Rainbow Electronics MAX844 User Manual

19-0388; Rev 1; 3/96

EVALUATION KIT MANUAL

FOLLOWS DATA SHEET

Low-Noise, Regulated, -2V GaAsFET Bias

_______________General Description

The MAX840/MAX843/MAX844 low-noise, inverting charge-pump power supplies are ideal for biasing GaAsFETs in cellular telephone transmitter amplifiers. They operate with inputs down to 2.5V.

The MAX840 offers both a -2V preset output and a -0.5V to -9.4V adjustable output. The MAX843/MAX844 use an external positive control voltage to set the negative output voltage. Input voltage range for all the devices is

2.5V to 10V, and output current is 4mA with VIN> 2.7V. These circuits can operate with small capacitors, as low as 0.22µF.

An internal linear regulator reduces the MAX840’s output voltage ripple to 1mVp-p. With a well-filtered control voltage (V

), the MAX843/MAX844 also achieve less

CTRL

than 1mVp-p typical output ripple. Supply current is 750µA, and reduces to less than 1µA in shutdown (MAX840/MAX843). The MAX844’s unregulated output is active in shutdown, with the charge pump switching at 20kHz. It provides a low-power LCD supply.

________________________Applications

Cellular Phones GaAsFET Power Amplifier Modules Personal Communicators, PDAs Wireless Data Loggers Continuously Adjustable GaAsFET Bias LCD-Bias Contrast Control Regulated Negative Power Supplies

__________Typical Operating Circuit

VIN = 2.5V to 10.0V

(3 CELLS)

____________________________Features

♦ Fixed -2V or Adjustable -0.5V to -9.4V Output

at 4mA (MAX840)

♦ 2.5V to 10V Input Voltage Range ♦ Operate with Small Capacitors (as low as 0.22µF) ♦ 1mVp-p Output Voltage Ripple ♦ Charge-Pump Switching Frequency:

100kHz in Normal Operation 20kHz in Shutdown Mode (MAX844)

♦ 1µA Max Logic-Level Shutdown Over Temp.

(MAX840/MAX843)

♦ Small 8-Pin SO Package

______________Ordering Information

PART

MAX840C/D

MAX840ISA MAX840ESA -40°C to +85°C MAX843C/D MAX843ISA -25°C to +85°C 8 SO MAX843ESA -40°C to +85°C 8 SO MAX844C/D MAX844ISA -25°C to +85°C 8 SO MAX844ESA -40°C to +85°C 8 SO

* Dice are specified at TA= +25°C only.

TEMP. RANGE PIN-PACKAGE

0°C to +70°C

-25°C to +85°C

0°C to +70°C Dice*

Dice* 8 SO 8 SO

MAX840/MAX843/MAX844

__________________Pin Configuration

TOP VIEW

C1+

C1-

NEGOUT

SHDN

( ) ARE FOR MAX843/MAX844

MAX840 MAX843 MAX844

Maxim Integrated Products

8 7 6 5

IN GND OUT

FB (CONT)

0.22µF

ON/OFF

0.22µF

C1+

C1-

NEGOUT

SHDN 

________________________________________________________________

MAX840

GND

OUT

= -2.0V

OUT

of GaAsFET)

4.7µF

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800

Low-Noise, Regulated, -2V GaAsFET Bias

ABSOLUTE MAXIMUM RATINGS

Supply Voltage, V V

NEGOUT

OUT

SHDN

to GND...................................................-10.5V to 0.3V

to V

NEGOUT

to GND (Note 1).......................................V

to GND ............................................-0.3V to (VIN+ 0.3V)

Continuous Power Dissipation (T

to GND ..................................-0.3V to 10.5V

.........................................................-0.3V to 21V

to 0.3V

= +70°C)

NEGOUT

SO (derate 5.88mW/°C above +70°C).........................471mW

Note 1: The output may be shorted to NEGOUT or GND if the package power dissipation is not exceeded. Typical short-circuit

current from 4V to GND is 40mA.

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.

ELECTRICAL CHARACTERISTICS

(Figures 2a and 2c, 2.5V ≤ VIN≤ 10V, V Typical values are measured at VIN= 3.6V and TA= +25°C.)

