19-0388; Rev 1; 3/96
UAL
IT MAN
TION K
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ET
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L
H
A
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TA
WS DA
FOLLO
Low-Noise, Regulated, -2V GaAsFET Bias
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 (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
__________Typical Operating Circuit
____________________________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
TEMP. RANGE
PIN-PACKAGE
MAX840C/D
0°C to +70°C
Dice*
MAX840ISA
MAX840ESA
MAX843C/D
MAX843ISA
MAX843ESA
MAX844C/D
MAX844ISA
MAX844ESA
-25°C to +85°C
-40°C to +85°C
0°C to +70°C
-25°C to +85°C
-40°C to +85°C
0°C to +70°C
-25°C to +85°C
-40°C to +85°C
8 SO
8 SO
Dice*
8 SO
8 SO
Dice*
8 SO
8 SO
* Dice are specified at TA = +25°C only.
VIN = 2.5V to 10.0V
(3 CELLS)
0.22µF
__________________Pin Configuration
IN
C1+
0.22µF
C1-
MAX840
VOUT = -2.0V
(VGG of GaAsFET)
TOP VIEW
OUT
4.7µF
NEGOUT
C1+ 1
8
IN
C1- 2
7
GND
6
OUT
5
FB (CONT)
0.22µF
NEGOUT 3
SHDN 4
ON/OFF
MAX840
MAX843
MAX844
FB
SHDN
SO
GND
( ) ARE FOR MAX843/MAX844
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
MAX840/MAX843/MAX844
_______________General Description
MAX840/MAX843/MAX844
Low-Noise, Regulated, -2V GaAsFET Bias
ABSOLUTE MAXIMUM RATINGS
Operating Temperature Ranges
Supply Voltage, VIN to GND ..................................-0.3V to 10.5V
VNEGOUT to GND ...................................................-10.5V to 0.3V
MAX84_I_ _A ...................................................-25°C to +85°C
VIN to VNEGOUT.........................................................-0.3V to 21V
MAX84_E_ _A ..................................................-40°C to +85°C
VOUT to GND (Note 1).......................................VNEGOUT to 0.3V
Storage Temperature Range .............................-65°C to +150°C
V SHDN to GND ............................................-0.3V to (VIN + 0.3V)
Lead Temperature (soldering, 10sec) .............................+300°C
Continuous Power Dissipation (TA = +70°C)
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, 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.)
PARAMETER
Supply Voltage Range
SYMBOL
CONDITIONS
VIN
VOUT
MAX843/MAX844,
VCTRL = 2V
Output Voltage Adjust Range
VFB
MAX840, no load
IFB
MAX840, VFB = -0.5V
ICONT
IQ
ISHUT
-2.0
-1.9
VIN ≥ 2.7V,
IOUT = 0mA to 4mA
-2.1
-2.0
-1.9
VIN ≥ 2.5V,
IOUT = 0mA to 3mA
-2.05
-2.0
-1.95
VIN ≥ 2.7V,
IOUT = 0mA to 4mA
-2.05
-2.0
-1.95
V
-0.516
-0.484
V
±1
±100
nA
MAX843/MAX844, VCONT = 0V
±1
±100
nA
No load, VIN ≤ 3.6V
750
1300
µA
940
MAX844, VIN ≤ 3.6V, SHDN = 0V
VOUT Ripple
C4 = 10µF
VIN = 3.6V,
TA = +25°C
Input High Voltage
VIH
SHDN
Input Low Voltage
VIL
SHDN
Input Current
IIN
SHDN
Input Capacitance
CIN
SHDN
2
1
MAX844, VIN = 10V, SHDN = 0V
VIN = 3.6V,
RL = ∞ or 500Ω
FOSC
V
-0.5
VOUT Load Regulation
Oscillator Frequency
V
-2.1
MAX840/MAX843, VIN = 10V, SHDN = 0V
Shutdown Supply Current
UNITS
10
-0.5 to
(VIN - 0.6)
FB Leakage Current
Supply Current
MAX
VIN ≥ 2.5V,
IOUT = 0mA to 3mA
VOUT
FB Voltage
CONT Leakage Current
TYP
2.5
MAX840, VFB = 0V
Output Voltage
MIN
µA
175
300
MAX840, VFB = 0V
3
8
MAX843/MAX844,
VCTRL = 2V
2
8
1
MAX840/MAX843/
MAX844
MAX844, SHDN = 0V
mV/mA
mVp-p
80
100
120
14
20
26
2.2
kHz
V
-1
10
_______________________________________________________________________________________
0.35
V
1
µA
pF
Low-Noise, Regulated, -2V GaAsFET Bias
OUTPUT VOLTAGE
vs. OUTPUT CURRENT
OUTPUT VOLTAGE vs. INPUT VOLTAGE
OVER TEMPERATURE
MAX840-02
-2.065
MAX840-01
-2.070
OUTPUT VOLTAGE (V)
-2.050
-2.055
TA = +85°C
-2.050
TA = +25°C
TA = -40°C
-2.045
-2.040
-2.040
0
1
2
3
4
5
6
8
7
9
10
2
3
4
OUTPUT CURRENT (mA)
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
NEGOUT CURRENT (mA)
High-current operation not
recommended for extended
periods of time.
