MIC35152 Datasheet, PDF (7/8 Pages) Micrel Semiconductor – 1.5A, Low Voltage μCap LDO Regulator

Micrel, Inc.
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 MIC35152 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 MIC35152 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 MIC35152 regulator is specified between finite
loads. If the output current is too small, leakage currents
load current is necessary for proper operation.
MIC35152
dominate and the output voltage rises. A 10mA minimum
Enable Input
The MIC35152 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,
but can be connected to up to V_IN. When enabled, it
draws approximately 15µA.
Adjustable Regulator Design
Figure 1. Adjustable Regulator with Resistors
The MIC35152 allows programming the output voltage
anywhere between 1.24V and the 5.4V. Two resistors
are used. The resistor values are calculated by:
R1
=
R2
×
⎜⎜⎝⎛
V_OUT
1.240
−
1_{⎟⎟⎠⎞}
Where V_OUT 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
above).
October 2009
7
M9999-102309-A