V

=

TRIP

(V-V )

IN

O

2

1

·

·

L

f

SW

V

O

¾

V

IN

I

-

OCL

(

)

R

(k )=

TRIP

W

V

(mV)

TRIP

I

( A)

TRIP

m

¾

TPS53125

SLVS947A – OCTOBER 2009 – REVISED OCTOBER 2009

www.ti.com

Output Discharge Control

TPS53125 discharges the outputs when ENx is low, or the controller is turned off by the protection functions

(OVP, UVP, UVLO, and thermal shutdown). The device discharges output using an internal 40-

Ω MOSFET which

is connected to VOx and PGNDx. The external low-side MOSFET is not turned on during the output discharge

operation to avoid the possibility of causing negative voltage at the output. This discharge ensures that on start

the regulated voltage always initializes from 0 V.

Over Current Limit

TPS53125 has cycle-by-cycle over current limit feature. The over current limits the inductor valley current by

inductor current is larger than the over current limit (OCL), the TPS53125 delays the start of the next switching

provide an accuracy and cost effective solution without external devices. To program the OCL, the TRIP pin

should be connected to GND through a trip voltage setting resistor, according to the following equations.

(1)

(2)

The trip voltage should be between 30 mV to 300 mV over all operational temperature, including the

If the load current exceeds the over current limit, the voltage will begin to drop. If the over current conditions

continues the output voltage will fall below the under voltage protection threshold and the TPS53125 will shut

down.

In an over current condition, the current to the load exceeds the current to the output capacitor; thus the output

voltage tends to fall off. Eventually, it will end up with crossing the under voltage protection threshold and

shutdown.

Over/Under Voltage Protection

TPS53125 monitors a resistor divided feedback voltage to detect over and under voltage. If the feedback voltage

is higher than 115% of the reference voltage, the OVP comparator output goes high and the circuit latches the

high-side MOSFET driver OFF and the low-side MOSFET driver ON.

When the feedback voltage is lower than 70% of the reference voltage, the UVP comparator output goes high

and an internal UVP delay counter begins counting. After 30

μs, TPS53125 latches OFF both top and bottom

reset when EN goes low level.

UVLO Protection

TPS53125 has V5FILT under voltage lock out protection (UVLO) that monitors the voltage of V5FILT pin.

When the V5FILT voltage is lower than UVLO threshold voltage, the device is shut off. All output drivers are OFF

and output discharge is ON. The UVLO is non-latch protection.

Thermal Shutdown

The TPS53125 includes an over temperature protection shut-down feature. If the TPS53125 die temperature

exceeds the OTP threshold (typically 150°C), both the high-side and low-side drivers are shut off, the output

voltage discharge function is enabled and then the device is shut off until the die temperature drops. Thermal

shutdown is a non-latch protection.

10

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