General Description
The MAX881R low-noise, inverting power supply is
designed for biasing GaAsFET power amplifiers in
portable wireless applications. This device is a charge-
pump inverter followed by a negative linear regulator.
The input voltage range is 2.5V to 5.5V. The output is
preset at -2.0V or can be set, using two resistors, to any
voltage from -0.5V to (-VIN + 0.6V). It can deliver up to
4mA. The internal linear regulator also filters the output
to 1mVp-p ripple and noise.
Other features include a power-OK (POK) output that sig-
nals when the negative voltage is within 7.5% of its set
point. It protects the GaAsFET by not allowing power to
be applied to the GaAsFET’s drain until it is properly
biased. The signal can be routed either to a microcon-
troller or directly to a switch at the GaAsFET drain. The
MAX881R is available in a 10-pin µMAX package.
Applications
Cell Phones Wireless Modems
PCS Phones Two-Way Pagers
PHS Phones Mobile Radios
Wireless Handsets Wireless Computers
Features
♦Small µMAX Package
♦1mVp-p Output Voltage Ripple and Noise
♦Power-OK Signal to Control GaAsFET Drain
Switch
♦0.05µA Logic-Controlled Shutdown
♦1ms Guaranteed Startup
♦2.5V to 5.5V Input
♦-0.5V to (-VIN + 0.6V) Output at up to 4mA
♦Operates with One 4.7µF and Three 0.22µF
Capacitors (no inductors needed)
MAX881R
Low-Noise Bias Supply in µMAX
with Power-OK for GaAsFET PA
________________________________________________________________ Maxim Integrated Products 1
1
2
3
4
5
10
9
8
7
6
IN
N.C.
GND
OUTPOK
N.C. = NOT INTERNALLY CONNECTED
NEGOUT
C1-
C1+
MAX881R
µMAX
TOP VIEW
FBSHDN
MAX881R
IN OUT
POK
C1+
C1-
NEGOUT FB GND
SHDN
CONTROLS
GaAsFET PA’s
DRAIN SWITCH
OUTPUT
-2V (OR ADJ)
4mA, 1mVp-p
RIPPLE
INPUT
2.5V TO 5.5V
ON OFF
Typical Operating Circuit
19-1372; Rev 2; 1/04
PART
MAX881REUB -40°C to +85°C
TEMP RANGE PIN-PACKAGE
10 µMAX
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.
EVALUATION KIT
AVAILABLE
MAX881R
Low-Noise Bias Supply in µMAX
with Power-OK for GaAsFET PA
2_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 3, VIN = +3.6V, FB = GND, RL= ∞, SHDN = IN, TA= -40°C to +85°C, unless otherwise noted. Typical values are at
TA= +25°C.) (Note 2)
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.
IN to GND .................................................................-0.3V to +6V
SHDN to GND...........................................................-0.3V to +6V
POK to GND ...........................................................-0.3V to +12V
C1+ to GND.................................................-0.3V to (VIN + 0.3V)
C1-, NEGOUT, OUT, FB to GND ....................-6V to (VIN + 0.3V)
Continuous Power Dissipation (TA= +70°C)
10-Pin µMAX (derate 5.6mW/°C above +70°C) ...........444mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +165°C
Lead Temperature (soldering, 10s) .................................+300°C
VIN = 3V, RL= 500Ω, VSHDN = 0 to VIN,
POK goes low
VIN ≥2.5V, IOUT = 0 to 4mA
Connected to IN or GND
VIN = 2.5V
VIN ≥2.7V, IOUT = 0 to 4mA
VIN = 5.5V
VPOK = 11V
IOUT = 4mA, circuit of Figure 3b
VIN ≥2.7V, IOUT = 0 to 4mA
VIN ≥2.5V, sinking 1mA
SHDN = GND
VFB = -0.5V
FB = OUT
CONDITIONS
ms1tSTART
Startup Time
pF10CIN
SHDN Input Capacitance
µA±1ISHDN
SHDN Input Current
V0.35VIL
SHDN Input Low Voltage
V2.2VIH
SHDN Input High Voltage
µA1
POK Off Leakage Current
mV100
POK Output Level
% of
VOUT
90 92.5 95
POK Threshold
kHz80 100 120fOSC
Oscillator Frequency
V-(VIN - 0.6) -0.5VOUT
Adjustable Output Voltage
Range
V-2.1 -2.0 -1.9VOUT
V2.5 5.5VIN
Supply Voltage Range
Preset Output Voltage
mVp-p1Output Ripple
mV/mA26Output Load Regulation
µA0.05 1ISHUT
Shutdown Supply Current
V
-0.515 -0.5 -0.485
VFB
FB Voltage
nA-10 -100FB Input Current
µA500 950IQ
Supply Current (Note 3)
UNITSMIN TYP MAXSYMBOLPARAMETER
Note 1: The output may be shorted to NEGOUT or GND if the package power dissipation is not exceeded. Typical short-circuit
current is 35mA.