Supply Voltage Range

Output Voltage

MAX840/MAX843/MAX844

Output Voltage Adjust Range

FB Voltage FB Leakage Current CONT Leakage Current

CONT

Supply Current µA750 1300

Shutdown Supply Current

Load Regulation

OUT

Ripple

OUT

SHUT

Oscillator Frequency F

Input High Voltage V Input Low Voltage V Input Current I Input Capacitance C

= -2V, GND = 0V, RL= ∞, SHDN = VIN, TA= T

OUT

MAX840, VFB= 0V

OUT

MAX843/MAX844, V

= 2V

CTRL

OUT

MAX840, no load

MAX840, VFB= -0.5V MAX843/MAX844, V No load, VIN≤ 3.6VI

MAX840/MAX843, VIN= 10V, SHDN = 0V MAX844, VIN= 10V, SHDN = 0V MAX844, VIN≤ 3.6V, SHDN = 0V

VIN= 3.6V, RL= ∞ or 500Ω

C4 = 10µF

OSC

VIN= 3.6V, TA= +25°C

SHDN 2.2 V

SHDN 0.35 V

SHDN -1 1 µA

SHDN 10 pF

Operating Temperature Ranges

MAX84_I_ _A ...................................................-25°C to +85°C

MAX84_E_ _A ..................................................-40°C to +85°C

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

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

to T

MIN

, unless otherwise noted.

MAX

CONDITIONS

VIN≥ 2.5V,

= 0mA to 3mA

OUT

VIN≥ 2.7V,

= 0mA to 4mA

OUT

VIN≥ 2.5V,

= 0mA to 3mA

OUT

VIN≥ 2.7V,

= 0mA to 4mA

OUT

-2.1 -2.0 -1.9

-2.05 -2.0 -1.95

-0.5 to

- 0.6)

= 0V

CONT

1 940 175 300

MAX840, VFB= 0V MAX843/MAX844,

= 2V

CTRL

MAX840/MAX843/ MAX844

MAX844, SHDN = 0V

80 100 120 14 20 26

38 28

UNITSMIN TYP MAXSYMBOLPARAMETER

mV/mA

mVp-p1V

V2.5 10V

V-0.516 -0.5 -0.484V nA±1 ±100I nA±1 ±100I

µA

kHz

2 _______________________________________________________________________________________

Low-Noise, Regulated, -2V GaAsFET Bias

__________________________________________Typical Operating Characteristics

(Circuit of Figure 2a, VIN= 3.6V, TA= +25°C, unless otherwise noted.)

OUTPUT VOLTAGE 

vs. OUTPUT CURRENT

-2.070

MAX840-01

-2.060

-2.050

OUTPUT VOLTAGE (V)

-2.040 010

24 8

13579

OUTPUT CURRENT (mA)

MAXIMUM OUTPUT CURRENT 

vs. INPUT VOLTAGE

120

100

(CIRCUIT OF FIG 2d)

(CIRCUIT OF FIG 2a)

< -1.95V

OUT

< -1.95V

OUT

MAX840-03

High-current operation not recommended for extended periods of time.

OUTPUT VOLTAGE vs. INPUT VOLTAGE

OVER TEMPERATURE

-2.065

-2.060

-2.055 T

= +85°C

-2.050

OUTPUT VOLTAGE (V)

-2.045

-2.040

TA = +25°C

TA = -40°C

INPUT VOLTAGE (V)

NEGOUT CURRENT vs. INPUT VOLTAGE

= 0.9 x V

NEGOUT

NEGOUT(NO LOAD)

MAX840-02

10624 83579

MAX840-04

MAX840/MAX843/MAX844

MAXIMUM OUTPUT CURRENT (mA)

24 83579

INPUT VOLTAGE (V)

N0-LOAD SUPPLY CURRENT

vs. INPUT VOLTAGE

NO-LOAD SUPPLY CURRENT (mA)

24 83579

INPUT VOLTAGE (V)

_______________________________________________________________________________________

< 2mVp-p RIPPLE

OUT

(CIRCUIT OF FIG 2a)

< 2mVp-p RIPPLE

OUT

(CIRCUIT OF FIG 2d)

