MB39A105
■SETTING THE SOFT-START TIMES
To prevent rush currents when the IC is turned on, you can set a soft-start by connecting soft-start capacitors (CSCP) to the CSCP terminal (pin 2). When IC starts (VCC ≥ UVLO threshold voltage), the external soft-start capacitors (CSCP) connected to CSCP terminal are charged at 11 ∝A. The error amplifier output (FB (pin 8) ) is determined by comparison between the lower one of the potentials at two non-inverted input terminals (0.5 V in an internal reference voltage, CSCP terminal voltages) and the inverted input terminal voltage (−INE (pin 1) voltage).
The FB terminal voltage is decided for the soft-start period by the comparison between 0.5 V in an internal reference voltage and the voltages of the CSCP terminal. The DC/DC converter output voltage rises in proportion to the CSCP terminal voltage as the soft-start capacitor connected to the CSCP terminal is charged.
The soft-start time is obtained from the following formula:
Soft-start time: ts (time to output 100%)
ts (s) =: 0.045 ⋅ CSCP (∝F)
CSCP terminal voltage
Error Amp block −INE voltage
Soft-start time (ts)
• Soft-Start Circuit
VO | |
| VREF |
| 11 ∝A |
R1 | |
−INE | |
1 | |
| L priority |
R2 | Error Amp |
| − |
2 | + |
CSCP | + |
| (0.5 V) |
CSCP | |
8 | |
FB | UVLO |
|