LD3980

Detailed description

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Detailed description

The device is a low-dropout, low quiescent current linear regulator designed primarily for

battery-powered applications. It supplies a regulated output voltage for load currents up to

300mA. The LD3980 consists of a precision bandgap, error amplifier, output p-channel

MOS. The 0.7V bandgap reference is connected to the error amplifier. The error amplifier

compares this reference to the feedback voltage and amplifies the difference. The MOSFET

driver reads the error signal and applies the appropriate drive to the P-channel pass

transistor. If the feedback voltage is lower than reference voltage, the pass transistor is

pulled lower, allowing more current to pass and increasing the output voltage. If the

feedback voltage is higher than the reference voltage, the pass transistor gate is driven

higher, allowing less current to pass the output. The output voltage is feedback through an

internal resistor voltage connected to OUT. Additional blocks include an output current

limiter, a thermal sensor and shutdown logic.

6.1

Shutdown

Drive SHDN low to place the LD3980 in shutdown mode for DFN versions.

In shutdown mode, the pass transistor, control circuit, reference and all biases are turned

off, reducing the supply current to typically 0.5µA. Connecting SHDN to IN every block is in

normal operation.

6.2

Current limit

The device includes short-circuit protection. It includes a current limiter that controls the

pass transistor's gate voltage to limit the output current to about 600mA.

6.3

Thermal overload protection

The Thermal over load protection limits total power dissipation in the device. When the

shutdown logic, turning off the pass transistor and allowing the device to cool. The pass

transistor turns on again after the device's junction temperature typically cools by 15°C,

resulting in a pulsed output during continuous thermal overload conditions.

6.4

Power dissipation

Maximum power dissipation of the LD3980 depends on the thermal resistance of the case

and circuit board, the temperature difference between the die junction and ambient air, and

the rate of air flow. The power dissipated by the device is:

The maximum power dissipation is: