GND

R3

R1

C4

C3

C2

GND

R4

V+

+INB

-INB

OUTB

V+

SDB

SDA

V-

+INA

-INA

OUTA

VOUT

VIN

ShutDown

VOUT

ShutDown

VIN

V-

GND

R2

C1

Copyright © 2016, Texas Instruments Incorporated

22

LMV712-N, LMV712-N-Q1

SNOS534J – FEBRUARY 2001 – REVISED NOVEMBER 2016

www.ti.com

Product Folder Links: LMV712-N LMV712-N-Q1

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Copyright © 2001–2016, Texas Instruments Incorporated

Typical Applications (continued)

8.2.3.2 Detailed Design Procedure

There are four critical sections in the GSM Power Amplifier Control Loop. The class-C RF power amplifier

provides amplification of the RF signal. A directional coupler couples small amount of RF energy from the output

of the RF P. A. to an envelope detector diode. The detector diode senses the signal level and rectifies it to a DC

level to indicate the signal strength at the antenna. An op amp is used as an error amplifier to process the diode

voltage and ramping voltage. This loop control the power amplifier gain through the op amp and forces the

detector diode voltage and ramping voltage to be equal. Power control is accomplished by changing the ramping

voltage.

The LMV712-N is well suited as an error amplifier in this application. The LMV712-N has an extra shutdown pin

to switch the op amp to shutdown mode. In shutdown mode, the LMV712-N consumes very low current.

Therefore, the power amplifier can be turned off to save battery life. The LMV712-N output is tri-stated when in

shutdown.

9 Power Supply Recommendations

For proper operation, the power supplies must be properly decoupled. For decoupling the supply lines, TI

recommends that 10-nF capacitors be placed as close as possible to the power supply pins of the operational

amplifier. For single supply, place a capacitor between V+ and V– supply leads. For dual supplies, place one

capacitor between V+ and ground, and one capacitor between V– and ground.

10 Layout

10.1 Layout Guidelines

To properly bypass the power supply, several locations on a printed circuit board must be considered. A 6.8 µF

or greater tantalum capacitor must be placed at the point where the power supply for the amplifier is introduced

onto the board. Another 0.1-µF ceramic capacitor must be placed as close as possible to the power supply pin of

the amplifier. If the amplifier is operated in a single power supply, only the V+ pin requires bypassing with a 0.1-

µF capacitor. If the amplifier is operated in a dual power supply, both V+ and V– pins must be bypassed.

It is good practice to use a ground plane on a printed circuit board to provide all components with a low inductive

ground connection.

Surface mount components in 0805 size or smaller are recommended in the LMV712-N application circuits.

Designers can take advantage of the DSBGA, WSON, and VSSOP miniature sizes to condense board layout to

save space and reduce stray capacitance.

10.2 Layout Example

Figure 38. Sample Layout of VSSOP