AAT3258
300mA LDO Linear Regulator with µP Reset
The microprocessor reset section monitors the supply
asserted for a minimum of 150ms after VDET has risen
above the threshold, as shown in Figure 1.
voltage to a microprocessor and asserts a reset sig-
nal whenever the VDET voltage falls below a factory-
programmed threshold. This threshold is accurate
within +/-1.5% at 25°C. The reset signal remains
To assure the maximum possible performance is
obtained from the AAT3258, please refer to the fol-
lowing application recommendations.
VTH
VTH
VTH
VDET
tRDY
tRDY
RESET
Figure 1: Reset Signal Assertion.
Output Capacitor
LDO Regulator Applications
For proper load voltage regulation and operational
stability, a capacitor is required between pins VOUT
and GND. The COUT capacitor connection to
the LDO regulator ground pin should be made as
direct as practically possible for maximum device
performance.
Input Capacitor
Typically, a 1µF or larger capacitor is recommend-
ed for CIN in most applications. A CIN capacitor is
not required for basic LDO regulator operation.
However, if the AAT3258 is physically located more
than three centimeters from an input power source,
a CIN capacitor will be needed for stable operation.
CIN should be located as closely to the device VIN
pin as practically possible. CIN values greater than
1µF will offer superior input line transient response
and will assist in maximizing the highest possible
power supply ripple rejection.
The AAT3258 has been specifically designed to func-
tion with very low ESR ceramic capacitors. For best
performance, ceramic capacitors are recommended.
Typical output capacitor values for maximum output
current conditions range from 1µF to 10µF.
Applications utilizing the exceptionally low output
noise and optimum power supply ripple rejection
characteristics of the AAT3258 should use 2.2µF or
greater for COUT. If desired, COUT may be increased
without limit.
Ceramic, tantalum, or aluminum electrolytic capaci-
tors may be selected for CIN. There is no specific
capacitor ESR requirement for CIN. However, for
300mA LDO regulator output operation, ceramic
capacitors are recommended for CIN due to their
inherent capability over tantalum capacitors to with-
stand input current surges from low impedance
sources such as batteries in portable devices.
In low output current applications where output
load is less than 10mA, the minimum value for
COUT can be as low as 0.47µF.
3258.2006.03.1.6
11
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
