_______________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 out-
put voltage ripple to 1mVp-p. With a well-filtered control
voltage (VCTRL), the MAX843/MAX844 also achieve less
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
____________________________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
MAX840/MAX843/MAX844
Low-Noise, Regulated, -2V GaAsFET Bias
________________________________________________________________
Maxim Integrated Products
1
( ) ARE FOR MAX843/MAX844
1
2
3
4
8
7
6
5
IN
GND
OUT
FB (CONT)
SHDN
NEGOUT
C1-
C1+
MAX840
MAX843
MAX844
SO
TOP VIEW
__________________Pin Configuration
MAX840
FB
OUT
SHDN
NEGOUT
C1-
C1+ IN
GND
VIN = 2.5V to 10.0V
(3 CELLS)
0.22µF
VOUT = -2.0V
(VGG of GaAsFET)
4.7µF
0.22µF
0.22µF
ON/OFF
__________Typical Operating Circuit
19-0388; Rev 1; 3/96
PART
MAX840C/D
MAX840ISA
MAX840ESA -40°C to +85°C
-25°C to +85°C
0°C to +70°C
TEMP. RANGE PIN-PACKAGE
Dice*
8 SO
8 SO
EVALUATION KIT MANUAL
FOLLOWS DATA SHEET
______________Ordering Information
* Dice are specified at TA= +25°C only.
MAX843C/D 0°C to +70°C Dice*
MAX843ISA -25°C to +85°C 8 SO
MAX843ESA -40°C to +85°C 8 SO
MAX844C/D 0°C to +70°C Dice*
MAX844ISA -25°C to +85°C 8 SO
MAX844ESA -40°C to +85°C 8 SO
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
MAX840/MAX843/MAX844
Low-Noise, Regulated, -2V GaAsFET Bias
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(Figures 2a and 2c, 2.5V ≤VIN ≤10V, VOUT = -2V, GND = 0V, RL= ∞, SHDN = VIN, TA= TMIN to TMAX, unless otherwise noted.
Typical values are measured at VIN = 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.
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.
Supply Voltage, VIN to GND..................................-0.3V to 10.5V
VNEGOUT to GND...................................................-10.5V to 0.3V
VIN to VNEGOUT.........................................................-0.3V to 21V
VOUT to GND (Note 1).......................................VNEGOUT to 0.3V
V SHDN to GND ............................................-0.3V to (VIN + 0.3V)
Continuous Power Dissipation (TA= +70°C)
SO (derate 5.88mW/°C above +70°C).........................471mW
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
C4 = 10µF
VIN = 3.6V,
RL= ∞or 500Ω
MAX844, VIN ≤3.6V, SHDN = 0V
MAX844, VIN = 10V, SHDN = 0V
MAX840/MAX843, VIN = 10V, SHDN = 0V
MAX843/MAX844, VCONT = 0V
MAX843/MAX844,
VCTRL = 2V
MAX840, VFB = 0V
MAX840, VFB = -0.5V
MAX840, no load
CONDITIONS
mVp-p1VOUT Ripple
mV/mA
28
V
OUT Load Regulation 38
µA
175 300
ISHUT
Shutdown Supply Current 940 1
nA±1 ±100ICONT
