AAT2506 Datasheet, PDF (14/26 Pages) Advanced Analogic Technologies – 1MHz Step-Down Converter/LDO Regulator

AAT2506
1MHz Step-Down Converter/LDO Regulator
VIN
C3
10µF
VOUTLDO
C4
4.7µF
C5
10nF
3
VP
4
VCC
5
VLDO
10
EN
9
2
ENLDO LX
6
OUT
11
FB
7
12
BYP SGND
8
1
GND PGND
U1
AAT2506
L1
VOUTBUCK
C1
22µF
VIN
C3
10µF
VOUTLDO
C4
4.7µF
C5
10nF
3
VP
4
VCC
5
VLDO
10
EN
9
ENLDO
2
LX
6
OUT
11
FB
7
BYP
12
SGND
8
1
GND PGND
U1
AAT2506
L1
VOUTBUCK
R1
C8
100pF
R2
59k
C1
22µF
Figure 1: AAT2506 Fixed Output.
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_DS(ON).
Low Supply
The under-voltage lockout (UVLO) guarantees suf-
ficient V_IN bias and proper operation of all internal
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
Figure 2: AAT2506 with Adjustable Step-Down
Output and Enhanced Transient Response.
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 AAT2506 is physically locat-
ed more than three centimeters from an input
power source, a C_IN capacitor will be needed for
stable operation. Typically, a 1µF or larger capaci-
tor is recommended for C_IN in most applications.
C_IN should be located as closely to the device V_IN
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_IN. There is no specific capacitor ESR
requirement for C_IN. However, for 300mA LDO reg-
ulator output operation, ceramic capacitors are rec-
ommended for C_IN due to their inherent capability
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_OUT capacitor connection to the LDO
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
2506.2005.12.1.0