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19-0388; Rev 1; 3/96
L MANUA ION KIT ALUAT DATA SHEET EV WS FOLLO
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 0.22F. 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 750A, and reduces to less than 1A 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.
____________________________Features
o Fixed -2V or Adjustable -0.5V to -9.4V Output at 4mA (MAX840) o 2.5V to 10V Input Voltage Range o Operate with Small Capacitors (as low as 0.22F) o 1mVp-p Output Voltage Ripple o Charge-Pump Switching Frequency: 100kHz in Normal Operation 20kHz in Shutdown Mode (MAX844) o 1A Max Logic-Level Shutdown Over Temp. (MAX840/MAX843) o Small 8-Pin SO Package
MAX840/MAX843/MAX844
______________Ordering Information
PART MAX840C/D MAX840ISA MAX840ESA MAX843C/D MAX843ISA MAX843ESA MAX844C/D MAX844ISA MAX844ESA TEMP. RANGE 0C to +70C -25C to +85C -40C to +85C 0C to +70C -25C to +85C -40C to +85C 0C to +70C -25C to +85C -40C to +85C PIN-PACKAGE Dice* 8 SO 8 SO Dice* 8 SO 8 SO Dice* 8 SO 8 SO
________________________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)
* Dice are specified at TA = +25C only.
0.22F IN C1+ 0.22F C1VOUT = -2.0V (VGG of GaAsFET) OUT 4.7F NEGOUT 0.22F
__________________Pin Configuration
TOP VIEW
MAX840
C1+ 1 C1- 2 NEGOUT 3 SHDN 4
8
IN GND OUT FB (CONT)
MAX840 MAX843 MAX844
7 6 5
ON/OFF
SHDN GND
FB
SO
( ) 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
Low-Noise, Regulated, -2V GaAsFET Bias MAX840/MAX843/MAX844
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 ...................................................-25C to +85C VIN to VNEGOUT.........................................................-0.3V to 21V MAX84_E_ _A ..................................................-40C to +85C VOUT to GND (Note 1).......................................VNEGOUT to 0.3V Storage Temperature Range .............................-65C to +150C V SHDN to GND ............................................-0.3V to (VIN + 0.3V) Lead Temperature (soldering, 10sec) .............................+300C Continuous Power Dissipation (TA = +70C) SO (derate 5.88mW/C above +70C) .........................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 = +25C.) PARAMETER Supply Voltage Range SYMBOL VIN VIN 2.5V, IOUT = 0mA to 3mA VIN 2.7V, IOUT = 0mA to 4mA VIN 2.5V, IOUT = 0mA to 3mA VIN 2.7V, IOUT = 0mA to 4mA CONDITIONS MIN 2.5 -2.1 -2.1 -2.05 -2.05 -2.0 -2.0 -2.0 -2.0 -0.5 to (VIN - 0.6) MAX840, no load MAX840, VFB = -0.5V MAX843/MAX844, VCONT = 0V No load, VIN 3.6V MAX840/MAX843, VIN = 10V, SHDN = 0V Shutdown Supply Current ISHUT MAX844, VIN = 10V, SHDN = 0V MAX844, VIN 3.6V, SHDN = 0V VOUT Load Regulation VOUT Ripple Oscillator Frequency Input High Voltage Input Low Voltage Input Current Input Capacitance 2 FOSC VIH VIL IIN CIN VIN = 3.6V, RL = or 500 C4 = 10F VIN = 3.6V, TA = +25C SHDN SHDN SHDN SHDN -1 10 MAX840/MAX843/ MAX844 MAX844, SHDN = 0V 80 14 2.2 0.35 1 MAX840, VFB = 0V MAX843/MAX844, VCTRL = 2V 940 175 3 2 1 100 20 120 26 V V A pF 300 8 8 mV/mA mVp-p kHz -0.516 -0.5 1 1 750 -0.484 100 100 1300 1 A TYP MAX 10 -1.9 -1.9 V -1.95 -1.95 V V nA nA A UNITS V
MAX840, VFB = 0V Output Voltage VOUT MAX843/MAX844, VCTRL = 2V
Output Voltage Adjust Range FB Voltage FB Leakage Current CONT Leakage Current Supply Current
VOUT VFB IFB ICONT IQ
_______________________________________________________________________________________
Low-Noise, Regulated, -2V GaAsFET Bias
__________________________________________Typical Operating Characteristics
(Circuit of Figure 2a, VIN = 3.6V, TA = +25C, unless otherwise noted.)
