Datasheet

SS/TR

STSELAGND

(Optional)

LMZ31503

SNVS992 –JULY 2013

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Slow Start (SS/TR)

Connecting the STSEL pin to AGND and leaving SS/TR pin open enables the internal SS capacitor with a slow

start interval of approximately 1.1 ms. Adding additional capacitance between the SS pin and AGND increases

the slow start time. Table 6 shows an additional SS capacitor connected to the SS/TR pin and the STSEL pin

connected to AGND. See Table 6 below for SS capacitor values and timing interval.

Figure 32. Slow-Start Capacitor (C

) and STSEL Connection

Table 6. Slow-Start Capacitor Values and Slow-Start Time

(pF) open 2200 4700 10000 15000 22000 25000

SS Time (msec) 1.1 1.9 2.8 4.6 6.4 8.8 9.8

Overcurrent Protection

For protection against load faults, the LMZ31503 incorpoates output overcurrent protection. Applying a load that

exceeds the regulator's overcurrent threshold causes the regulated output to shut down. Following shutdown, the

output voltage 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, as shown in Figure 33. 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, as shown in Figure 34.

Figure 33. Overcurrent - Hiccup Mode Figure 34. Removal of Overcurrent Condition

Product Folder Links: LMZ31503