CONT Leakage Current nA±1 ±100IFB
FB Leakage Current V-0.516 -0.5 -0.484VFB
FB Voltage
-2.1 -2.0 -1.9
V2.5 10VIN
Supply Voltage Range
-0.5 to
(VIN - 0.6)
VOUT
Output Voltage Adjust Range
V
-2.05 -2.0 -1.95
VOUT
Output Voltage -2.1 -2.0 -1.9
-2.05 -2.0 -1.95
UNITSMIN TYP MAXSYMBOLPARAMETER
80 100 120
Oscillator Frequency FOSC VIN = 3.6V,
TA= +25°C 14 20 26 kHz
Input High Voltage VIH SHDN 2.2 V
VIN ≥2.7V,
IOUT = 0mA to 4mA
VIN ≥2.5V,
IOUT = 0mA to 3mA
VIN ≥2.5V,
IOUT = 0mA to 3mA
VIN ≥2.7V,
IOUT = 0mA to 4mA
V
MAX840, VFB = 0V
MAX843/MAX844,
VCTRL = 2V
Input Low Voltage VIL SHDN 0.35 V
Input Current IIN SHDN -1 1 µA
Input Capacitance CIN SHDN 10 pF
MAX840/MAX843/
MAX844
MAX844, SHDN = 0V
No load, VIN ≤3.6VIQ
Supply Current µA750 1300
MAX840/MAX843/MAX844
Low-Noise, Regulated, -2V GaAsFET Bias
_______________________________________________________________________________________
3
-2.040 010
OUTPUT VOLTAGE
vs. OUTPUT CURRENT
-2.050
MAX840-01
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
6
-2.070
-2.060
24 8
13579 -2.040
OUTPUT VOLTAGE vs. INPUT VOLTAGE
OVER TEMPERATURE
-2.050
-2.045
MAX840-02
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
-2.065
-2.060
-2.055
10624 83579
T
A
= +85°C
TA = +25°C
TA = -40°C
20
010
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
60
40
MAX840-03
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
6
120
100
80
24 83579
V
OUT < -1.95V
(CIRCUIT OF FIG 2a)
VOUT < -1.95V
(CIRCUIT OF FIG 2d)
VOUT < 2mVp-p RIPPLE
(CIRCUIT OF FIG 2d)
VOUT < 2mVp-p RIPPLE
(CIRCUIT OF FIG 2a)
High-current operation not
recommended for extended
periods of time.
010
N0-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
2
1
MAX840-05
INPUT VOLTAGE (V)
NO-LOAD SUPPLY CURRENT (mA)
6
5
4
3
24 83579
010
NEGOUT CURRENT vs. INPUT VOLTAGE
10
5
MAX840-04
INPUT VOLTAGE (V)
NEGOUT CURRENT (mA)
6
30
25
20
15
24 83579
V
NEGOUT = 0.9 x VNEGOUT(NO LOAD)
SHUTDOWN
(MAX844)
0
SUPPLY CURRENT vs. TEMPERATURE
3
2
1
MAX840-06
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
40
7
6
5
4
-40 0 80-20 20 60 100
VIN = 10V
VIN = 3.6V
0.4
START-UP TIME vs. INPUT VOLTAGE
1.6
1.2
0.8
MAX840-07
INPUT VOLTAGE (V)
START-UP TIME (ms)
6
2.8
2.4
2.0
24 8357910
__________________________________________Typical Operating Characteristics
(Circuit of Figure 2a, VIN = 3.6V, TA= +25°C, unless otherwise noted.)
MAX840/MAX843/MAX844
Low-Noise, Regulated, -2V GaAsFET Bias
4 _______________________________________________________________________________________
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2a, VIN = 3.6V, TA= +25°C, unless otherwise noted.)