40
VOUT < 2mVp-p RIPPLE
(CIRCUIT OF FIG 2a)
VOUT < 2mVp-p RIPPLE
(CIRCUIT OF FIG 2d)
20
10
20
15
10
SHUTDOWN
(MAX844)
5
0
3
4
5
6
7
8
9
10
2
3
4
INPUT VOLTAGE (V)
N0-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
6
2
2.4
5
VIN = 10V
4
3
2
1
0
INPUT VOLTAGE (V)
9
10
1.6
1.2
0.4
0
8
2.0
0.8
VIN = 3.6V
1
7
10
9
START-UP TIME vs. INPUT VOLTAGE
START-UP TIME (ms)
SUPPLY CURRENT (mA)
3
6
8
2.8
MAX840-06
7
MAX840-05
4
5
7
SUPPLY CURRENT vs. TEMPERATURE
5
4
6
5
INPUT VOLTAGE (V)
MAX840-07
2
NO-LOAD SUPPLY CURRENT (mA)
9
VNEGOUT = 0.9 x VNEGOUT(NO LOAD)
VOUT < -1.95V
(CIRCUIT OF FIG 2d)
60
3
8
25
0
2
7
30
MAX840-03
MAXIMUM OUTPUT CURRENT (mA)
VOUT < -1.95V
(CIRCUIT OF FIG 2a)
80
6
NEGOUT CURRENT vs. INPUT VOLTAGE
120
100
5
INPUT VOLTAGE (V)
MAX840-04
OUTPUT VOLTAGE (V)
-2.060
-2.060
-40
-20
0
20
40
60
TEMPERATURE (°C)
80
100
2
3
4
5
6
7
8
9
10
INPUT VOLTAGE (V)
_______________________________________________________________________________________
3
MAX840/MAX843/MAX844
__________________________________________Typical Operating Characteristics
(Circuit of Figure 2a, VIN = 3.6V, TA = +25°C, unless otherwise noted.)
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2a, VIN = 3.6V, TA = +25°C, unless otherwise noted.)
OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
MAX844
OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE
OSCILLATOR FREQUENCY (kHz)
140
TA = +25°C, +85°C
130
120
TA = -40°C
110
100
90
SHDN = HIGH
80
MAX840-18
31
MAX840-17
150
OSCILLATOR FREQUENCY (kHz)
MAX840/MAX843/MAX844
Low-Noise, Regulated, -2V GaAsFET Bias
29
TA = +25°C, +85°C
27
25
TA = -40°C
23
21
19
SHDN = LOW
17
70
15
2
3
4
5
6
7
8
9
10
2
SUPPLY VOLTAGE (V)
3
4
5
6
7
8
9
10
SUPPLY VOLTAGE (V)
MAX840 OUTPUT NOISE AND RIPPLE
(C1 = C2 = C3 = 1µF, C4 = 10µF)
MAX840 OUTPUT NOISE AND RIPPLE
(C1 = C2 = C3 = 0.22µF, C4 = 4.7µF)
VOUT
1mV/div
VOUT
500µV/div
10µs/div
10µs/div
VIN = 3.6V, VOUT = -2V, IOUT = 4mA, AC COUPLED
VIN = 3.6V, VOUT = -2V, IOUT = 4mA, AC COUPLED
MAX843/MAX844 OUTPUT NOISE AND RIPPLE
(C1 = C2 = C3 = 1µF, C4 = 10µF)
MAX843/MAX844 OUTPUT NOISE AND RIPPLE
(C1 = C2 = C3 = 0.22µF, C4 = 4.7µF)
VOUT
500µV/div
10µs/div
VIN = 3.6V, VOUT = -2V, IOUT = 4mA, AC COUPLED
4
VOUT
1mV/div
10µs/div
VIN = 3.6V, VOUT = -2V, IOUT = 4mA, AC COUPLED
_______________________________________________________________________________________
Low-Noise, Regulated, -2V GaAsFET Bias
MAX840 NOISE SPECTRUM
(C1 = C2 = C3 = 1µF, C4 = 10µF)
40
VIN = 3.6V,
IOUT = 4mA
NOISE (dBµV)
30
20
10
0
-10
0.1
10
1
100
1000
100
1000
100
1000
FREQUENCY (kHz)
MAX840 NOISE SPECTRUM
(C1 = C2 = C3 = 0.22µF, C4 = 4.7µF)
50
VIN = 3.6V,
IOUT = 4mA
NOISE (dBµV)
40
30
20
10
0
0.1
1
10
FREQUENCY (kHz)
MAX843/MAX844 NOISE SPECTRUM
(C1 = C2 = C3 = 1µF, C4 = 10µF)
40
VIN = 3.6V,
IOUT = 4mA
NOISE (dBµV)
30
20
10
0
VOUT
NOTE: dBµV = 20 LOG ______
1µV
-10
0.1
1
10
FREQUENCY (kHz)
_______________________________________________________________________________________
5
MAX840/MAX843/MAX844
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2a, VIN = 3.6V, TA = +25°C, unless otherwise noted.)
