AMS3132 datasheet(8/10 Pages) AMS

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AMS3132

3A Fast Transient Linear Regulator

02/11/2010

www.advanced-monolithic.com

Phone (925) 443-0722

Fax (925) 443-0723

Device Summary

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.

Shutdown/Enable

The Enable (on/off) input threshold voltage is 1.2V.

When disabled the LDO quiescent current decreases

to a typical value of <1µA.

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.

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

error amplifier. To set the output voltage a

programming resistor from the adjust pin (ADJ) to

ground must be selected (See Pg.1). A 10kΩ 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:

R2=

Vout

Vref

-1

·R1 =

0.6V

-1

·10kΩ=73.2kΩ

Table 1: Adjustable Feedback Resistor values

Vout (V)

R2 (kΩ)

(R1=10kΩ)

1.8

20.0

2.5

31.6

3.3

45.3

5.0

73.2

Power Good Version

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 10KΩ is recommended at this

output. The pin can be left disconnected if unused.

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.

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

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

The internal losses contribute to the junction

temperature rise above the paddle and PCB

temperature.

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