Low-Noise, Regulated, Negative
Charge-Pump Power Supplies for GaAsFET Bias
MAX850–MAX853
sensitivity and interference. The clock must be a square wave
between 40% and 60% duty cycle. The maximum clock fre-
quency is 250kHz, and the minimum frequency is 50kHz.
___________________Chip Topography
C1+
IN
Layout and Grounding
Good layout is important, primarily for good noise perfor-
mance.
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.
C1-
GND
0.127"
(3.226mm)
NEGOUT
Noise and Ripple Measurement
Accurately measuring the output noise and ripple is a chal-
lenge. Brief differences in ground potential between the
MAX850–MAX853 circuit and the oscilloscope (which result
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 capaci-
tor (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 rip-
ple measurement.
OUT
FB (MAX850–852)
CONT (MAX853)
SHDN (MAX850/853)
SHDN (MAX851)
OSC (MAX852)
0.085"
(2.159mm)
TRANSISTOR COUNT: 164
SUBSTRATE CONNECTED TO IN
________________________________________________________Package Information
DIM
A
A1
B
C
D
E
e
H
h
L
α
INCHES
MAX
MIN
0.069
0.053
0.010
0.004
0.019
0.014
0.010
0.007
0.197
0.189
0.157
0.150
0.050 BSC
0.244
0.228
0.020
0.010
0.050
0.016
8˚
0˚
MILLIMETERS
MIN
MAX
1.35
1.75
0.10
0.25
0.35
0.49
0.19
0.25
4.80
5.00
3.80
4.00
1.27 BSC
5.80
6.20
0.25
0.50
0.40
1.27
0˚
8˚
21-325A
E
H
D
A
e
B
0.127mm
0.004in.
h x 45˚
α
A1
C
L
8-PIN PLASTIC
SMALL-OUTLINE
PACKAGE
8
______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
