SLVS839F July 2008 – October 2014 TPS54331
The TPS54331 device implements current mode control that uses the COMP pin voltage to turn off the high-side MOSFET on a cycle-by-cycle basis. During each cycle the switch current and the COMP pin voltage are compared. When the peak inductor current intersects the COMP pin voltage, the high-side switch is turned off. During overcurrent conditions that pull the output voltage low, the error amplifier responds by driving the COMP pin high, causing the switch current to increase. The COMP pin has a maximum clamp internally, which limit the output current.
The TPS54331 device provides robust protection during short circuits. Overcurrent runaway is possible in the output inductor during a short circuit at the output. The TPS54331 device solves this issue by increasing the off time during short-circuit conditions by lowering the switching frequency. The switching frequency is divided by 1, 2, 4, and 8 as the voltage ramps from 0 to 0.8 V on VSENSE pin. The relationship between the switching frequency and the VSENSE pin voltage is listed in Table 2.
|SWITCHING FREQUENCY||VSENSE PIN VOLTAGE|
|570 kHz||VSENSE ≥ 0.6 V|
|570 kHz / 2||0.6 V > VSENSE ≥ 0.4 V|
|570 kHz / 4||0.4 V > VSENSE ≥ 0.2 V|
|570 kHz / 8||0.2 V > VSENSE|