ZHCSIE3B June 2018 – May 2019 LMZM33606
PRODUCTION DATA.
The soft-start and tracking features control the output voltage ramp during start-up. The soft-start feature reduces inrush current during start-up and improves system performance and reliability. If the SS/TRK pin is floating, the LMZM33606 starts up following the fixed, 5-ms internal soft-start ramp. Use CSS to extend soft-start time when there are a large amount of output capacitors, or the output voltage is high, or the output is heavily loaded during start-up.
If longer soft-start time is desired, an external capacitor can be added from SS/TRK pin to AGND. There is a 2 µA (typical) internal current source, ISSC, to charge the external capacitor. For a desired soft-start time tSS, capacitance of CSS can be found by Equation 6.
where
LMZM33606 can track an external voltage ramp applied to the SS/TRK pin, if the ramp is slower than the internal soft-start ramp. The external ramp final voltage after start-up must be greater than 1.5 V to avoid noise interfering with the reference voltage. Figure 40 shows how to use resistor divider to set VOUT to follow an external ramp.