There are some important considerations for this type of overcurrent protection. The load current is higher than

the overcurrent threshold by one half of the peak-to-peak inductor ripple current. Also, when the current is

limited, the output voltage tends to fall as the demanded load current can be higher than the current available

from the converter, which can cause the output voltage to fall. When the FB voltage falls below the UVP

threshold voltage, the UVP comparator detects the fall and the device shuts down after the UVP deglitch time

and restarts after the hiccup wait time.

When the overcurrent condition is removed, the output voltage returns to the regulated value.

The TPSM861253 is a FCCM mode part. In this mode, the device has negative inductor current at light loading.

The device has NOC (negative overcurrent) protection to avoid too large negative current. NOC protection

detects the valley of inductor current. When the valley value of inductor current exceeds the NOC threshold, the

IC turns off the low side then turns on the high side. When the NOC condition is removed, the device returns to

normal switching.

7.3.6 Undervoltage Lockout (UVLO) Protection

UVLO protection monitors the internal regulator voltage. When the voltage is lower than UVLO threshold voltage,

the device is shut off. This protection is a non-latch protection.

7.3.7 Thermal Shutdown

The device monitors the temperature of itself. If the temperature exceeds the threshold value, the device is shut

off. This protection is a non-latch protection.

7.4 Device Functional Modes

7.4.1 FCCM Mode Operation

The TPSM861253 operates in forced CCM (FCCM) mode, which keeps the converter operating in continuous

current mode during light load conditions and allows the inductor current to become negative. During FCCM

mode, the switching frequency is maintained at an almost constant level over the entire load range, which is

designed for applications requiring tight control of the switching frequency and output voltage ripple at the cost of

lower efficiency under light load.

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TPSM861253

SLUSFD2A – SEPTEMBER 2023 – REVISED JANUARY 2024

Copyright © 2024 Texas Instruments Incorporated

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