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 RangeOperate with Small Capacitors (as low as 0.22µF)1mVp-p Output Voltage RippleCharge-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*
0°C to +70°C Dice*
Dice* 8 SO 8 SO
MAX840/MAX843/MAX844
__________________Pin Configuration
TOP VIEW
1
C1+
2
C1-
NEGOUT
3
SHDN
4
( ) ARE FOR MAX843/MAX844
MAX840 MAX843 MAX844
SO
Maxim Integrated Products
8 7 6 5
IN GND OUT
FB (CONT)
1
0.22µF
0.22µF
ON/OFF
0.22µF
C1+
C1-
NEGOUT
SHDN 
________________________________________________________________
IN
MAX840
GND
OUT
= -2.0V
V
OUT
of GaAsFET)
(V
GG
4.7µF
FB
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
V
IN
V
OUT
V
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
IN
.........................................................-0.3V to 21V
to 0.3V
= +70°C)
A
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
V
V
FB Voltage FB Leakage Current CONT Leakage Current
CONT
Supply Current µA750 1300
Shutdown Supply Current
V
Load Regulation
OUT
Ripple
OUT
I
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
IN
MAX840, VFB= 0V
OUT
MAX843/MAX844, V
= 2V
CTRL
OUT
MAX840, no load
FB
FB
MAX840, VFB= -0.5V MAX843/MAX844, V No load, VIN≤ 3.6VI
Q
MAX840/MAX843, VIN= 10V, SHDN = 0V MAX844, VIN= 10V, SHDN = 0V MAX844, VIN≤ 3.6V, SHDN = 0V
VIN= 3.6V, RL= or 500
C4 = 10µF
OSC
VIN= 3.6V, TA= +25°C
SHDN 2.2 V
IH
SHDN 0.35 V
IL
SHDN -1 1 µA
IN
SHDN 10 pF
IN
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,
I
= 0mA to 3mA
OUT
VIN≥ 2.7V,
I
= 0mA to 4mA
OUT
VIN≥ 2.5V,
I
= 0mA to 3mA
OUT
VIN≥ 2.7V,
I
= 0mA to 4mA
OUT
-2.1 -2.0 -1.9
-2.1 -2.0 -1.9
-2.05 -2.0 -1.95
-2.05 -2.0 -1.95
-0.5 to
- 0.6)
(V
IN
= 0V
CONT
1 940 175 300
MAX840, VFB= 0V MAX843/MAX844,
V
= 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
V
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)
6
MAXIMUM OUTPUT CURRENT 
vs. INPUT VOLTAGE
120
100
80
60
V
(CIRCUIT OF FIG 2d)
(CIRCUIT OF FIG 2a)
< -1.95V
OUT
V
< -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
A
-2.050
OUTPUT VOLTAGE (V)
-2.045
-2.040
TA = +25°C
TA = -40°C
INPUT VOLTAGE (V)
NEGOUT CURRENT vs. INPUT VOLTAGE
30
V
= 0.9 x V
NEGOUT
25
20
15
NEGOUT(NO LOAD)
MAX840-02
10624 83579
MAX840-04
MAX840/MAX843/MAX844
40
20
MAXIMUM OUTPUT CURRENT (mA)
0
24 83579
INPUT VOLTAGE (V)
N0-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
5
4
3
2
1
NO-LOAD SUPPLY CURRENT (mA)
0
24 83579
6
INPUT VOLTAGE (V)
_______________________________________________________________________________________
V
< 2mVp-p RIPPLE
OUT
(CIRCUIT OF FIG 2a)
V
< 2mVp-p RIPPLE
OUT
(CIRCUIT OF FIG 2d)
6
10
10
NEGOUT CURRENT (mA)
5
0
24 83579
INPUT VOLTAGE (V)
SUPPLY CURRENT vs. TEMPERATURE
7
MAX840-05
SUPPLY CURRENT (mA)
10
6
5
4
3
2
1
0
VIN = 10V
VIN = 3.6V
-40 0 80-20 20 60 100 TEMPERATURE (°C)
40
MAX840-06
START-UP TIME (ms)
SHUTDOWN
(MAX844)
6
10
START-UP TIME vs. INPUT VOLTAGE
2.8
2.4
2.0
1.6
1.2
0.8
0.4 24 8357910
6
INPUT VOLTAGE (V)
MAX840-07
3
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
90
OSCILLATOR FREQUENCY (kHz)
80 70
T
24 83579
SUPPLY VOLTAGE (V)
= +25°C, +85°C
A
6
MAX840-17
TA = -40°C
SHDN = HIGH
10
MAX840 OUTPUT NOISE AND RIPPLE
(C1 = C2 = C3 = 1µF, C4 = 10µF)
MAX840/MAX843/MAX844
V
OUT
500µV/div
OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE
MAX844
31 29 27 25 23 21 19
OSCILLATOR FREQUENCY (kHz)
17 15
24 83579
T
= +25°C, +85°C
A
TA = -40°C
SHDN = LOW
6
SUPPLY VOLTAGE (V)
