3A Low-Voltage Low-Dropout Regulator

LM39300/39301/39302

HTC

8

Minimum Load Current

The LM39300/1/2 regulator is specified between finite loads.

If the output current is too small, leakage currents dominate and the output voltage rises.

A 10mA minimum load current is necessary for proper regulation.

Transient Response and 3.3V to 2.5V Conversion

The LM39300/1/2 has excellent transient response to varia-tions in input voltage and load current. The device has

been designed to respond quickly to load current variations and input voltage variations. Large output capacitors are

not required to obtain this performance. A standard 47F output capacitor, preferably tantalum, is all that is required.

Larger values help to improve performance even further.By virtue of its low-dropout voltage, this device does not

saturate into dropout as readily as similar NPN-based de-signs. When converting from 3.3V to 2.5V, the NPN-based

regulators are already operating in dropout, with typical dropout requirements of 1.2V or greater. To convert down to

2.5V without operating in dropout, NPN-based regulators require an input voltage of 3.7V at the very least. The

LM39300/1/2 regulator will provide excellent performance with an input as low as 3.0V. This gives the PNP-based

regulators a distinct advantage over older, NPN-based linear regulators.

Error Flag

The LM39301 version features an error flag circuit which monitors the output voltage and signals an error condition

when the voltage drops 5% below the nominal output voltage. The error flag is an open-collector output that can sink

10mA during a fault condition.Low output voltage can be caused by a number of problems, including an overcurrent

fault (device in current limit) or low input voltage. The flag is inoperative during overtemperature shutdown.

Enable Input

The LM39301 version features an enable input for on/off control of the device. Its shutdown state draws “zero” current

(only microamperes of leakage). The enable input is TTL/ CMOS compatible for simple logic interface, but can be

connected to up to 20V. When enabled, it draws approxi-mately 15A.

Adjustable Regulator Design

The LM39302 allows programming the output voltage any-where between 1.25V and the 16V maximum operating

rating of the family. Two resistors are used. Resistors can be quite large, up to 1MΩ, because of the very high input

impedance and low bias current of the sense comparator: The resistor values are calculated by :

R1=R2(Vout/1.250-

1)

Where VO is the desired output voltage. Figure 1 shows component definition. Applications with widely varying load

currents may scale the resistors to draw the minimum load current required for proper operation (see below).