7.3.6 Output Discharge Control

TPS54526 discharges the output when EN is low, or the controller is turned off by the protection functions (OVP,

UVP, UVLO and thermal shutdown). The output is discharged by an internal 50-Ω MOSFET which is connected

from VO to PGND. The internal low-side MOSFET is not turned on during the output discharge operation to

avoid the possibility of causing negative voltage at the output.

7.3.7 Current Protection

The output overcurrent protection (OCP) is implemented using a cycle-by-cycle valley detect control circuit.

The switch current is monitored by measuring the low-side FET switch voltage between the SW pin and GND.

This voltage is proportional to the switch current. To improve accuracy, the voltage sensing is temperature

compensated.

During the on-time of the high-side FET switch, the switch current increases at a linear rate determined by VIN,

VOUT, the on-time, and the output inductor value. During the on-time of the low-side FET switch, this current

decreases linearly. The average value of the switch current is the load current IOUT. If the measured voltage is

above the voltage proportional to the current limit. Then, the device constantly monitors the low-side FET switch

voltage, which is proportional to the switch current, during the low-side on-time.

The converter maintains the low-side switch on until the measured voltage is below the voltage corresponding to

the current limit at which time the switching cycle is terminated and a new switching cycle begins. In subsequent

switching cycles, the on-time is set to a fixed value and the current is monitored in the same manner.

There are some important considerations for this type of overcurrent protection. The load current one half of

the peak-to-peak inductor current higher than the overcurrent threshold. Also when the current is being limited,

the output voltage tends to fall as the demanded load current may be higher than the current available from

the converter. This may cause the output under-voltage protection circuit to be activated. When the overcurrent

condition is removed, the output voltage will return to the regulated value. This protection is non-latching.

7.3.8 Over/Under Voltage Protection

TPS54526 monitors a resistor divided feedback voltage to detect over and under voltage. When the feedback

voltage becomes higher than 125% of the target voltage, the OVP comparator output goes high and the circuit

latches as both the high-side and low-side MOSFET drivers turns off. When the feedback voltage becomes

lower than 65% of the target voltage, the UVP comparator output goes high and an internal UVP delay counter

begins. After 250 μs, the device latches off both internal top and bottom MOSFET. This function is enabled

approximately 1.7 x softstart time.

7.3.9 UVLO Protection

Undervoltage lock out protection (UVLO) monitors the voltage of the VREG5 pin. When the VREG5 voltage is lower

than UVLO threshold voltage, the TPS54526 is shut off. This is protection is non-latching.

7.3.10 Thermal Shutdown

TPS54526 monitors the temperature of itself. If the temperature exceeds the threshold value (typically 165°C),

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

TPS54526

SLVSB84D – MAY 2012 – REVISED APRIL 2021

www.ti.com

10

Submit Document Feedback

Copyright © 2021 Texas Instruments Incorporated

Product Folder Links: TPS54526