DIA7976

Version 1.9, Apr 2025

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© 2025 Dioo Microcircuits Co., Ltd. Jiangsu

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9. Function Description

9.1.Overview

The DIA7976 is a low-dropout regulator (LDO) that consumes a low quiescent current and delivers an

excellent line and load transient performance. These characteristics, combined with low noise and high

PSRR with low dropout voltage, make this device ideal for automotive applications.

This regulator offers short-current limit, shutdown, and thermal protection. The operating junction temperature

for this device is -40°C to 150°C.

9.2.Undervoltage lockout (UVLO)

The DIA7976 contains an undervoltage lockout (UVLO) circuit that ensures that the device is functional when the

supply voltage is lower than the operational range of the internal circuitry, which disables the output until the

input voltage is greater than the rising UVLO voltage (VUVLO). When VIN is less than VUVLO, the output is

connected to the ground with a pulldown resistor (RPULLDOWN). When the device enters UVLO, the PG output is

pulled low.

9.3.Shutdown

The enable pin (EN) is active high. Forcing the EN pin to exceed VEN(HI) will enable the device forcing the EN pin

to drop below VEN(LO) will turn off the device. Connect EN to IN when shutdown capability is not required. The PG

output pin is pulled low when the device is disabled. The DIA7976 has an internal pulldown MOSFET that

connects an RPULLDOWN resistor to the ground when the device is disabled. Output capacitance (COUT) and the

load resistance (RL) in parallel with the pulldown resistor (RPULLDOWN ) decide the discharge time after disabling.

The equation below calculates the time constant:

T = ( RPULLDOWN × RL)/(RPULLDOWN + RL) × COUT

(1)

9.4.Current limit

The device is protected during transient high-load current faults or shorting events by an internal current limit

circuit. The current limit is a hybrid scheme that transitions from a current-limit scheme to a short-limit scheme at

the voltage about 0.3 V. When the output is shorted, the device supplies a typical current called the short-circuit

current limit (ISC). In a high-load current fault with the output voltage above 0.3 V, the current-limit scheme limits

the output current to ICL. When the voltage drops below 0.3 V, a short-current limit activates that scales back the

current as the output voltage approaches GND.

When the device is within the current limit, the output voltage is not regulated. The device begins to heat up

when a current limit event occurs, and if a thermal shutdown is triggered, the device turns off. When the device is

in current-limit, the pass transistor dissipates power [(VIN - VOUT) × ICL]. When the device output is shorted and

the output is below 0.3 V, the pass transistor dissipates power [(VIN - VOUT) × ISC]. The internal thermal shutdown

circuit turns the device back on after the device cools down. The device cycles between the current limit and

thermal shutdown if the output current fault condition continues.