MAX851 MAXIM [Maxim Integrated Products], MAX851 Datasheet - Page 8

• Manufacturer Part Number: MAX851
• Description: Low-Noise, Regulated, Negative Charge-Pump Power Supplies for GaAsFET Bias
• Manufacturer: MAXIM [Maxim Integrated Products]

Low-Noise, Regulated, Negative
Charge-Pump Power Supplies for GaAsFET Bias
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.
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
3) Use a ground plane.
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.
________________________________________________________Package Information
8
and capacitance. This includes connections to FB.
______________________________________________________________________________________
e
Noise and Ripple Measurement
D
B
A1
Layout and Grounding
E
A
H
0.127mm
0.004in.
C
h x 45˚
TRANSISTOR COUNT: 164
SUBSTRATE CONNECTED TO IN
___________________Chip Topography
NEGOUT
L
C1+
C1-
SHDN (MAX850/853)
SHDN (MAX851)
OSC (MAX852)
(2.159mm)
0.085"
DIM
A1
C
D
H
A
B
E
e
h
L
0.053
0.004
0.014
0.007
0.189
0.150
0.228
0.010
0.016
SMALL-OUTLINE
MIN
0˚
8-PIN PLASTIC
0.050 BSC
INCHES
PACKAGE
0.069
0.010
0.019
0.010
0.197
0.157
0.244
0.020
0.050
MAX
8˚
IN
GND
FB (MAX850–852)
CONT (MAX853)
OUT
MILLIMETERS
1.35
0.10
0.35
0.19
4.80
3.80
5.80
0.25
0.40
MIN
0˚
1.27 BSC
(3.226mm)
0.127"
MAX
21-325A
1.75
0.25
0.49
0.25
5.00
4.00
6.20
0.50
1.27
8˚