Datasheet

STSEL A_VOUT

(Optional)

LMZ34002

SNVS989A –JULY 2013–REVISED SEPT 2013

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Slow-Start Circuit (SS)

Connecting the STSEL pin (Pin 29) to A_VOUT while leaving SS pin (Pin 28) open, enables the internal SS

capacitor with a slow-start interval of approximately 10 ms. Adding additional capacitance between the SS pin

and A_VOUT increases the slow-start time. Figure 45 shows an additional SS capacitor connected to the SS pin

and the STSEL pin connected to A_VOUT. See Table 6 below for SS capacitor values and timing interval.

Figure 45. Slow-Start Capacitor (C

) and STSEL Connection

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

(nF) open 10 15 22

SS Time (ms) 10 15 17 20

Inrush Current

During turn-on, as the LMZ34002 performs a slow-start sequence, an inrush current is induced as the output

capacitors charge up. The inrush current is in addition to the DC input current. The amount of inrush current

depends on the input voltage, output voltage and amount of output capacitance. Table 7 shows the typical inrush

current for the input voltage, output voltage and the amount of output capacitance. Increasing the slow-start

capacitor reduces the inrush current by slowing down the ramp of the output voltage. See Slow-Start Circuit (SS).

Table 7. Typical Inrush Current

Output Capacitance → 100 µF ceramic 200 µF

(1)

320 µF

(1)

430 µF

(1)

VIN (V) VOUT (V) Inrush Current (A)

–3.3 0.1 0.1 0.1 0.1

–5 0.1 0.2 0.2 0.3

–12 0.3 0.8 1.2 1.8

–15 0.4 1.3 2.5 3.6

–3.3 0.1 0.1 0.1 0.1

–5 0.1 0.1 0.1 0.2

–12 0.2 0.4 0.6 0.8

–15 0.3 0.5 0.9 1.3

–3.3 0.1 0.1 0.1 0.1

–5 0.1 0.1 0.2 0.2

–12 0.2 0.2 0.3 0.5

–15 0.3 0.3 0.5 0.7

–3.3 0.2 0.2 0.2 0.2

36 –5 0.2 0.2 0.2 0.2

–12 0.2 0.3 0.4 0.4

(1) This amount of capacitance includes the required 100 µF of ceramic capacitance with additional bulk capacitance.

Product Folder Links: LMZ34002