AAT2689 Datasheet, PDF (13/20 Pages) Advanced Analogic Technologies – PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters

PRODUCT DATASHEET
AAT2689
SystemPower^TM PMIC Solution for 12V Adapter Systems with 2-Output High Performance Step-Down Converters
Channel 1 Thermal Protection
The AAT2689 has an internal thermal protection circuit
which will turn on when the device die temperature
exceeds 135°C. The internal thermal protection circuit
will actively turn off the high side regulator output device
to prevent the possibility of over temperature damage.
The Buck regulator output will remain in a shutdown
state until the internal die temperature falls back below
the 135°C trip point. The combination and interaction
between the short circuit and thermal protection sys-
tems allows the Buck regulator to withstand indefinite
short-circuit conditions without sustaining permanent
damage.
Over-Current Protection
The Output 1 controller provides true-load DC output
current sensing which protects the load and limits com-
ponent stresses. The output current is sensed through
the DC resistance in the output inductor (DCR). The con-
troller reduces the operating frequency when an over-
current condition is detected; limiting stresses and pre-
venting inductor saturation. This allows the smallest
possible inductor for a given output load. A small resistor
divider may be necessary to adjust the over-current
threshold and compensate for variation in inductor DCR.
The preset current limit threshold is triggered when the
differential voltage from RS1 to OS1 exceeds 100mV
(nominal).
V _OUT1
L1
3.3V/2.5A
LX1
4.7μH 5.3A
R2
2k
RS1 ⁴
OS1 ⁵
C7
220nF
R7
R8
Figure 2: Resistor Network to Adjust the Current
Limit Less than the Pre-Set Over-Current
Threshold (Add R7, R8).
V_OUT1
L1
3.3V/2.5A
LX1
4.7μH 5.3A
R2
2k
RS1 ⁴
OS1 ⁵
C7
220nF
R6
R7
Figure 3: Resistor Network to Adjust the Current
Limit Greater than the Pre-Set Over-Current Level
(Add R6, R7).
Channel 2 Input Capacitor
Typically, a 1μF or larger capacitor is recommended for
C_IN in most applications. A C_IN capacitor is not required for
basic LDO regulator operation. However, if the AAT2689
is physically located more than three centimeters from an
input power source, a C_IN capacitor will be needed for
stable operation.
C_IN should be located as close to the device V_IN pin as pos-
sible. C_IN values greater than 1μF will offer superior input
line transient response and will assist in maximizing the
highest possible power supply ripple rejection. Ceramic,
tantalum, or aluminum electrolytic capacitors may be
selected for C_IN. There is no specific capacitor ESR require-
ment for C_IN. However, for 150mA LDO regulator output
operation, ceramic capacitors are recommended for C_IN
due to their inherent capability over tantalum capacitors
to withstand input current surges from low impedance
sources, such as batteries in portable devices.
Channel 2 Output Capacitor
For proper load voltage regulation and operational stabil-
ity, a capacitor is required between pins VOUT and GND.
The C_OUT capacitor connection to the LDO regulator
ground pin should be connected as close as possible for
maximum device performance. The AAT2689 LDO has
been specifically designed to function with very low ESR
ceramic capacitors. For best performance, ceramic
capacitors are recommended.
2689.2008.06.1.0
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