MAXIM MAX2235 Technical data

General Description

The MAX2235 low-voltage, silicon RF power amplifier
(PA) is designed for use in the 900MHz frequency band.
It operates directly from a single +2.7V to +5.5V supply,
making it suitable for use with 3-cell NiCd or 1-cell Li-Ion
batteries. The device delivers +30dBm (1W) typical out­put power from a +3.6V supply or +28dBm from a +2.7V
supply.

The MAX2235’s gain is adjustable over a 37dB range.
A power-control pin controls gain and bias to maintain
optimum efficiency, even at lower output power levels,
thus extending the operating life of the battery. At
+30dBm output power, efficiency is typically 47%. An
additional power-saving feature is a shutdown mode
that typically reduces supply current below 1µA.

A key feature of this PA is its autoramping capability.
During turn-on and turn-off periods, the RF envelope is
controlled to approximate a raised cosine on the rising
and falling edge, thereby minimizing transient noise
and spectral splatter. The ramp time is set by selecting
the value of an external capacitor.

The MAX2235 is intended for use in constant envelope
applications such as AMPS, two-way paging, or FSK­based communications in the 900MHz ISM band. The
device is available in a thermally enhanced 20-pin
TSSOP package with a heat slug.

Applications

900MHz ISM-Band Applications

Two-Way Pagers

Analog Cellular Phones

Microcellular GSM (Power Class 5)

Wireless Data Networks

Features

♦ 800MHz to 1000MHz Operation

♦ High Output Power at 836MHz

+32.5dBm at +5.0V
+30dBm at +3.6V
+29dBm at +3.0V
+28dBm at +2.7V

♦ +2.7V to +5.5V Single-Supply Operation

♦ Automatic Power-Up/Power-Down Ramp

♦ Direct On/Off Keying (OOK) without Intersymbol

Interference or VCO Pulling

♦ 37dB Power-Control Range

♦ 47% Efficiency

♦ <1µA Supply Current in Shutdown Mode

♦ Small 20-Pin TSSOP Package with Heat Slug

MAX2235

+3.6V, 1W Autoramping Power

Amplifier for 900MHz Applications

________________________________________________________________ Maxim Integrated Products 1

Functional Diagram

19-1463; Rev 2; 10/00

PART

MAX2235EUP -40°C to +85°C

TEMP. RANGE PIN-PACKAGE

20 TSSOP-EP

EVALUATION KIT

AVAILABLE

Pin Configuration

Ordering Information

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

V

CCVCCVCC

4 3 5 8, 9

11

RAMP

12

REF

SHDN

GC

RFIN

NOTE: SOLDER UNDERSIDE OF METAL SLUG TO BOARD GND PLANE.

BIAS

19

20

1

VGA

V

CC

MAX2235

6, 7, 102

RFOUT

15, 16

13, 14, 17, 18, SLUG

GNDGND GND

TOP VIEW

1

RFIN

2

GND

3

V

CC

4

CC

5

6

7

8

9

10

MAX2235

TSSOP-EP

V

CC

GND

GND

CC

V

CC

NOTE: THE GROUND OF THE OUTPUT STAGE IS CONNECTED TO THE
UNDERSIDE METAL SLUG.

20

GC

19

SHDN

18

GND

17

GNDV

16

RFOUT

15

RFOUT

14

GND

13

GNDV

12

REF

11

RAMPGND

MAX2235

+3.6V, 1W Autoramping Power
Amplifier for 900MHz Applications

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

DC ELECTRICAL CHARACTERISTICS

(VCC= +2.7V to +5.5V, GC = RAMP = REF = unconnected, no input signal applied, TA= -40°C to +85°C, unless otherwise noted.
Typical values are at V

CC

= +3.6V and TA= +25°C.)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

VCCto GND...........................................................-0.3V to +6.5V

SHDN to GND.............................................-0.3V to (V

CC

+ 0.3V)

GC to GND .................................................-0.3V to (V

CC

+ 0.3V)

RF Input Power .................................................+13dBm (20mW)

Maximum Load Mismatch without Damage,

V

CC

= +2.7V to +3.4V, Any Load Phase Angle,

Any Duration.......................................................................20:1

Maximum Load Mismatch without Damage,

V

CC

= +3.4V to +5.5V, Any Load Phase Angle,

Any Duration.........................................................................8:1

Continuous Power Dissipation (T

A

= +70°C)

