Low-Noise, Regulated, Negative
Charge-Pump Power Supplies for GaAsFET Bias
MAX850–MAX853
______________________________________________________________Pin Description
PIN
MAX850
1
2
3
4
–
–
5
MAX851
1
2
3
–
4
–
5
MAX852
1
2
3
–
–
4
5
MAX853
1
2
3
4
–
–
–
NAME
C1+
C1-
NEGOUT
SHDN
SHDN
OSC
FB
Positive terminal for C1
Negative terminal for C1
FUNCTION
Negative Output Voltage (unregulated), V
NEGOUT
= V
IN
+ 0.2V
Active-low TTL logic level Shutdown Input
Active-high TTL logic level Shutdown Input
External Clock Input
Dual-Mode Feedback Input. When FB is grounded, the output is preset to
-4.1V. To select other output voltages, connect FB to an external resistor
divider. See Figure 2b.
Control Voltage Input. To set V
OUT
, connect a resistor divider between
OUT and a positive control voltage between 0V and 10V. See Figure 2c.
Output Voltage
Ground
Positive Power-Supply Input (4.5V to 10V)
–
6
7
8
–
6
7
8
–
6
7
8
5
6
7
8
CONT
OUT
GND
IN
_______________Detailed Description
The MAX850–MAX853 are low-noise, inverting, regulat-
ed charge-pump power supplies designed for biasing
GaAsFET devices, such as power-amplifier modules in
cellular handsets.
The applied input voltage (V
IN
) is first inverted to a
negative voltage at NEGOUT by a capacitive charge
pump. This voltage is then regulated by an internal lin-
ear regulator, and appears at OUT (Figure 1). The mini-
mum (most negative) output voltage (V
OUT
) achievable
is the inverted positive voltage, plus the 1.0V required
by the post-regulator. The ripple noise induced by the
charge-pump inverter is reduced by the linear regulator
to 2mVp-p at V
OUT
for the MAX850–MAX852. In addi-
tion, the excellent AC rejection of the linear regulator
attenuates noise on the incoming supply. Up to 5mA is
available at OUT.
C1+
C1-
CHARGE
PUMP
IN
C1+
IN
CHARGE
PUMP
NEGOUT
MAX850
MAX851
MAX852
N
C1-
OUT
NEGOUT
MAX853
N
OUT
SHDN (MAX850)
SHDN (MAX851)
OSC (MAX852)
FB
CONNECT TO
GND TO SET
V
OUT
= -4.1V
-1.28V
REF
SHDN
CONT
CONTROL
VOLTAGE
GND
GND
Figure 1a. MAX850–MAX852 Block Diagram
6
Figure 1b. MAX853 Block Diagram
______________________________________________________________________________________
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