AP7173

1.5A LOW DROPOUT LINEAR REGULATOR WITH

PROGRAMMABLE SOFT-START

AP7173 Rev. 7

12 of 16

OCTOBER 2009

DS31369

www.diodes.com

Application Note

(Continued)

ENABLE/SHUTDOWN

The EN pin can be used with standard digital signals or

1.1V turns the regulator on. Figure 30 shows an example

where an RC circuit is used to delay start the AP7173.

If not used, the EN pin can be connected to the VCC or IN pin

measures are taken for the EN pin.

Figure 30. Delayed Start Using an RC Circuit

to Enable AP7173

POWER-GOOD

The power-good (PG) pin is an open-drain output and can be

pulled up through a resistor of 10k

Ω to1MΩ to V

pulled to low by an internal MOSFET.

OVER-CURRENT AND SHORT-CIRCUIT PROTECTION

The AP7173 features a factory-trimmed, temperature and

supply voltage compensated internal current limit and an

over-current protection circuitry to protect the device against

overload conditions. It limits the device current to a typical

more current.

For more effective protection against short-circuit failure, the

AP7173 also includes a short-circuit foldback mechanism that

lowers the current limit to a typical value of 1.0A when the

THERMAL PROTECTION

Thermal shutdown limits the AP7173 junction temperature and

protects the device from damage as a result of overheating.

junction temperature rises to approximately +150

°C, allowing it

to cool down. When the junction temperature drops to

approximately +130

°C, the output is re-enabled. Therefore, the

thermal protection circuit may cycle on and off at a rate

dependent on the power dissipation, thermal resistance, and

ambient temperature.

POWER DISSIPATION

Thermal shutdown is intented to protect the AP7173 against

abnormal overheating. For normal operation, excessive power

dissipation should be avoided and good heatsinking should be

provided. Power dissipation in the device is the product of the

device dropout voltage and the load current,

As can be seen, power dissipation can be minimized by using

the lowest input voltage necessary to achieve the required

output voltage regulation.

To ensure that the device junction temperature does not

exceed the specified limit of 125

°C, an application should

provide heat conduction paths that have junction-to-ambient

thermal resistance lower than the calculated value here:

For the DFN package with exposed pad, the primary

conduction path for heat is through the exposed pad to the

printed circuit board (PCB). The pad should be attached to an

appropriate amount of copper PCB area to ensure that the

device does not overheat.