-0.525 -0.475
-0.535 -0.465
VIN ≥2.5V,
IOUT = 0 to 4mA
TA= +25°C
TA= 0°C to +85°C
TA= -40°C to +85°C
Note 2: Specifications to -40°C are guaranteed by design, not production tested.
Note 3: MAX881R may draw high supply current during startup, up to the minimum operating supply voltage. To guarantee proper
startup, the input supply must be capable of delivering 90mA more than the maximum load current.
MAX881R
Low-Noise Bias Supply in µMAX
with Power-OK for GaAsFET PA
_______________________________________________________________________________________ 3
-2.02
-1.98
-2.00
-1.94
-1.96
-1.92
1.90
-1.86
-1.88
-1.84
023415678910
OUTPUT VOLTAGE
vs. OUTPUT CURRENT
MAX881R TOC01
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
CIRCUIT OF FIGURE 3a
VIN = 2.5V
VIN ≥ 3.6V
-2.02
-1.98
-2.00
-1.92
-1.94
-1.96
-1.86
-1.88
-1.90
-1.84
06824 1012 14 16
OUTPUT VOLTAGE
vs. OUTPUT CURRENT
MAX881R TOC02
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
CIRCUIT OF FIGURE 3b
VIN = 2.5V
VIN ≥ 3.6V
-2.03
-2.01
-2.02
-1.99
-2.00
-1.98
-1.97
-1.96
-1.95
2.0 3.0 3.52.5 4.0 4.5 5.0 5.5 6.0
OUTPUT VOLTAGE
vs. INPUT VOLTAGE
MAX881R TOC03
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
ILOAD = 4mA
Typical Operating Characteristics
(Circuit of Figure 3, VIN = 3.6V, TA= +25°C, unless otherwise noted.)
0
10
5
25
20
15
40
35
30
45
2.0 3.5 4.02.5 3.0 4.5 5.0 5.5 6.0
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
MAX881r TOC04
INPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
VOUT < 2mVp-p RIPPLE
CIRCUIT OF FIGURE 3b
VOUT < 2mVp-p RIPPLE
CIRCUIT OF FIGURE 3a
VOUT ≤ -1.8V
CIRCUIT OF FIGURE 3a
VOUT ≤ -1.8V
CIRCUIT OF FIGURE 3b
0
4
8
12
16
20
24
2.0 3.02.5 3.5 4.0 4.5 5.0 5.5 6.0
MAXIMUM NEGOUT CURRENT
vs. INPUT VOLTAGE
MAX881R TOC05
INPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
VNEGOUT = 0.9 x VNEGOUT(NO LOAD)
CIRCUIT OF FIGURE 3b
CIRCUIT OF FIGURE 3a
300
400
500
600
700
800
900
2.0 3.02.5 3.5 4.0 4.5 5.0 5.5 6.0
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX881R TOC06
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
300
400
500
600
700
800
900
-60 -20-40 0 20 40 60 80 100
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
MAX881R TOC07
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
VIN = 5.5V
VIN = 3.6V
VIN = 2.5V
100
300
200
500
400
700
600
800
2.0 3.0 3.52.5 4.0 4.5 5.0 5.5 6.0
STARTUP TIME
vs. INPUT VOLTAGE
MAX881R TOC08
INPUT VOLTAGE (V)
START-UP TIME (µs)
CIRCUIT OF FIGURE 3a
NO LOAD
SHDN TO POK DELAY
97
98
99
100
101
102
103
2.0 3.02.5 3.5 4.0 4.5 5.0 5.5 6.0
OSCILLATOR FREQUENCY
vs. INPUT VOLTAGE
MAX881R TOC09
INPUT VOLTAGE (V)
FREQUENCY (kHz)
TA = -40°C
TA = +25°C
TA = +85°C
MAX881R
Low-Noise Bias Supply in µMAX
with Power-OK for GaAsFET PA
4_______________________________________________________________________________________
Typical Operating Characteristics (continued)
(Circuit of Figure 3, VIN = 3.6V, TA= +25°C, unless otherwise noted.)
