AMS3132
3A Fast Transient Linear Regulator
Device Summary
Table 1: Adjustable Feedback Resistor values
R2 (kΩ)
(R1=10kΩ)
The AMS3132 is a high voltage low drop out linear
regulator with a current capability of up to 3A. The
LDO has a recommended operating input voltage
range of 1.5V to 7V with an output voltage as low as
0.6V and is stable with a wide range of ceramic,
tantalum, and electrolytic output capacitors.
Vout (V)
1.8
20.0
31.6
45.3
73.2
2.5
3.3
5.0
Shutdown/Enable
Power Good Version
The Enable (on/off) input threshold voltage is 1.2V.
When disabled the LDO quiescent current decreases
to a typical value of <1µA.
During operation, fault conditions can occur
unexpectedly. Such conditions include input voltage
dropout (low VIN), overheating, or overloading
(excessive output current). If any of these conditions
occurs, the PG pin will set an “error flag”. The PG pin,
which is an open-collector output, will go LOW when
VOUT is less than 95% or the specified output voltage.
When the voltage at VOUT is greater than 95% of the
specified output voltage, the PG pin is HIGH. A logic
pull-up resistor of 10Kꢀ is recommended at this
output. The pin can be left disconnected if unused.
Fault Protection
Short circuit and over-temperature shutdown disable
the converter and LDO in the event of an overload
condition. Over-temp shutdown disables the device
when the junction temperature exceeds 145 ºC. The
output current is internally limited to 6A typical.
Input Capacitor
An input bypass capacitor ranging from 1µF to 22µF
is required. The capacitor should be placed as close
as possible to the device and not be placed more than
1 inch from the LDO.
PCB Layout
The following guidelines should be followed to insure
proper layout.
1. VIN Capacitor. A low ESR ceramic bypass
capacitor must be placed as close to the IC as
possible.
2. Adjustable (ADJ) Feedback Resistors. The
adjustable feedback resistors should be placed as
close as possible the IC. Minimize the length of
the trace from the feedback pin to the resistors.
This is a high impedance node susceptible to
interference from external RF noise sources
3. Ground.
Output Capacitor
The output capacitor requirements range from the
minimum value required to guarantee stability to
larger values required to meet the extreme transient
response requirements. Values range from 10 to
22µF X5R ceramic capacitors. Due to the extreme
voltage coefficient of X5R ceramic capacitors, the
voltage rating should be at least double the maximum
applied voltage.
Adjustable Version: Feedback Resistor Selection
Choosing AMS3132 with adjustable output voltage
option allows the user to select an output voltage by
using an external resistor divider. AMS 3132 uses a
0.6V reference voltage at the positive terminal of the
4. For good thermal performance vias are required
to couple the tab of the TO-263 package to the
PCB ground plane. The via diameter should be
0.3mm to 0.33mm positioned on a 1.2mm grid.
Output Power and Thermal Limits
error amplifier. To set the output voltage
a
programming resistor from the adjust pin (ADJ) to
ground must be selected (See Pg.1). A 10kꢀ resistor
is a good selection for a programming resistor R1. A
higher value may result in an excessively sensitive
feedback node while a lower value will draw more
current and degrade the light load efficiency. The
equation for selecting the voltage specific resistor is:
The AMS3132 junction temperature and current
capability depends on the internal dissipation and the
junction to case thermal resistance of the TO-263
exposed tab packages. Additionally, the tab paddle
and PCB temperature will be elevated due to the total
losses of the LDO and of other circuits mounted to the
PCB.
Tjmax=Pd·θjc+Tpcb+Tamb
5V
R2=ꢀVVoreuft -1ꢁ ·R1 =ꢀ0.6V -1ꢁ ·10kꢀ=73.2kꢀ
The internal losses contribute to the junction
temperature rise above the paddle and PCB
temperature.
02/11/2010
www.advanced-monolithic.com
Phone (925) 443-0722
Fax (925) 443-0723
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