6

Application information

6.1

Thermal and short-circuit protections

The LD39200 is self-protected from short-circuit conditions and overtemperature. When the output load is higher

than the one supported by the device, the output current rises until the limit of typically 3.5 A is reached; at this

point the current is kept constant even when the load impedance is zero. The thermal protection acts when the

junction temperature reaches 170 °C. The IC enters the shutdown status. As soon as the junction temperature

falls again below 150 °C the device starts working again. In order to calculate the maximum power the device can

dissipate, keeping the junction temperature below TJ-OP , the following formula is used:

PDMAX= 125−TAMB /RTHJ−A

(1)

6.2

Output voltage setting for ADJ version

In the adjustable version, the output voltage can be set from 0.5 V up to the input voltage minus the voltage drop

across the pass transistor (dropout voltage), by connecting a resistor divider between the ADJ pin and the output,

allowing remote voltage sensing. The resistor divider can be selected using the following equation:

VOUT=VADJ1+R1/R2,witℎVADJ=0.5V typ.

(2)

6.3

Enable pin

The LD39200 features an enable function. When the EN voltage is higher than 1.2 V the device is ON, and if it is

lower than 0.5 V the device is OFF. In shutdown mode, the total current consumption is 10 nA (typ). The EN pin

does not have an internal pull-up, therefore it cannot be left floating if it is not used.

6.4

Power Good pin (PG)

Some applications require a flag showing that the output voltage is in the correct range. Power Good threshold

depends on the output voltage. When the output voltage is higher than 0.92 * VOUT(nom), the PG pin goes to high

impedance. If the output voltage is below 0.80 * VOUT(nom) the PG pin goes to low impedance. If the device works

well, the PG pin is at high impedance.

6.5

Reverse current protection

The device avoids the reverse current to flow from the output to the input during any operating condition (EN = 0

or EN = 1, VIN > VOUT + VDROP). During fast turn-on/off this function prevents a big current from flowing to the

input. Moreover it is used to avoid the reverse current to flow from the output pin to the input one, when other

power supplies, providing a voltage higher than the input voltage, are connected to the output pin. If a power

supply, providing a voltage lower than LDO output voltage, is connected to OUT pin, LDO works in current

protection, causing high power dissipation inside the device.

When the device is disabled (EN = low) and VOUT > 0 V, a small current (few µA) is sunk from the OUT pin.

LD39200

Application information

DS10079 - Rev 3

page 9/29