____________________________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
VIN = 3.6V,
IOUT = 4mA
40
NOISE (dBµV)
MAX840/MAX843/MAX844
Low-Noise, Regulated, -2V GaAsFET Bias
30
20
10
0
VOUT
NOTE: dBµV = 20 LOG ______
1µV
0.1
10
1
100
1000
FREQUENCY (kHz)
START-UP FROM SHUTDOWN
0V
VOUT
1V/div
VSHDN
2V/div
0V
500µs/div
VIN = 3.6V, VOUT = -2V, IOUT = 4mA
LINE-TRANSIENT RESPONSE
LOAD-TRANSIENT RESPONSE
VOUT
10mV/div
VOUT
20mV/div
3.3V
V
2.7V IN
0.01mA
4mA
5ms/div
VIN = 3.6V, VOUT = -2V
6
IOUT
5ms/div
VOUT = -2V, IOUT = 4mA, AC COUPLED
_______________________________________________________________________________________
Low-Noise, Regulated, -2V GaAsFET Bias
PIN
NAME
FUNCTION
MAX840
MAX843
MAX844
1
1
C1+
Positive Terminal for C1
2
2
C1-
Negative Terminal for C1
3
3
NEGOUT
4
4
SHDN
5
—
FB
—
5
CONT
6
6
OUT
Regulated Negative Output Voltage
7
7
GND
Ground
8
8
IN
Negative Output Voltage (unregulated)
Active-Low, TTL Logic-Level Shutdown Input
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 VOUT, connect a resistor divider between OUT and a
positive control voltage between 0V and 10V (Figure 2c).
Positive Power-Supply Input
Dual Mode is a trademark of Maxim Integrated Products.
C1+
C1-
IN
CHARGE
PUMP
C1+
MAX840
C1-
NEGOUT
N
IN
CHARGE
PUMP
MAX843
MAX844
OUT
NEGOUT
SHDN
N
OUT
FB
CONNECT TO
GND TO SET
VOUT = -2V
SHDN
R2
-0.5V
REF
CONT
R1
GND
Figure 1a. MAX840 Block Diagram
GND
CONTROL
VOLTAGE
Figure 1b. MAX843/MAX844 Block Diagram
_______________________________________________________________________________________
7
MAX840/MAX843/MAX844
______________________________________________________________Pin Description
MAX840/MAX843/MAX844
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 VOUT. In addition, the linear regulator’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 voltage 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 V OUT to
allow proper regulation. The output voltage is calculated from the formula below. Choose R2 to be between
100kΩ and 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)
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 approximately:
ROUT = RO + 4 x ESRC1 + ESRC4 +
1 / (fS x 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 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.
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.
Shutdown Mode
Noise and Ripple Measurement
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.
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
VIN
8
1
C1
1µF
2
3
C2
1µF
4
ON/OFF
8
C3
1µF
IN
C1+
MAX840
C1-
OUT
6
VOUT = -2V
(VGG of GaAsFET)
1
C1
1µF
C4
10µF
NEGOUT
C1+
2
C1-
3
FB
5
ON/OFF
MAX840
4
FB
8
3
C2
1µF
MAX843
MAX844
OUT
6
NEGOUT
R2
100k
CONT
SHDN
GND
7
8
C3
1µF
VOUT = -0.5V to -9.4V @ 4mA
4
ON/OFF
R1
100k
VIN
IN
C1-
5
Figure 2b. MAX840 Adjustable Configuration
VIN
2
)
R2
100k
GND
7
Figure 2a. MAX840 Standard Application Circuit
C1+
(
C4
10µF
SHDN
7
C1
1µF
OUT
R2
VOUT = (-0.5V) 1+
6
R1
NEGOUT
C2
1µF
SHDN
C3
1µF
IN
GND
1
MAX840/MAX843/MAX844
VIN
1
C1
0.22µF
C4
10µF
2
3
C2
0.22µF
C3
0.22µF
IN
C1+
C1-
MAX840
OUT
6
VOUT = -2V
(VGG of GaAsFET)
C4
4.7µF
NEGOUT
5
R1
100k
ON/OFF
4
SHDN
FB
5
GND
VCTRL (0V TO 10V)
Figure 2c. MAX843/MAX844 Standard Application Circuit
7
Figure 2d. MAX840 Application Circuit Using Smaller Capacitors
_______________________________________________________________________________________
9
MAX840/MAX843/MAX844
Low-Noise, Regulated, -2V GaAsFET Bias
___________________Chip Topography
IN
C1+
GND
GND
C1-
0.145"
(3.683mm)
NEGOUT
NEGOUT
OUT
SHDN
FB (CONT)
0.085"
(2.159mm)
( ) ARE FOR MAX843/MAX844
TRANSISTOR COUNT: 148
SUBSTRATE CONNECTED TO IN
10
______________________________________________________________________________________
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