NEGOUT CURRENT (mA)

24 83579

INPUT VOLTAGE (V)

SUPPLY CURRENT vs. TEMPERATURE

MAX840-05

SUPPLY CURRENT (mA)

VIN = 10V

VIN = 3.6V

-40 0 80-20 20 60 100 TEMPERATURE (°C)

MAX840-06

START-UP TIME (ms)

SHUTDOWN

(MAX844)

START-UP TIME vs. INPUT VOLTAGE

2.8

2.4

2.0

1.6

1.2

0.8

0.4 24 8357910

INPUT VOLTAGE (V)

MAX840-07

Low-Noise, Regulated, -2V GaAsFET Bias

____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 2a, VIN= 3.6V, TA= +25°C, unless otherwise noted.)

OSCILLATOR FREQUENCY 

vs. SUPPLY VOLTAGE

150 140 130 120 110 100

OSCILLATOR FREQUENCY (kHz)

80 70

24 83579

SUPPLY VOLTAGE (V)



= +25°C, +85°C

MAX840-17

TA = -40°C

SHDN = HIGH

MAX840 OUTPUT NOISE AND RIPPLE

(C1 = C2 = C3 = 1µF, C4 = 10µF)

MAX840/MAX843/MAX844



OUT

500µV/div

OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE

MAX844

31 29 27 25 23 21 19

OSCILLATOR FREQUENCY (kHz)

17 15

24 83579



= +25°C, +85°C

TA = -40°C

SHDN = LOW

SUPPLY VOLTAGE (V)

MAX840 OUTPUT NOISE AND RIPPLE (C1 = C2 = C3 = 0.22µF, C4 = 4.7µF)

MAX840-18



OUT

1mV/div



10µs/div

VIN = 3.6V, V

OUT

= -2V, I

= 4mA, AC COUPLED

OUT

MAX843/MAX844 OUTPUT NOISE AND RIPPLE

(C1 = C2 = C3 = 1µF, C4 = 10µF)



10µs/div

VIN = 3.6V, V

OUT

= -2V, I

= 4mA, AC COUPLED

OUT



OUT

500µV/div

VIN = 3.6V, V

OUT

MAX843/MAX844 OUTPUT NOISE AND RIPPLE

(C1 = C2 = C3 = 0.22µF, C4 = 4.7µF)

VIN = 3.6V, V

OUT

= -2V, I



10µs/div

= 4mA, AC COUPLED

OUT



10µs/div

= 4mA, AC COUPLED

OUT

4 _______________________________________________________________________________________



OUT

1mV/div

Low-Noise, Regulated, -2V GaAsFET Bias

____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 2a, VIN= 3.6V, TA= +25°C, unless otherwise noted.)

MAX840 NOISE SPECTRUM

VIN = 3.6V, I

OUT

NOISE (dBµV)

-10

0.1 1

VIN = 3.6V, I

OUT

= 4mA

(C1 = C2 = C3 = 1µF, C4 = 10µF)

10 100 1000

FREQUENCY (kHz)

MAX840 NOISE SPECTRUM

(C1 = C2 = C3 = 0.22µF, C4 = 4.7µF)

MAX840/MAX843/MAX844

NOTE: dBµV = 20 LOG

OUT

______

1µV

NOISE (dBµV)

0.1 1

VIN = 3.6V, I

OUT

NOISE (dBµV)

-10

0.1 1

10 100 1000

FREQUENCY (kHz)

MAX843/MAX844 NOISE SPECTRUM

(C1 = C2 = C3 = 1µF, C4 = 10µF)

= 4mA

10 100 1000

FREQUENCY (kHz)

_______________________________________________________________________________________

Low-Noise, Regulated, -2V GaAsFET Bias

____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 2a, VIN= 3.6V, TA= +25°C, unless otherwise noted.)

MAX843/MAX844 NOISE SPECTRUM

(C1 = C2 = C3 = 0.22µF, C4 = 4.7µF)

VIN = 3.6V,

= 4mA

OUT

NOISE (dBµV)

NOTE: dBµV = 20 LOG

OUT

______

1µV

0.1 1 FREQUENCY (kHz)

