Datasheet

14
LT1218/LT1219
APPLICATIONS INFORMATION
WUU
U
compensation. The output capacitance forms a filter,
which reduces pickup from the supply and lowers the
output impedance. This additional filtering is helpful in
mixed analog/digital systems with common supplies or
systems employing switching supplies. Filtering also
reduces high frequency noise, which may be beneficial
when driving A/D converters.
Figures 7a and 7b show the outputs of the LT1218/LT1219
perturbed by a 200mV
P-P
50kHz square wave added to the
positive supply. The LT1219 power supply rejection is
about ten times greater than that of the LT1218 at 50kHz.
Note the 5-to-1 scale change in the output voltage traces.
The tolerance of the external compensation capacitor is
not critical. The plots of Overshoot vs Load Current in the
Typical Performance Characteristics section illustrate the
effect of a capacitive load.
LT1218/19 • F07a
Figure 7a. LT1218 Power Supply Rejection Test
LT1218/19 • F07b
Figure 7b. LT1219 Power Supply Rejection Test
TYPICAL APPLICATIONS
U
Buffer for 12-Bit A/D Converter
V
REF

+IN
–IN
GND
V
CC

CLK
D
OUT
CS/SHDN
1
2
3
4
8
7
6
5
LTC1285
–
+
TO µP
1µF
0.1µF
0.1µF
3V
V
IN
LT1219
LT1218/19 • TA03
High-Side Current Source
–
+
LT1218
1k
R
SENSE
0.2Ω
40k
Q1
MTP23P06
I
LOAD
5V < V
CC
< 30V
0A < I
LOAD
< 1A AT V
CC
= 5V
0mA < I
LOAD
< 160mA AT V
CC
= 30V

Q2
2N4340
V
CC
100Ω
0.0033µF
LT1004-1.2
R
P

10k
LT1218/19 • TA04
V
+
(AC)
V
OUT
V
+
(AC)
V
OUT