MAX840 OUTPUT NOISE AND RIPPLE
(C1 = C2 = C3 = 1µF, C4 = 10µF)
VIN = 3.6V, VOUT = -2V, IOUT = 4mA, AC COUPLED
10µs/div
VOUT
500µV/div
MAX840 OUTPUT NOISE AND RIPPLE
(C1 = C2 = C3 = 0.22µF, C4 = 4.7µF)
VIN = 3.6V, VOUT = -2V, IOUT = 4mA, AC COUPLED
10µs/div
VOUT
1mV/div
MAX843/MAX844 OUTPUT NOISE AND RIPPLE
(C1 = C2 = C3 = 1µF, C4 = 10µF)
VIN = 3.6V, VOUT = -2V, IOUT = 4mA, AC COUPLED
10µs/div
VOUT
500µV/div
MAX843/MAX844 OUTPUT NOISE AND RIPPLE
(C1 = C2 = C3 = 0.22µF, C4 = 4.7µF)
VIN = 3.6V, VOUT = -2V, IOUT = 4mA, AC COUPLED
10µs/div
VOUT
1mV/div
70 10
OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
90
80
MAX840-17
SUPPLY VOLTAGE (V)
OSCILLATOR FREQUENCY (kHz)
6
150
140
120
130
110
100
24 83579
T
A
= +25°C, +85°C
TA = -40°C
SHDN = HIGH
15 10
MAX844
OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE
19
17
MAX840-18
SUPPLY VOLTAGE (V)
OSCILLATOR FREQUENCY (kHz)
6
31
29
25
27
23
21
24 83579
T
A
= +25°C, +85°C
TA = -40°C
SHDN = LOW
MAX840/MAX843/MAX844
Low-Noise, Regulated, -2V GaAsFET Bias
_______________________________________________________________________________________
5
MAX840 NOISE SPECTRUM
(C1 = C2 = C3 = 0.22µF, C4 = 4.7µF)
50
00.1 1 10 100 1000
10
FREQUENCY (kHz)
NOISE (dBµV)
20
30
40
VIN = 3.6V,
IOUT = 4mA
MAX843/MAX844 NOISE SPECTRUM
(C1 = C2 = C3 = 1µF, C4 = 10µF)
40
-10 0.1 1 10 100 1000
0
FREQUENCY (kHz)
NOISE (dBµV)
10
20
30
VIN = 3.6V,
IOUT = 4mA
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2a, VIN = 3.6V, TA= +25°C, unless otherwise noted.)
MAX840 NOISE SPECTRUM
(C1 = C2 = C3 = 1µF, C4 = 10µF)
40
-10 0.1 1 10 100 1000
0
FREQUENCY (kHz)
NOISE (dBµV)
10
20
30
VIN = 3.6V,
IOUT = 4mA
VOUT
NOTE: dBµV = 20 LOG ______
1µV
MAX840/MAX843/MAX844
Low-Noise, Regulated, -2V GaAsFET Bias
6 _______________________________________________________________________________________
START-UP FROM SHUTDOWN
VIN = 3.6V, VOUT = -2V, IOUT = 4mA
500µs/div
VOUT
1V/div
0V
0V
VSHDN
2V/div
LINE-TRANSIENT RESPONSE
VOUT = -2V, IOUT = 4mA, AC COUPLED
5ms/div
VOUT
10mV/div
VIN
2.7V
3.3V
LOAD-TRANSIENT RESPONSE
VIN = 3.6V, VOUT = -2V 5ms/div
VOUT
20mV/div
0.01mA IOUT
4mA
____________________________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)
50
00.1 1 10 100 1000
10
FREQUENCY (kHz)
NOISE (dBµV)
20
30
40
VIN = 3.6V,
IOUT = 4mA
VOUT
NOTE: dBµV = 20 LOG ______
1µV
MAX840/MAX843/MAX844
Low-Noise, Regulated, -2V GaAsFET Bias
_______________________________________________________________________________________ 7
______________________________________________________________Pin Description
Dual Mode is a trademark of Maxim Integrated Products.
MAX843
MAX844
1
2
3
—
4
8
7
6
5
MAX840 NAME FUNCTION
1 C1+ Positive Terminal for C1
PIN
2 C1- Negative Terminal for C1
3 NEGOUT Negative Output Voltage (unregulated)
5 FB 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).
4 SHDN Active-Low, TTL Logic-Level Shutdown Input
8 IN Positive Power-Supply Input
7 GND Ground
6 OUT Regulated Negative Output Voltage
— CONT Control Voltage Input. To set VOUT, connect a resistor divider between OUT and a
positive control voltage between 0V and 10V (Figure 2c).
MAX840
-0.5V
REF
CHARGE
PUMP
IN
N
C1+
C1-
NEGOUT
SHDN
OUT
CONNECT TO
GND TO SET
VOUT = -2V
FB
GND
MAX843
MAX844
CHARGE
PUMP
IN
N
C1+
C1-
NEGOUT
SHDN
OUT
CONTROL
VOLTAGE
CONT
GND
R2
R1
Figure 1a. MAX840 Block Diagram Figure 1b. MAX843/MAX844 Block Diagram
MAX840/MAX843/MAX844
Low-Noise, Regulated, -2V GaAsFET Bias
8 _______________________________________________________________________________________
_______________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 neg-
ative 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 VOUT. In addition, the linear regu-
lator’s excellent AC rejection attenuates noise from the
incoming supply.
