W, 1 %

SET

W

PTH12020W

7

10

4

5

6

2

3

9

Track

V

I

V

O

GND

Inhibit

1

Up Dn

Adjust

8

Sense

t − Time − 5 ms/div

OVERCURRENT PROTECTION

PTH12010W, PTH12010L

SLTS205E–JUNE 2003–REVISED APRIL 2006

Figure 12. Power-Up Application Circuit

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 13. Power-Up Waveforms

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

8 ms-15 ms) before allowing the output voltage to rise. The output then progressively rises to the module’s

(PTH12020W), operating from a 12-V input bus and configured for a 3.3-V output. The waveforms were

measured with a 5-A resistive load and the Auto-Track feature 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

25 ms.

For protection against load faults, all modules incorporate output overcurrent protection. Applying a load that

exceeds the regulator’s overcurrent threshold causes the regulated output to shut down. Following shutdown a

module periodically attempts 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.

15

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