TSSOP (derate 80mW/°C above T

A

= +70°C) ..................6.4W

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

SHDN = GND

(Note 1)

(Note 2)

V

SHDN

> 2.3V, VGC> 0.6V

V

SHDN

< 0.5V, VGC< 0.4V

2.7V < VCC< 3.4V, SHDN = GND,
T

A

= +55°C

V

SHDN

= 2.0V

V

SHDN

< 0.5V

CONDITIONS

0.5 100

V0.5V

IL

V2.0V

IH

SHDN Logic High
SHDN Logic Low

V2.0 2.2 2.4V

GCNOM

GC Open-Circuit Voltage

µA

-10 1.0

I

GC

GC Input Current

-0.5 0.5

I

SHDN

Shutdown Supply Current µA

2

0.5
µA

-0.5 0.5

I

INSHDN

SHDN Input Current

UNITSMIN TYP MAXSYMBOLPARAMETER

VGC< 0.4 mA20I

STBY

Standby Supply Current

MAX2235

+3.6V, 1W Autoramping Power

Amplifier for 900MHz Applications

_______________________________________________________________________________________ 3

Note 1: ≥ +25°C guaranteed by production test, <+25°C guaranteed by design and characterization.
Note 2: MAX guaranteed by production test, MIN guaranteed by design and characterization.
Note 3: Guaranteed by design and characterization.
Note 4: For optimum performance at a given frequency, design the output matching network for maximum output power.
Note 5: Gain is monotonic with V

GC

.

Note 6: 0.068µF capacitor from RAMP to REF. Time is measured from SHDN low-to-high transition to +29dBm output power, or

from SHDN high-to-low transition to -25dBm output power.

Note 7: Harmonics measured on the evaluation kit, which provides some harmonic attenuation in addition to the rejection provided

by the IC. The combined suppression is specified.

P

RFIN

adjusted to give P

RFOUT

= +24dBm

P

RFOUT

= +30dBm

P

RFIN

= 0dBm, VGCadjusted to give

P

RFOUT

= 24dBm

315

610

Average Supply Current

%47PAEPower Added Efficiency

0.6V < VGC< 2.3V dB37

dB24 26G

P

Power Gain

Gain-Control Range (Note 5)

mW/µs1.6dP/dt

Auto-Power Ramping-Up
Maximum Slope (Note 6)

Input VSWR relative to input impedance in
operating mode

VCC= 2.7V to 5.5V, 6:1 VSWR at any phase
angle

1.5:1∆VSWR

Standby Mode Input VSWR
Change

50Ω source impedance

dBc-60

Maximum Nonharmonic
Spurious Output Due to Load
Mismatch

1.5:1VSWRInput VSWR

mW/µs-1.3dP/dt

Auto-Power Ramping-Down
Minimum Slope (Note 6)

30kHz BW at offset = 45MHz dBm-90Noise Power

40 48

P

RFIN

= +7dBm dBc30 38Harmonic Suppression (Note 7)

mA

305

I

CC

P

RFIN

= 0dBm dB

25 36

Off-Isolation

V

SHDN

= 0.5V

GC = GND

AC ELECTRICAL CHARACTERISTICS

(MAX2235 Evaluation Kit, GC = unconnected, P

RFIN

adjusted to give P

RFOUT

= +30dBm, f

RFIN

= 836MHz, VCC= V

SHDN

= +3.6V,

T

A

= +25°C, unless otherwise noted.) (Note 3)

CONDITIONS UNITSMIN TYP MAXSYMBOLPARAMETER

VCC= 2.7V 28.0

VCC= 3.0V, TA= T

MIN

to T

MAX

25.5

VCC= 3.0V (Note 4)

27.0 28.7

VCC= 3.6V

30.3

VCC= 5.0V

dBm

32.5

P

RFOUT

Minimum Output Power

MHz

800 1000

f

RFIN

Operational Frequency Range
(Note 4)

MAX2235

+3.6V, 1W Autoramping Power
Amplifier for 900MHz Applications

4 _______________________________________________________________________________________

Typical Operating Characteristics

(MAX2235 Evaluation Kit, GC = unconnected, f

RFIN

= 836MHz, VCC= V

SHDN

= +3.6V, TA= +25°C, unless otherwise noted.)

