6

Device functional description

The LEO3910 adjustable voltage regulator contains a PNP type power element controlled by a signal resulting

from an amplified comparison between the internal temperature-compensated band-gap and the fraction of the

desired output voltage value obtained from an external resistor divider bridge. The device is protected by several

functional blocks.

6.1

ADJ pin

The output voltage feedback comes through an external resistor divider (R1, R2 as in the typical application

schematic), whose mid-point connected to the ADJ pin (allowing all possible output voltage settings as per user

requirements).

6.2

INHIBIT

By setting the INHIBIT pin TTL high, the device switches off the output current and voltage. The device is ON

when the INHIBIT pin is set low. Since the INHIBIT pin is pulled down internally, it can be left floating in cases

where the inhibit function is not used.

6.3

Overtemperature protection

The LEO3910 is protected by a junction temperature detection circuit, turning the device “OFF” when the

temperature attains 175 °C. The recovery of the ON mode occurs with a hysteresis of 40 °C. Combined with

the other protection blocks, the device is protected from destructive junction temperature excursions in all load

conditions. It should be noted that when the internal temperature detector reaches 175 °C, the active power

element can be as high as 225 °C. Prolonged operation under these conditions far exceeds the maximum

operating ratings and the device reliability cannot be guaranteed.

6.4

Overcurrent protection

The device is equipped with a circuit having the purpose of limiting the maximum load current, in order to protect

the output stage against possible overcurrent-related damages. By denoting ISHORT the maximum current

available at output, this value can be modified externally by a resistor between the pins ISC and Vin, with a typical

value range of 17 kΩ to 200 kΩ.

As the behavior of the overcurrent protection, when the load current approaches the mentioned ISHORT, the

regulation is inhibited.

To maintain optimal VO regulation and at the same time an acceptable accuracy for ISHORT, it is necessary:

•

to set an ISHORT> = 1 A

•

regulation range.

When IO reaches typically ISHORT – 300 mA, the current limiter overrules the regulation, VO starts to drop and

the OCM flag rises. When no current limitation adjustment is required, the ISC pin can be left unbiased.

6.5

OCM pin

In the event of an overcurrent at the output, a voltage level of 0.4 V is present at the OCM pin. In other conditions,

up to 10 mA.

LEO3910

Device functional description

DS13691 - Rev 2

page 7/21