START-UP FROM SHUTDOWN

MAX840/MAX843/MAX844

500µs/div

VIN = 3.6V, V



LOAD-TRANSIENT RESPONSE

= -2V, I

OUT



OUT

20mV/div

OUT

10 100 1000



OUT

1V/div

SHDN

2V/div

= 4mA

LINE-TRANSIENT RESPONSE



OUT

10mV/div

0.01mA I

OUT

4mA

5ms/div

= 4mA, AC COUPLED

VIN = 3.6V, V

OUT

= -2V

5ms/div

OUT

= -2V, I

OUT

6 _______________________________________________________________________________________

3.3V

2.7V

Low-Noise, Regulated, -2V GaAsFET Bias

______________________________________________________________Pin Description

MAX840

1 C1+ Positive Terminal for C1 2 C1- Negative Terminal for C1 3 NEGOUT Negative Output Voltage (unregulated) 4 SHDN Active-Low, TTL Logic-Level Shutdown Input

5 FB

— CONT

6 OUT Regulated Negative Output Voltage 7 GND Ground 8 IN Positive Power-Supply Input

Dual Mode is a trademark of Maxim Integrated Products.

MAX843 MAX844

1 2 3 4

—

6 7 8

NAME FUNCTION

Dual Mode™ Feedback Input. When FB is grounded, the output is preset to -2V. To select other output voltages, connect FB to an external resistor divider (Figure 2b).

Control Voltage Input. To set V

, connect a resistor divider between OUT and a

OUT

positive control voltage between 0V and 10V (Figure 2c).

MAX840/MAX843/MAX844

C1+

CHARGE

-0.5V REF

PUMP

C1-

NEGOUT

SHDN

Figure 1a. MAX840 Block Diagram

_______________________________________________________________________________________ 7

MAX840

GND

OUT

CONNECT TO  GND TO SET V

= -2V

OUT

C1+

CHARGE

C1-

PUMP

MAX843 MAX844

GND

SHDN

NEGOUT



Figure 1b. MAX843/MAX844 Block Diagram

OUT

CONT

CONTROL VOLTAGE

Low-Noise, Regulated, -2V GaAsFET Bias

_______________Detailed Description

The MAX840/MAX843/MAX844 are low-noise, inverting, regulated charge-pump power supplies designed for biasing GaAsFET devices, such as power-amplifier modules in cellular handsets.

The applied input voltage (VIN) is first inverted to a negative voltage at NEGOUT by a capacitive charge pump. This voltage is then regulated by an internal low-noise linear regulator, and appears at OUT (Figure 1). The minimum (most negative) output voltage achievable is the inverted positive voltage, plus the 0.6V required by the post-regulator. For the MAX840, the linear regulator reduces ripple noise induced by the charge-pump inverter to 1mVp-p at V lator’s excellent AC rejection attenuates noise from the incoming supply.

. In addition, the linear regu-

OUT

__________Applications Information

Setting the Output Voltage

For the MAX840, select either a fixed or adjustable output voltage. Connect FB directly to GND for a fixed

-2V output (Figure 2a). Select an alternate output voltage by connecting FB to the midpoint of a resistor voltage divider from OUT to GND (Figure 2b). V

MAX840/MAX843/MAX844

must be 0.6V above the absolute value of V allow proper regulation. The output voltage is calculated from the formula below. Choose R2 to be between 100kΩ and 400kΩ.

= (-0.5V)(1 + R2 / R1)

OUT

For the MAX843/MAX844, set the output voltage by connecting a resistor voltage divider between OUT and a positive control voltage (V

= -V

OUT

CTRL

) (Figure 2c).

CTRL

(R2 / R1)

Shutdown Mode

The MAX840/MAX843/MAX844 feature a shutdown mode that reduces the supply current to 1µA max over temperature (300µA max for the MAX844). When the MAX840/MAX843 are in shutdown, the outputs (OUT, NEGOUT) and the charge-pump oscillator are disabled. When the MAX844 is in shutdown, only the linear regulator is disabled and the NEGOUT output remains enabled. However, the charge-pump oscillation frequency is reduced to 20kHz, reducing the available power at NEGOUT. The output voltage at NEGOUT can be used to bias an LCD while in shutdown.