MAX840 OUTPUT NOISE AND RIPPLE (C1 = C2 = C3 = 0.22µF, C4 = 4.7µF)
MAX840-18
10
V
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
V
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
= -2V, I
10µs/div
= 4mA, AC COUPLED
OUT
10µs/div
= 4mA, AC COUPLED
OUT
4 _______________________________________________________________________________________
V
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
40
VIN = 3.6V, I
OUT
30
20
10
NOISE (dBµV)
0
-10
0.1 1
50
VIN = 3.6V, I
OUT
40
= 4mA
= 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
V
OUT
______
1µV
30
20
NOISE (dBµV)
10
0
0.1 1
40
VIN = 3.6V, I
OUT
30
20
10
NOISE (dBµV)
0
-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)
_______________________________________________________________________________________
5
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)
50
VIN = 3.6V,
= 4mA
I
OUT
40
30
20
NOISE (dBµV)
10
0
NOTE: dBµV = 20 LOG
V
OUT
______
1µV
0.1 1 FREQUENCY (kHz)
START-UP FROM SHUTDOWN
MAX840/MAX843/MAX844
0V
0V
500µs/div
VIN = 3.6V, V
LOAD-TRANSIENT RESPONSE
= -2V, I
OUT
V
OUT
20mV/div
OUT
10 100 1000
V
OUT
1V/div
V
SHDN
2V/div
= 4mA
LINE-TRANSIENT RESPONSE
V
OUT
10mV/div
0.01mA I
OUT
4mA
5ms/div
= 4mA, AC COUPLED
VIN = 3.6V, V
OUT
= -2V
5ms/div
V
OUT
= -2V, I
OUT
6 _______________________________________________________________________________________
3.3V
2.7V
V
IN
Low-Noise, Regulated, -2V GaAsFET Bias
______________________________________________________________Pin Description
PIN
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
5
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
N
C1-
NEGOUT
SHDN
Figure 1a. MAX840 Block Diagram
_______________________________________________________________________________________ 7
MAX840
GND
IN
OUT
FB
CONNECT TO  GND TO SET V
= -2V
OUT
C1+
CHARGE
C1-
PUMP
MAX843 MAX844
GND
SHDN
NEGOUT
N
Figure 1b. MAX843/MAX844 Block Diagram
IN
OUT
CONT
CONTROL VOLTAGE
R2
R1
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 100kand 400k.
V
= (-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
= -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
IN
to
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:
R
= 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 71at VIN= 2.5V, 48at VIN= 5V, and 40at VIN= 10V.
C1, C2, and C3 should be 1µF capacitors with less than
0.8ESR. C4 should be a 10µF capacitor with less than 0.2ESR. 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)
(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
V
IN
8
1
C1+
2
C1-
3
NEGOUT
45
SHDN
IN
MAX840
GND
OUT
FB
C3 1µF
= -2V
V
OUT
of GaAsFET)
(V
6
GG
C4 10µF
7
C1
1µF
C2
1µF
ON/OFF
1
2
3
4
C1+
C1-
NEGOUT
SHDN
V
IN
IN
MAX840
GND
8
V
= (-0.5V) 1+
OUT
6
OUT
R2 100k
5
FB
R1
7
100k
Figure 2a. MAX840 Standard Application Circuit Figure 2b. MAX840 Adjustable Configuration
C1
1µF
C2
1µF
ON/OFF
V
IN
8
1
C1+
2
C1-
3
NEGOUT
45
SHDN
IN
V
OUT
MAX843 MAX844
OUT
6
CONT
GND
7
V
(0V TO 10V)
CTRL
= -0.5V to -9.4V @ 4mA
R2 100k
R1 100k
C3 1µF
C4 10µF
0.22µF
0.22µF
ON/OFF
1
C1
2
3
C2
45
C1+
C1-
NEGOUT
SHDN
V
IN
8
IN
MAX840
GND
7
6
OUT
FB
C3
0.22µF
V
OUT
of GaAsFET)
(V
GG
C4
4.7µF
C3 1µF
R2
( )
R1
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
IN
C1+
GND GND
NEGOUT
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 ______________________________________________________________________________________
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