0

200

100

400

300

600

500

700

010155 20253035

SUPPLY CURRENT vs. OUTPUT POWER

MAX2235 toc01

OUTPUT POWER (dBm)

I

CC

(mA)

TA = -40°C

TA = +25°C

TA = +85°C

-20

0

-10

20

10

30

40

0 1.00.5 1.5 2.0 2.5

OUTPUT POWER

vs. VOLTAGE AT GC PIN

MAX2235 toc02

VGC (V)

OUTPUT POWER (dBm)

P

RFIN

= 0dBm

TA = -40°C

TA = +25°C

TA = +85°C

0

10

5

20

15

30

25

35

-25 -15 -10-20 -5 0 5 10

OUTPUT POWER vs. INPUT POWER

MAX2235 toc03

INPUT POWER (dBm)

OUTPUT POWER (dBm)

VCC = +5.0V

VCC = +3.6V

VCC = +3.0V

VCC = +2.7V

0

10

5

20

15

30

25

35

-25 -15 -10-20 -5 0 5 10

OUTPUT POWER vs. INPUT POWER

AND TEMPERATURE

MAX2235 toc04

INPUT POWER (dBm)

OUTPUT POWER (dBm)

TA = -40°C

TA = +25°C

TA = +85°C

0

20

10

40

30

50

60

015205 10 253035

EFFICIENCY vs. OUTPUT POWER

MAX2235 toc07

OUTPUT POWER (dBm)

EFFICIENCY (%)

VCC = +5.0V

VCC = +3.6V

VCC = +3.0V

VCC = +2.7V

-60

-40

-50

-20

-30

-10

0

-25 -10 -5-20 -15 0 5 10

SECOND AND THIRD HARMONICS

vs. INPUT POWER

MAX2235 toc05

INPUT POWER (dBm)

HARMONIC POWER (dBm)

2nd

3rd

0

10

5

20

15

30

25

35

820 830 835825 840 845 850 855

OUTPUT POWER vs. FREQUENCY

MAX2235 toc06

INPUT FREQUENCY (MHz)

OUTPUT POWER (dBm)

P

RFIN

= +3dBm

P

RFIN

= -5dBm

P

RFIN

= -13dBm

P

RFIN

= -21dBm

MATCHED AT

836MHz

0

10

5

20

15

30

25

35

010155 20253035

POWER GAIN vs. OUTPUT POWER

MAX2235 toc08

OUTPUT POWER (dBm)

POWER GAIN (dB)

VCC = +5.0V

VCC = +3.6V

VCC = +3.0V

40

VCC = +2.7V

0

10

5

20

15

35

30

25

40

0105 1520253035

POWER GAIN vs. OUTPUT POWER

AND TEMPERATURE

MAX2235 toc09

OUTPUT POWER (dBm)

POWER GAIN (dB)

TA = -40°C

TA = +25°C

TA = +85°C

MAX2235

+3.6V, 1W Autoramping Power

Amplifier for 900MHz Applications

_______________________________________________________________________________________ 5

Typical Operating Characteristics (continued)

(MAX2235 Evaluation Kit, GC = unconnected, f

RFIN

= 836MHz, VCC= V

SHDN

= +3.6V, TA= +25°C, unless otherwise noted.)

0

400

200

800

600

1000

1200

0406020 80 100 120

FALL TIME vs. RAMPING CAPACITANCE

MAX2235 toc11

CAPACITANCE (nF)

FALL TIME (µs)

FULL POWER = +20dBm

FULL POWER = +10dBm

FULL POWER = +30dBm

NAME FUNCTION

1 RFIN

RF Input. A DC blocking capacitor in series with RFIN is required. The value of the capacitor depends on
the operating frequency.

PIN

Pin Description

2 GND

GND connection for the input stage (variable-gain amplifier). Connect to the circuit board ground plane
with a separate low-inductance path (via).

3 V

CC

Supply Voltage Input for the Input Stage. Bypass with its own 100pF low-inductance capacitor to GND.

4 V

CC

Supply Voltage Input for Bias Circuitry. Bypass with its own 100pF low-inductance capacitor and a 1000pF
capacitor to GND, to minimize RF signal coupling into the bias circuits.

5 V

CC

Supply Voltage Input for the Input Stage. Bypass with its own 22pF low-inductance capacitor to pins 6 and 7.

6, 7, 10 GND

GND Connection for the Second-Stage Amplifier (driver). Connect to the circuit board ground plane with a
separate low-inductance path (via).

8 V

CC

Supply Voltage Input for the Second Stage. Bypass with its own 220pF and 1000pF low-inductance
capacitors to GND.