MAX840/MAX843/MAX844
OUTPUT VOLTAGE vs. OUTPUT CURRENT
MAX840-01
OUTPUT VOLTAGE vs. INPUT VOLTAGE OVER TEMPERATURE
MAX840-02
-2.070
-2.065
-2.060 OUTPUT VOLTAGE (V) -2.060 OUTPUT VOLTAGE (V)
-2.055
TA = +85C TA = +25C TA = -40C
-2.050
-2.050
-2.045
-2.040 0 1 2 3 4 5 6 7 8 9 10 OUTPUT CURRENT (mA)
-2.040 2 3 4 5 6 7 8 9 10 INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE
MAX840-03
NEGOUT CURRENT vs. INPUT VOLTAGE
VNEGOUT = 0.9 x VNEGOUT(NO LOAD) 25 NEGOUT CURRENT (mA) 20 15 10 5 0 SHUTDOWN (MAX844)
MAX840-04
120 MAXIMUM OUTPUT CURRENT (mA) 100 80 60 40 20 0 2 3 4 5 6 7 8 9 VOUT < -1.95V (CIRCUIT OF FIG 2a) VOUT < -1.95V (CIRCUIT OF FIG 2d)
30
High-current operation not recommended for extended periods of time.
VOUT < 2mVp-p RIPPLE (CIRCUIT OF FIG 2a) VOUT < 2mVp-p RIPPLE (CIRCUIT OF FIG 2d) 10
2
3
4
5
6
7
8
9
10
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
N0-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE
MAX840-05
SUPPLY CURRENT vs. TEMPERATURE
MAX840-06
START-UP TIME vs. INPUT VOLTAGE
MAX840-07
5 NO-LOAD SUPPLY CURRENT (mA)
7 6 SUPPLY CURRENT (mA) 5 VIN = 10V 4 3 2 1 VIN = 3.6V
2.8 2.4 START-UP TIME (ms) 2.0 1.6 1.2 0.8 0.4
4
3
2
1
0 2 3 4 5 6 7 8 9 10 INPUT VOLTAGE (V)
0 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
2
3
4
5
6
7
8
9
10
INPUT VOLTAGE (V)
_______________________________________________________________________________________
3
Low-Noise, Regulated, -2V GaAsFET Bias MAX840/MAX843/MAX844
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2a, VIN = 3.6V, TA = +25C, unless otherwise noted.)
OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE
MAX840-17
MAX844 OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE
29 27 25 TA = -40C 23 21 19 17 15 10 SHDN = LOW TA = +25C, +85C
MAX840-18
150 OSCILLATOR FREQUENCY (kHz) 140 130 120 110 100 90 80 70 2 3 4 5 6 7 8 9 SUPPLY VOLTAGE (V) SHDN = HIGH TA = +25C, +85C TA = -40C
31 OSCILLATOR FREQUENCY (kHz)
2
3
4
5
6
7
8
9
10
SUPPLY VOLTAGE (V)
MAX840 OUTPUT NOISE AND RIPPLE (C1 = C2 = C3 = 1F, C4 = 10F)
MAX840 OUTPUT NOISE AND RIPPLE (C1 = C2 = C3 = 0.22F, C4 = 4.7F)
VOUT 500V/div
VOUT 1mV/div
10s/div VIN = 3.6V, VOUT = -2V, IOUT = 4mA, AC COUPLED
10s/div VIN = 3.6V, VOUT = -2V, IOUT = 4mA, AC COUPLED
MAX843/MAX844 OUTPUT NOISE AND RIPPLE (C1 = C2 = C3 = 1F, C4 = 10F)
MAX843/MAX844 OUTPUT NOISE AND RIPPLE (C1 = C2 = C3 = 0.22F, C4 = 4.7F)
VOUT 500V/div
VOUT 1mV/div
10s/div VIN = 3.6V, VOUT = -2V, IOUT = 4mA, AC COUPLED
10s/div VIN = 3.6V, VOUT = -2V, IOUT = 4mA, AC COUPLED
4
_______________________________________________________________________________________
Low-Noise, Regulated, -2V GaAsFET Bias
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2a, VIN = 3.6V, TA = +25C, unless otherwise noted.)
MAX840/MAX843/MAX844
MAX840 NOISE SPECTRUM (C1 = C2 = C3 = 1F, C4 = 10F)
40 VIN = 3.6V, IOUT = 4mA
30 NOISE (dBV)
20
10
0
-10 0.1 1 10 FREQUENCY (kHz) 100 1000
MAX840 NOISE SPECTRUM (C1 = C2 = C3 = 0.22F, C4 = 4.7F)
50 VIN = 3.6V, IOUT = 4mA
40 NOISE (dBV)
30
20
10
0 0.1 1 10 FREQUENCY (kHz) 100 1000
MAX843/MAX844 NOISE SPECTRUM (C1 = C2 = C3 = 1F, C4 = 10F)
40 VIN = 3.6V, IOUT = 4mA
30 NOISE (dBV)
20
10
0
VOUT NOTE: dBV = 20 LOG ______ 1V
-10 0.1 1 10 FREQUENCY (kHz) 100 1000
_______________________________________________________________________________________
5
Low-Noise, Regulated, -2V GaAsFET Bias MAX840/MAX843/MAX844
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2a, VIN = 3.6V, TA = +25C, unless otherwise noted.)