__________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 volt-
age by connecting FB to the midpoint of a resistor
voltage divider from OUT to GND (Figure 2b). VIN
must be 0.6V above the absolute value of VOUT to
allow proper regulation. The output voltage is calculat-
ed from the formula below. Choose R2 to be between
100kΩand 400kΩ.
VOUT = (-0.5V)(1 + R2 / R1)
For the MAX843/MAX844, set the output voltage by
connecting a resistor voltage divider between OUT and
a positive control voltage (VCTRL) (Figure 2c).
VOUT = -VCTRL (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 dis-
abled. When the MAX844 is in shutdown, only the lin-
ear regulator is disabled and the NEGOUT output
remains enabled. However, the charge-pump oscilla-
tion 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 shut-
down.
Capacitors
Use capacitors with low effective series resistance
(ESR) to maintain a low dropout voltage (VIN - |VOUT|).
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 approxi-
mately: ROUT = RO+ 4 x ESRC1 + ESRC4 +
1 / (fSx C1) + R(linear regulator)
where [RO+ R(linear regulator)], the effective resistance
of the internal switches and the resistance across the
linear regulator, is approximately 71Ωat VIN = 2.5V,
48Ωat VIN = 5V, and 40Ωat VIN = 10V.
C1, C2, and C3 should be 1µF capacitors with less than
0.8ΩESR. C4 should be a 10µF capacitor with less
than 0.2ΩESR. 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 tanta-
lum or ceramic types. External capacitor values can be
adjusted to optimize size and cost.
Layout and Grounding
Good layout is important, primarily for good noise perfor-
mance. 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.
MAX840/MAX843/MAX844
Low-Noise, Regulated, -2V GaAsFET Bias
_______________________________________________________________________________________ 9
MAX840
FB
OUT
SHDN
NEGOUT
C1-
C1+ IN
GND
VIN
C3
1µF
VOUT = -2V
(VGG of GaAsFET)
C4
10µF
C1
1µF
C2
1µF
1
ON/OFF
2
3
45
6
8
7
MAX840
FB
OUT
SHDN
NEGOUT
C1-
C1+ IN
GND
VIN
C3
1µF
VOUT = (-0.5V) 1+ R2
R1
C4
10µF
C1
1µF
C2
1µFR2
100k
R1
100k
( )
1
2
3
45
6
8
7
ON/OFF
MAX843
MAX844
CONT
OUT
SHDN
NEGOUT
C1-
C1+ IN
GND
VIN
C3
1µF
VOUT = -0.5V to -9.4V @ 4mA
C4
10µF
C1
1µF
C2
1µFR2
100k
R1
100k
VCTRL (0V TO 10V)
1
2
3
45
6
8
7
ON/OFF
MAX840
FB
OUT
SHDN
NEGOUT
C1-
C1+ IN
GND
VIN
C3
0.22µF
VOUT = -2V
(VGG of GaAsFET)
C4
4.7µF
C1
0.22µF
C2
0.22µF
1
2
3
45
6
8
7
ON/OFF
Figure 2a. MAX840 Standard Application Circuit Figure 2b. MAX840 Adjustable Configuration
Figure 2d. MAX840 Application Circuit Using Smaller Capacitors
Figure 2c. MAX843/MAX844 Standard Application Circuit
MAX840/MAX843/MAX844
Low-Noise, Regulated, -2V GaAsFET Bias
10 ______________________________________________________________________________________
( ) ARE FOR MAX843/MAX844
TRANSISTOR COUNT: 148
SUBSTRATE CONNECTED TO IN
___________________Chip Topography
IN
NEGOUT
NEGOUT
SHDN
0.145"
(3.683mm)
0.085"
(2.159mm)
FB (CONT)
GND
GND
OUT
C1-
C1+