9 V

CC

Supply Voltage Input for the Second Stage. Connect to pin 8.

11 RAMP

Power Ramp Pin. Connect a capacitor between RAMP and REF to provide a gradual linear power-up/down
ramp. See Detailed Description.

12 REF Reference Voltage for RAMP Capacitor. The reference is internally set to 1.9V.

13, 14,
17, 18,

SLUG

GND

GND Connection for the Power Stage. Solder the slug to the circuit board ground plane. Connect pins 13,
14, 17, and 18 to the slug with a straight board trace under the chip.

15 RFOUT

Power Amplifier Output. See Typical Operating Circuit for an example of a matching network, which pro­vides optimal output power at 836MHz. Connect to pin 16.

16 RFOUT Power Amplifier Output. Connect to pin 15.

19

SHDN

Shutdown Pin. Drive SHDN low to turn the device off. Drive above 2.0V to turn the device on. Drive V

SHDN

> 2.0V and V

GC

< 0.4V for standby mode.

20 GC

Gain-Control Pin. Apply VGCbetween 0.6V and 2.3V to control the output power with a monotonic dB/V
relationship. See the Typical Operating Characteristics for a typical relationship.

RISE TIME vs. RAMPING CAPACITANCE

1400

FULL POWER = +10dBm

1200

FULL POWER = +20dBm

1000

800

600

RISE TIME (µs)

400

200

0

0406020 80 100 120

FULL POWER = +30dBm

CAPACITANCE (nF)

MAX2235 toc10

MAX2235

+3.6V, 1W Autoramping Power
Amplifier for 900MHz Applications

6 _______________________________________________________________________________________

Detailed Description

The MAX2235 power amplifier (PA) operates over a
wide frequency range of 800MHz to 1000MHz. The sig­nal path consists of three stages: the input stage, the
driver stage, and the power stage. There are matching
circuits between the first and second stages, and
between the second and third stages. The bias circuits
process external commands to control the device’s
power-up/down and the gain of the PA.

Input Stage

The first stage is a variable-gain amplifier with 37dB
gain-control range. The input transistor acts as a
transconductor with constant bias current. Gain control
is achieved by steering the signal current from the input
transistor to the first output matching network (to drive
the second stage) or to a separate supply pin. This

stage operates in class A and remains on in standby
mode to ensure that the VSWR at the input does not
vary more than 1.5:1 compared with normal operation.
The input stage typically requires an external inductor
to achieve an optimum input VSWR.

Second Stage (Driver)

The driver produces a signal large enough to drive the
power stage into saturation. The driver stage operates
in Class C and is off during standby.

Second- and Third-Stage Matching

The interstage matching networks provide optimal load­ing and power transfer. The circuits are on-chip to save
board space. The bandwidths of the matching net­works allow the PA to operate over a wide frequency
range.

Typical Operating Circuit

100pF

1000pF

8.2nH

100pF

100pF

1

RFIN

2

GND

3

V

CC

4

V

MAX2235

CC

5

V

22pF

V

CC

CC

6

GND

7

GND

8

V

CC

9

V

CC

10

GND

SHDN

GND

GND

RFOUT

RFOUT

GND

GND

REF

RAMP

20

GC

19

18

17

16

15

14

13

12

11

1000pF

100pF

V

CC

0.01µF1µF

J1

SMA

V

CC

J3

J4

JU2

V

CC

3

2

JU1

1

V

CC

J2

SMA

*

0.068µF

470pF

47pF

1500pF

470pF

11pF

1000pF

1000pF

68pF

* VALUE OF OUTPUT INDUCTOR DEPENDS ON APPLICATION.

Third Stage (Power Stage)

This last stage delivers 30dBm to a 50Ω load. It oper­ates 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 VGCfrom 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
V

SHDN

> 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
ramping capacitor is determined from the Rise/Fall Time
vs. Ramping Capacitance curves in the Typical
Operating Characteristics.

Table 1. Operating Modes

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.

MAX2235

+3.6V, 1W Autoramping Power

Amplifier for 900MHz Applications

_______________________________________________________________________________________ 7

GC

SHDN

>2.0V >0.6V

MODE

On

Standby>2.0V <0.4V

Shutdown<0.5V Don’t care

Chip Information

TRANSISTOR COUNT: 668

MAX2235

+3.6V, 1W Autoramping Power
Amplifier for 900MHz Applications

Package Information

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

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© 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

TSSOP.EPS