100µs/div
STARTUP FROM SHUTDOWN
(NO LOAD)
+5V
VOUT
POK
SHDN
MAX881R-TOC10
-2V
0
0
VIN
0
VIN = 3.6V
CIRCUIT OF FIGURE 3b
5µs/div
OUTPUT NOISE AND RIPPLE
(CIRCUIT OF FIGURE 3a)
VOUT
1mV/div
AC-COUPLED
MAX881R-TOC11
VIN = 3.6V
VOUT = -2V
IOUT = 2.5mA
60
-40
110100 1000
OUTPUT NOISE SPECTRUM
(CIRCUIT OF FIGURE 3a)
-20
MAX881R TOC13
FREQUENCY (kHz)
NOISE (dBµV)
0
20
40
50
-30
-10
10
30
VIN = 3.6V
VOUT = -2V
IOUT = 2.5mA
60
-40
110100 1000
OUTPUT NOISE SPECTRUM
(CIRCUIT OF FIGURE 3b)
-20
MAX881R TOC14
FREQUENCY (kHz)
NOISE (dBµV)
0
20
40
50
-30
-10
10
30
VIN = 3.6V
VOUT = -2V
IOUT = 4mA
2ms/div
LINE-TRANSIENT RESPONSE
VIN
VOUT
MAX881R-TOC15
10mV/
div
3.3V
2.7V
ILOAD = 4mA
VOUT = -2V
CIRCUIT OF FIGURE 3b
100µs/div
LOAD-TRANSIENT RESPONSE
IOUT
VOUT
MAX881R-TOC16
10mV/
div
4mA
400µA
VIN = 3.6V
VOUT = -2V
CIRCUIT OF FIGURE 3b
MAX881R
Low-Noise Bias Supply in µMAX
with Power-OK for GaAsFET PA
_______________________________________________________________________________________ 5
CHARGE PUMP
NEGOUT
SHDN
0.5V 0.4625V
GND
C1+
C1
C2 C4
C3
IN
OUT
FB
POK
C1-
MAX881R
Pin Description
Figure 1. Functional Diagram
Dual Mode is a trademark of Maxim Integrated Products.
PIN FUNCTION
1Positive Terminal for C1
2Negative Terminal for C1
3Negative Output Voltage (unregulated)
4Active-Low, Open-Drain Power-OK Output. Goes low when OUT reaches 92.5% of its set
value.
5Active-Low, Logic-Level Shutdown Input. Connect to IN for normal operation. Do not leave this
pin unconnected.
6
Dual-Mode™ Feedback Input. When FB is connected to GND, the output is preset to -2V. To
select other voltages, connect FB to an external resistor-divider (Figure 4). Do not leave this pin
unconnected.
7Regulated Negative Output Voltage
8Ground
9No Connection. Not internally connected.
10 Positive Power-Supply Input
C1+
C1-
NEGOUT
POK
SHDN
FB
OUT
GND
N.C.
IN
NAME
MAX881R
Low-Noise Bias Supply in µMAX
with Power-OK for GaAsFET PA
6_______________________________________________________________________________________
Detailed Description
The MAX881R, a low-noise, inverting, regulated charge-
pump power supply, is designed for biasing GaAsFET
devices such as power-amplifier modules in cellular
handsets.
The applied input voltage (VIN) is inverted to a negative
voltage at NEGOUT by a capacitive charge pump. This
voltage is regulated by an internal linear regulator at
OUT (Figure 1). With FB connected to GND, VOUT is
regulated at -2V. Alternatively, use a voltage-divider at
FB to adjust the output voltage between -0.5V and -(VIN
- 0.6V) (see the section Setting the Output Voltage).
The internal linear regulator reduces the ripple noise
induced by the charge-pump inverter to 1mVp-p at
OUT (circuit of Figure 3b). In addition, the excellent AC
rejection of the linear regulator attenuates noise from
the incoming supply.
Power-OK Signal
The MAX881R has an active-low, open-drain, power-OK
(POK) output. This output goes low when OUT reaches
92.5% of the regulated output voltage. POK can be
used to drive the gate of a P-MOSFET that switches
power to the GaAsFET power amplifier (Figure 2), there-
by ensuring that the power amplifier is not powered
before the required negative bias voltage is present.
Use a 50kΩor larger pull-up resistor to signal a logic
high when POK goes high impedance.
Shutdown Mode
The MAX881R features a shutdown mode that reduces
supply current to less than 1µA over temperature. SHDN
is an active-low, logic-level input. Start-up time coming
out of shutdown mode is typically 0.5ms. OUT and
NEGOUT are switched to GND in shutdown mode.
Applications Information
Setting the Output Voltage
Select either a fixed or adjustable output for the
MAX881R. Connect FB to GND for a fixed -2V output
(Figure 3). Select an alternative output voltage by con-
necting FB to the midpoint of a resistor-divider from
OUT to GND (Figure 4). When operating under full load
(4mA), the voltage at IN should be at least 0.6V higher
than the absolute voltage required at OUT. Note that
the minimum input voltage required for operation is
2.5V, regardless of the desired output voltage.
Choose R1 to be between 100kΩand 400kΩand cal-
culate R2. For greater accuracy, use resistors with 1%
or better tolerance.
