JAJSFL9C July 2016 – June 2018 TPS546C20A
PRODUCTION DATA.
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To control the inrush current required to charge the output capacitor bank during start up, the devices implement a soft-start time. When the device is enabled, the feedback reference voltage, VREF, ramps from 0 V to the final level defined by Equation 3 at a slew rate defined by the TON_RISE command. The specified rise times are defined by the slew rate required to ramp the reference voltage from 0 V to the final value at each given rise time.
The actual rise time of the converter output is slightly less than the rise time defined by the TON_RISE command. This difference occurs because switching does not occur until the error-amplifier output reaches the valley of the PWM ramp. During the soft-start time, the error-amplifier output voltage starts at 0 V and then begins switching again only when the VSHARE voltage reaches the valley of the PWM ramp which is 1.23 V (typical). When the VSHARE voltage reaches the valley of the PWM ramp, the converter output voltage rises quickly until the feedback voltage, VFB, reaches the VREF level, at which point they track through the end of the soft-start period.
The devices support several soft-start times from 1 ms to 100 ms which are selected by the TON_RISE command.
The value of TON_RISE comman can be set through the PMBus interface or alternatively by the resistor connected from the SS pin to AGND.
Table 3 lists the E48 series resistors with no worse than 1% tolerance suggested for the TON_RISE setting. Issuing a TON_RISE command after start-up overwrites the TON_RISE value set by the external resistor. If the device restarts after losing power completely, the TON_RISE value set by external resistor overwrites any value stored from previous the TON_RISE operation.
TON_RISE (ms) | RESISTOR VALUE (kΩ) |
---|---|
3 | Short to AGND |
1 | 7.15 |
2 | 14 |
3 | 22.6 |
5 | 34.8 |
7 | 51.1 |
10 | 78.7 |
27 | 121 |
52 | 187 |
3TON_RISE = EEPROM | SS pin pulled up to BP3 |
TON_RISE = 3 ms, declare fault (sets STATUS_MFR_SPEC[3] (iv_ppv0) in the STATUS_MFR_SPECIFIC (80h) command), no SMBALERT | Nonconverge (cannot resolve 4 consecutive TON_RISE commans) |