AAT2500 Analogic Corporation, AAT2500 Datasheet - Page 14

• Manufacturer Part Number: AAT2500
• Manufacturer: Analogic Corporation

Low Dropout Operation
For conditions where the input voltage drops to the
output voltage level, the converter duty cycle
increases to 100%. As 100% duty cycle is
approached, the minimum off-time initially forces
the high side on-time to exceed the 1MHz clock
cycle and reduce the effective switching frequency.
Once the input drops below the level where the out-
put can be regulated, the high side P-channel
MOSFET is turned on continuously for 100% duty
cycle. At 100% duty cycle, the output voltage tracks
the input voltage minus the IR drop of the high side
P-channel MOSFET R
Low Supply
The under-voltage lockout (UVLO) guarantees suf-
ficient V
circuitry prior to activation.
Fault Protection
For overload conditions, the peak inductor current is
limited. Thermal protection disables switching when
the internal dissipation or ambient temperature
becomes excessive. The junction over-temperature
threshold is 140°C with 15°C of hysteresis.
14
C4
4.7µF
V
OUTLDO
C3
10µF
V
IN
Figure 1: AAT2500 Fixed Output.
IN
bias and proper operation of all internal
C5
10nF
3
5
9
6
7
8
VP
VLDO
ENLDO
OUT
BYP
GND
U1
AAT2500
DS(ON)
SGND
PGND
VCC
EN
LX
FB
.
4
10
2
11
12
1
L1
V
OUTBUCK
1MHz Step-Down Converter/LDO Regulator
C1
4.7µF
Figure 2: AAT2500 with Adjustable Step-Down
Applications Information
Linear Regulator
Input and Output Capacitors: An input capacitor
is not required for basic operation of the linear reg-
ulator. However, if the AAT2500 is physically locat-
ed more than three centimeters from an input
power source, a C
stable operation. Typically, a 1µF or larger capaci-
tor is recommended for C
C
pin as practically possible.
An input capacitor greater than 1µF will offer supe-
rior input line transient response and maximize
power supply ripple rejection. Ceramic, tantalum,
or aluminum electrolytic capacitors may be select-
ed for C
requirement for C
ulator output operation, ceramic capacitors are rec-
ommended for C
over tantalum capacitors to withstand input current
surges from low impedance sources such as bat-
teries in portable devices.
For proper load voltage regulation and operational
stability, a capacitor is required between OUT and
GND. The C
regulator ground pin should be made as directly as
practically possible for maximum device perform-
ance. Since the regulator has been designed to
function with very low ESR capacitors, ceramic
capacitors in the 1.0µF to 10µF range are recom-
mended for best performance. Applications utilizing
Output and Enhanced Transient Response.
C4
4.7µF
IN
V
should be located as closely to the device V
C3
10µF
OUTLDO
V
IN
IN
C5
10nF
. There is no specific capacitor ESR
OUT
3
5
9
6
7
8
IN
capacitor connection to the LDO
IN
VP
VLDO
ENLDO
OUT
BYP
GND
. However, for 300mA LDO reg-
IN
U1
AAT2500
due to their inherent capability
capacitor will be needed for
SGND
PGND
VCC
EN
LX
FB
IN
4
10
2
11
12
1
in most applications.
L1
AAT2500
R2
59k
2500.2005.08.1.9
R1
C8
100pF
V
OUTBUCK
C1
4.7µF
IN