Micrel, Inc.

MIC35302

October 2009

7

M9999-102309-A

Input Capacitor

An input capacitor of 1.0µF or greater is recommended

when the device is more than 4 inches away from the

bulk and supply capacitance, or when the supply is a

battery. Small, surface-mount chip capacitors can be

used for the bypassing. The capacitor should be place

within 1” of the device for optimal performance. Larger

values will help to improve ripple rejection by bypassing

the input to the regulator, further improving the integrity

of the output voltage.

Transient Response and 3.3V to 2.5V, 2.5V to 1.8V or

1.65V, or 2.5V to 1.5V Conversions

The MIC35302 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 10µF tantalum capacitor, 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, 2.5V to

1.8V or 1.65V, or 2.5V to 1.5V, 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 MIC35302 regulator will provide excellent

performance with an input as low as 3.0V or 2.25V,

respectively. This gives the PNP-based regulators a

distinct advantage over older, NPN-based linear

regulators.

Minimum Load Current

The MIC35302 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 operation.

Enable Input

The MIC35302 also 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,

draws approximately 15µA.

Adjustable Regulator Design

Figure 1. Adjustable Regulator with Resistors

The MIC35302 allows programming the output voltage

anywhere between 1.24V and 5.4V. Two resistors are

used. The resistor values are calculated by:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

×

=

1

1.240

V

R2

R1

OUT

shows component definition. Applications with widely

varying load currents may scale the resistors to draw the

minimum load current required for proper operation (see

Minimum Load Current

section).