R2 = R1 (2 x |VOUT|- 1)
POK
100k
C4
VCC FOR
POWER AMPLIFIER
TO PA
GATE BIAS
TO
POWER
AMPLIFIER
OUT
MAX881R
P
Figure 2. Using the
POK
Function
NEGOUT
SHDN
C1-
C1+
POK
VOUT = -2V
C3
0.22µF
C2
0.22µF
C1
0.22µFC4
4.7µF
ON
VIN
OFF
OUT
IN
GND FB
MAX881R
Figure 3a. Standard Application Circuit for Minimum Capacitor
Values
NEGOUT
SHDN
C1-
C1+
POK
VOUT = -2V
C3
1µF
C2
1µF
C1
1µFC4
10µF
VIN
OUT
IN
GND FB
MAX881R
ON
OFF
Figure 3b. Standard Application Circuit for Minimum Output
Noise
MAX881R
Low-Noise Bias Supply in µMAX
with Power-OK for GaAsFET PA
_______________________________________________________________________________________ 7
Capacitors
Use capacitors with a low effective series resistance
(ESR) to maintain a low dropout voltage (VIN - |VOUT|).
The overall dropout voltage is a function of the output
resistance of the charge pump and the voltage drop
across the linear regulator (N-channel pass transistor).
At the 100kHz charge-pump switching frequency, out-
put resistance is a function of the value of C1 and the
ESR of C1 and C2. Therefore, increasing C1 and mini-
mizing the ESR of the charge-pump capacitors mini-
mizes dropout voltage.
The output resistance of the entire circuit (in dropout) is
approximately:
ROUT = RO+ 4 x ESRC1 + ESRC2 + 1 / (fSx C1)
+ R(linear regulator)
Where R(linear regulator) (the output impedance of the
linear regulator) is approximately 2Ωand RO(the resis-
tance of the internal switches) is typically 10Ω. When
regulating, the output resistance of the circuit is simply
the linear-regulator load regulation (2mV/mA).
C1, C2, and C3 should be 0.22µF capacitors with less
than 0.4ΩESR. C4 should be a 4.7µF capacitor with
less than 0.1ΩESR. Larger capacitor values can be
used (C1 = C2 = C3 = 1µF, C4 = 10µF) to reduce out-
put noise and ripple (1mVp-p), at the expense of cost
and board space. All capacitors should be either
ceramic or surface-mount chip tantalum (Figures 3a
and 3b).
Layout and Grounding
Good layout is important for good noise performance.
To optimize the layout:
1) Mount all components as close together as possible.
2) Keep traces short to minimize parasitic inductance
and capacitance, especially 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 circuit and the oscilloscope
(which result from the charge pump’s switching action)
cause ground currents in the probes’ wires, inducing
sharp voltage spikes. For best results, measure directly
across the output capacitor (C4). Do not use the
ground lead of the probe; instead, remove the probe’s
tip cover and touch the ground ring on the probe
directly to C4’s ground terminal. This direct connection
gives the most accurate noise and ripple measurement.
NEGOUT
SHDN
C1-
C1+
POK
FB
C3
0.22µF
C2
0.22µF
C1
0.22µF
C4
4.7µF
VIN
OUT
R2
R1
IN
GND
MAX881R
ON
OFF
Figure 4. Adjustable Output Configuration
TRANSISTOR COUNT: 413
Chip Information
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
MAX881R
Low-Noise Bias Supply in µMAX
with Power-OK for GaAsFET PA
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.
8_____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
©2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
10LUMAX.EPS
PACKAGE OUTLINE, 10L uMAX/uSOP
1
1
21-0061 I
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
TOP VIEW
FRONT VIEW
1
0.498 REF
0.0196 REF
S
6°
SIDE VIEW
α
BOTTOM VIEW
0° 0° 6°
0.037 REF
0.0078
MAX
0.006
0.043
0.118
0.120
0.199
0.0275
0.118
0.0106
0.120
0.0197 BSC
INCHES
1
10
L1
0.0035
0.007
e
c
b
0.187
0.0157
0.114
H
L
E2
DIM
0.116
0.114
0.116
0.002
D2
E1
A1
D1
MIN
-A
0.940 REF
0.500 BSC
0.090
0.177
4.75
2.89
0.40
0.200
0.270
5.05
0.70
3.00
MILLIMETERS
0.05
2.89
2.95
2.95
-
MIN
3.00
3.05
0.15
3.05
MAX
1.10
10
0.6±0.1
0.6±0.1
00.50±0.1
H
4X S
e
D2
D1
b
A2 A
E2
E1 L
L1
c
α
GAGE PLANE
A2 0.030 0.037 0.75 0.95
A1