OUT

Capacitors

Use capacitors with low effective series resistance (ESR) to maintain a low dropout voltage (VIN- |V The overall dropout voltage is a function of the charge pump’s output resistance and the voltage drop across the linear regulator (N-channel pass transistor). At the 100kHz switching frequency, the charge-pump output resistance is a function of C1 and C2’s ESR. Therefore, minimizing the ESR of the charge-pump capacitors minimizes the dropout voltage.

The output resistance of the entire circuit is approximately:

= RO+ 4 x ESRC1+ ESRC4+

OUT

1 / (fSx C1) + R

where [RO+ R of the internal switches and the resistance across the linear regulator, is approximately 71Ω at VIN= 2.5V, 48Ω at VIN= 5V, and 40Ω at VIN= 10V.

C1, C2, and C3 should be 1µF capacitors with less than

0.8Ω ESR. C4 should be a 10µF capacitor with less than 0.2Ω ESR. Smaller capacitor values can be used (C1 = C2 = C3 = 0.22µF, C4 = 4.7µF) with a small increase in output noise and ripple (Figure 2d). All capacitors should be either surface-mount chip tantalum or ceramic types. External capacitor values can be adjusted to optimize size and cost.

(linear regulator)

], the effective resistance

OUT

Layout and Grounding

Good layout is important, primarily for good noise performance. Take the following steps to ensure good layout:

1) Mount all components as close together as possible.

2) Keep traces short to minimize parasitic inductance and capacitance. This includes connections to FB.

3) Use a ground plane.

Noise and Ripple Measurement

Accurately measuring the output noise and ripple is a challenge. Slight momentary differences in ground potential between the MAX840/MAX843/MAX844 circuit and the oscilloscope (which results from the charge pump’s switching action) cause ground currents in the probe’s wires, inducing sharp voltage spikes. For best results, measure directly across the output capacitor (C4). Do not use the ground lead of the oscilloscope probe; instead, remove the probe’s tip cover and touch the ground ring on the probe directly to C4’s ground terminal. You can also use a Tektronix chassis-mount test jack (part no. 131-0258) to connect your scope probe directly. This direct connection gives the most accurate noise and ripple measurement.

8 _______________________________________________________________________________________

Low-Noise, Regulated, -2V GaAsFET Bias

MAX840/MAX843/MAX844

C1

1µF

C2

1µF

ON/OFF

C1+

C1-

NEGOUT

SHDN

MAX840

GND

OUT

C3 1µF

= -2V

OUT

of GaAsFET)

C4 10µF

C1

1µF

C2

1µF

ON/OFF

C1+

C1-

NEGOUT

SHDN

MAX840

GND

= (-0.5V) 1+

OUT

R2 100k

R1

100k

Figure 2a. MAX840 Standard Application Circuit Figure 2b. MAX840 Adjustable Configuration

C1

1µF

C2

1µF

ON/OFF

C1+

C1-

NEGOUT

SHDN

OUT

MAX843 MAX844

OUT

CONT

GND

(0V TO 10V)

CTRL

= -0.5V to -9.4V @ 4mA

R2 100k

R1 100k

C3 1µF

C4 10µF

0.22µF

ON/OFF

C1

C2

C1+

C1-

NEGOUT

SHDN

MAX840



GND

OUT

C3

0.22µF

OUT

of GaAsFET)

C4

4.7µF

C3 1µF

R2

( )

C4 10µF

= -2V

Figure 2c. MAX843/MAX844 Standard Application Circuit

_______________________________________________________________________________________ 9

Figure 2d. MAX840 Application Circuit Using Smaller Capacitors

Low-Noise, Regulated, -2V GaAsFET Bias

___________________Chip Topography

C1+

GND GND

NEGOUT

C1-

0.145"

(3.683mm)

MAX840/MAX843/MAX844

SHDN

0.085"

(2.159mm)

FB (CONT)

OUT

( ) ARE FOR MAX843/MAX844 TRANSISTOR COUNT: 148

SUBSTRATE CONNECTED TO IN

10 ______________________________________________________________________________________

Rainbow Electronics MAX844 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual