JAJSPC8C December 2022 – February 2024 TPSM33615 , TPSM33625
PRODUCTION DATA
The TPSM336x5 is protected from overcurrent conditions by using cycle-by-cycle current limiting circuitry on both the high-side (HS) and low-side (LS) MOSFETs. The current is compared every switching cycle to the current limit threshold. During an overcurrent condition, the output voltage decreases with reduced switching frequency.
High-side MOSFET overcurrent protection is implemented by the typical peak-current mode control scheme. The HS switch current is sensed when the HS is turned on after a short blanking time. The HS switch current is compared to the minimum of a fixed current set point or the output of the internal error amplifier loop minus the slope compensation every switching cycle. Because the output of the internal error amplifier loop has a maximum value and slope compensation increases with duty cycle, HS current limit decreases with increased duty factor if duty cycle is above 35%.
When the LS switch is turned on, the current going through it is also sensed and monitored. Like the high-side device, the low-side device has a turn-off commanded by the internal error amplifier loop. In the case of the low-side device, turn-off is prevented if the current exceeds this value, even if the oscillator normally starts a new switching cycle. Also like the high-side device, there is a limit on how high the turn-off current is allowed to be. This is called the low-side current limit. If the LS current limit is exceeded, the LS MOSFET stays on and the HS switch is not to be turned on. The LS switch is turned off after the LS current falls below this limit and the HS switch is turned on again as long as at least one clock period has passed since the last time the HS device has turned on.
If, during current limit, the voltage on the FB input falls below about 0.4 V (VHICCUP) due to a short circuit, the device enters hiccup mode. In this mode, the device stops switching for tW or about 50 ms, and then goes through a normal re-start with soft start. If the short-circuit condition remains, the device runs in current limit for about 5 ms (typical) and then shuts down again. This cycle repeats as long as the short-circuit condition persists.