Datasheet

SS/TR

STSELAGND

(Optional)

LMZ31707

SLVSBV7A –JUNE 2013–REVISED AUGUST 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 1.2 ms. Adding additional capacitance between the SS pin and AGND increases

the slow start time. Increasing the slow start time will reduce inrush current seen by the input source and reduce

the current seen by the device when charging the output capacitors. To avoid the activation of current limit and

ensure proper start-up, the SS capacitor may need to be increased when operating near the maximum output

capacitance limit.

Figure 30 shows an additional SS capacitor connected to the SS/TR pin and the STSEL pin connected to AGND.

See Table 8 below for SS capacitor values and timing interval.

Figure 30. Slow-Start Capacitor (C

) and STSEL Connection

Table 8. Slow-Start Capacitor Values and Slow-Start Time

(nF) open 3.3 4.7 10 15 22 33

SS Time (msec) 1.2 2.1 2.5 3.8 5.1 7.0 9.8

Overcurrent Protection

For protection against load faults, the LMZ31707 incorporates output overcurrent protection. The overcurrent

protection mode can be selected using the OCP_SEL pin. Leaving the OCP_SEL pin open selects hiccup mode

and connecting it to AGND selects cycle-by-cycle mode. In hiccup mode, applying a load that exceeds the

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

periodically attempts to recover by initiating a soft-start power-up as shown in Figure 31. 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

which reduces power dissipation. Once the fault is removed, the module automatically recovers and returns to

normal operation as shown in Figure 32.

In cycle-by-cycle mode, applying a load that exceeds the regulator's overcurrent threshold limits the output

current and reduces the output voltage as shown in Figure 33. During this period, the current flowing into the

fault remains high causing the power dissipation to stay high as well. Once the overcurrent condition is removed,

the output voltage returns to the set-point voltage as shown in Figure 34.

Product Folder Links: LMZ31707