MAX843/MAX844 NOISE SPECTRUM (C1 = C2 = C3 = 0.22F, C4 = 4.7F)
50 VIN = 3.6V, IOUT = 4mA
40 NOISE (dBV)
30
20
10
0
VOUT NOTE: dBV = 20 LOG ______ 1V
0.1
1
10 FREQUENCY (kHz)
100
1000
START-UP FROM SHUTDOWN
0V
VOUT 1V/div
VSHDN 2V/div 0V
500s/div VIN = 3.6V, VOUT = -2V, IOUT = 4mA
LOAD-TRANSIENT RESPONSE
LINE-TRANSIENT RESPONSE
VOUT 20mV/div
VOUT 10mV/div
0.01mA 4mA IOUT
3.3V V 2.7V IN
5ms/div VIN = 3.6V, VOUT = -2V
5ms/div VOUT = -2V, IOUT = 4mA, AC COUPLED
6
_______________________________________________________________________________________
Low-Noise, Regulated, -2V GaAsFET Bias
______________________________________________________________Pin Description
PIN MAX840 1 2 3 4 5 MAX843 MAX844 1 2 3 4 -- NAME FUNCTION
MAX840/MAX843/MAX844
C1+ C1NEGOUT SHDN FB
Positive Terminal for C1 Negative Terminal for C1 Negative Output Voltage (unregulated) Active-Low, TTL Logic-Level Shutdown Input Dual ModeTM 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). Regulated Negative Output Voltage Ground Positive Power-Supply Input
-- 6 7 8
5 6 7 8
CONT OUT GND IN
Dual Mode is a trademark of Maxim Integrated Products.
C1+ C1CHARGE PUMP
IN C1+ IN CHARGE PUMP
MAX840
C1N OUT NEGOUT
NEGOUT
N
MAX843 MAX844
OUT
SHDN
FB CONNECT TO GND TO SET VOUT = -2V -0.5V REF SHDN
R2
CONT
R1
GND GND CONTROL VOLTAGE
Figure 1a. MAX840 Block Diagram
Figure 1b. MAX843/MAX844 Block Diagram
_______________________________________________________________________________________
7
Low-Noise, Regulated, -2V GaAsFET Bias MAX840/MAX843/MAX844
_______________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.
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 71 at VIN = 2.5V, 48 at VIN = 5V, and 40 at VIN = 10V. C1, C2, and C3 should be 1F capacitors with less than 0.8 ESR. C4 should be a 10F capacitor with less than 0.2 ESR. Smaller capacitor values can be used (C1 = C2 = C3 = 0.22F, C4 = 4.7F) 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.
__________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 100k and 400k. 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)
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
The MAX840/MAX843/MAX844 feature a shutdown mode that reduces the supply current to 1A max over temperature (300A 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.
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
VIN
VIN
8 1
C1 1F IN C1+
C3 1F VOUT = -2V (VGG of GaAsFET) C4 10F C2 1F C1 1F
8 1 2 3 IN C1+
C3 1F R2 VOUT = (-0.5V) 1+ 6 R1
2 3
C1-
MAX840
OUT
6
C1-
MAX840
OUT
(
)
C2 1F
NEGOUT
NEGOUT
C4 10F R2 100k
ON/OFF
4
SHDN GND
FB
5
ON/OFF
4
SHDN GND 7
FB
5 R1 100k
7
Figure 2a. MAX840 Standard Application Circuit
Figure 2b. MAX840 Adjustable Configuration
VIN 8 1 C1 1F 2 3 C2 1F 4 ON/OFF SHDN GND 7 C1+ IN C3 1F VOUT = -0.5V to -9.4V @ 4mA C1C1 0.22F
VIN 8 1 2 3 C2 0.22F 4 IN C1+ C3 0.22F VOUT = -2V (VGG of GaAsFET) C4 4.7F
MAX843 MAX844
OUT
6 R2 100k
NEGOUT
C4 10F
C1-
MAX840
OUT
6
NEGOUT
CONT
5 R1 100k ON/OFF SHDN GND FB 5
VCTRL (0V TO 10V)
7
Figure 2c. MAX843/MAX844 Standard Application Circuit
Figure 2d. MAX840 Application Circuit Using Smaller Capacitors
_______________________________________________________________________________________
9
Low-Noise, Regulated, -2V GaAsFET Bias MAX840/MAX843/MAX844
___________________Chip Topography
IN C1+
GND GND
C1NEGOUT NEGOUT
0.145" (3.683mm)
OUT
SHDN 0.085" (2.159mm)
FB (CONT)
( ) ARE FOR MAX843/MAX844 TRANSISTOR COUNT: 148 SUBSTRATE CONNECTED TO IN
10
______________________________________________________________________________________

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