Third Stage (Power Stage)

This last stage delivers 30dBm to a 50Ω load. It oper-

ates in Class E to achieve a high power-added efficiency

(PAE). Proper output matching is required for optimal

output power. The output of the power stage requires a

low-series-resistance pull-up inductor with a minimum

current rating of 1.5A. See the Typical Operating Circuit

for an example of an output matching circuit.

Biasing and Power Control

SHDN

, GC, RAMP, and REF are bias and power-control

pins. Drive SHDN below 0.5V to turn off the entire chip,

and drive SHDN above 2.0V to turn on the device. When

SHDN

is high, a VGC from 0.6V to 2.3V continuously

controls the gain in the first stage (VGA) and the output

power.

Drive GC below 0.4V to put the device in standby mode

with only the first stage on. If GC is unconnected and

VSHDN > 2.0V, the device is set to maximum gain. Table

1 summarizes these operating modes.

Power Ramping Control

A capacitor connected between RAMP and REF controls

the output power rise/fall time to reduce transient noise

when SHDN turns the device on and off. Because the

ramp is approximately a raised cosine, this device can

be used in direct On/Off Keying (OOK) applications with

minimum intersymbol interference. The value of the ramp-

ing capacitor is determined from the Rise/Fall Time vs.

Ramping Capacitance curves in the Typical Operating

Characteristics.

Board Assembly Precaution

Solder the underside metal slug evenly to the board

ground plane for optimal performance. Fill all vias in

the area under the slug. For maximum power gain and

saturated output power, ensure that the entire slug makes

contact with the board ground.

Table 1. Data Output Format

SHDN

GC

MODE

>2.0V

>0.6V

On

>2.0V

<0.4V

Standby

<0.5V

Don’t care

Shutdown

PACKAGE TYPE

DOCUMENT NO.

22-pin TSSOP

21-0108

www.analog.com

Analog Devices │ 7

MAX2235

+3.6V, 1W Autoramping Power

Amplifier for 900MHz Applications

Chip Information

TRANSISTOR COUNT: 668

Package Information

For the latest package outline information and land patterns

(footprints), go to

www.maximintegrated.com/packages. Note

that a “+”, “#”, or “-” in the package code indicates RoHS status

only. Package drawings may show a different suffix character, but

the drawing pertains to the package regardless of RoHS status.