MIC39300 datasheet(13/24 Pages) MICROCHIP

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DS20006017B-page 13

MIC39300/01/02

good transient response and stability over temperature.

Aluminum electrolytics can also be used, as long as the

ESR of the capacitor is < 1Ω.

The value of the output capacitor can be increased

without limit. Higher capacitance values help to

improve transient response and ripple rejection and

reduce output noise.

4.3

Input Capacitor

An input capacitor of 1 µF or greater is recommended

when the device is more than 4 inches away from the

bulk AC supply capacitance or when the supply is a

battery. Small, surface mount, ceramic chip capacitors

can be used for bypassing. Larger values will help to

improve ripple rejection by bypassing the input to the

regulator, further improving the integrity of the output

voltage.

4.4

Transient Response and 3.3V to

2.5V and 2.5V to 1.8V Conversions

The MIC39300/1/2 has excellent transient response to

variations 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 47 µF 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

designs. When converting from 3.3V to 2.5V or 2.5V to

1.8V, 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 MIC39300/1

regulator will provide excellent performance with an

input as low as 3.0V or 2.5V. This gives the PNP-based

regulators a distinct advantage over older, NPN-based

linear regulators.

4.5

Minimum Load Current

The MIC39300/1/2 regulators are specified between

finite loads. If the output current is too small, leakage

currents dominate and the output voltage rises. A

10 mA minimum load current is necessary for proper

regulation.

4.6

Error Flag

The MIC39301 version features an error flag circuit that

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 10 mA 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.

When the error flag is not used, it is best to leave it

open. A pull-up resistor from FLG to either VIN or VOUT

is required for proper operation.

4.7

Enable Input

The MIC39301/2 feature an enable input for on/off

control of the device. The enable input’s 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 approximately 15 µA.

4.8

Adjustable Regulator Design

FIGURE 4-2:

Adjustable Regulator with

Resistors.

The MIC39302 allows programming the output voltage

anywhere between 1.24V and 15.5V. Two resistors are

used. The resistor values are calculated by:

EQUATION 4-3:

Where VOUT is the desired output voltage. Figure 4-2

shows the component deﬁnition. Applications with

widely varying load currents may scale the resistors to

draw the minimum load current required for proper

operation (see the Minimum Load Current section).

VOUT

VIN

COUT

OUT

ADJ

GND

MIC39302

ENABLE

SHUTDOWN

VOUT = 1.240V (1 +

)

VOUT

1.240

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