logic low, TPS61376 will scale the ISO FET to increase the on resistance to improve the input average current

accuracy. Meanwhile with ISEL pin logic low, the peak switching current limit will change from 4.5 A(typ) to 2.5

A(typ). The relationship between the input average current limit and the resistor is shown in Equation 3 and

Equation 4.

ILIM=43.2KRLIM  withISELpinlogichigh

(3)

ILIM=10.8KRLIM  withISELpinlogiclow

(4)

where

• RLIM is the resistance between the ILIM pin and the AGND pin.

• ILIM is the input average current limit.

For instance, the input average current limit is 3.0 A if the RLIM is 14.4 kΩ with ISEL pin logic high. This pin

cannot be left floating or connected to VCC.

8.3.6 Shut Down and Load Disconnect

When the input voltage is below the UVLO threshold or the EN pin is pulled low, The TPS61376 is in shutdown

mode and all the functions are disabled. The TPS61376 integrates a load disconnect function, the ISO FET

between the VP and SW pin will completely cut off the path between input and output when the device is

disabled.

8.3.7 Overvoltage Protection

If the output voltage at the VOUT pin is detected above 27.5 V (typ), the TPS61376 stops switching immediately

until the voltage at the VOUT pin drops the hysteresis value lower than the output overvoltage protection

threshold. This function prevents overvoltage on the output and secures the circuits connected to the output from

excessive overvoltage.

8.3.8 Thermal Shutdown

A thermal shutdown is implemented to prevent damages due to excessive heat and power dissipation. Typically,

the thermal shutdown happens at a junction temperature of 150°C. When the thermal shutdown is triggered, the

device stops switching until the junction temperature falls below typically 130°C, then the device starts switching

again.

8.4 Device Functional Modes

8.4.1 PWM Mode

The TPS61376 operates at a quasi-constant frequency pulse width modulation (PWM) in moderate to heavy

load condition before trigger the input average current limit. Based on the VIN to VOUT ratio, a circuit predicts

the required off-time of the switching cycle. At the beginning of each switching cycle, the low-side N-MOSFET

switch, shown in Functional Block Diagram, is turned on, and the inductor current ramps up to a peak current

that is determined by the output of the internal error amplifier. After the peak current is reached, the current

comparator trips, then it turns off the low-side N-MOSFET switch and the inductor current goes through the

schottky diode. Because the output voltage is higher than the input voltage, the inductor current decreases. Until

the calculated off-time is reached the low-side switch turns on again and the switching cycle is repeated.

8.4.2 Auto PFM Mode

The TPS61376 provides a seamless transition from PWM to PFM operation with smooth on-time/off-time (SOO)

mode and enables automatic pulse-skipping mode that provides excellent efficiency over a wide load range. As

load current decreasing or VIN rising, the output of the internal error amplifier decreases to lower the inductor

peak current, delivering less power to the load. When the output of the error amplifier goes down and reaches

a threshold of about 350-mA peak current, the output of the error amplifier is clamped at this value and does

not decrease any more, the TPS61376 extends its off-time of the switching period to deliver less energy to the

output and regulate the output voltage to the target.

TPS61376

SLVSGQ1A – JANUARY 2022 – REVISED SEPTEMBER 2022

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