Datasheet

18
LT1790
1790fa
APPLICATIONS INFORMATION
WUU
U
Bypass and Load Capacitors
The LT1790 voltage references should have an input
bypass capacitor of 0.1µF or larger, however the bypass-
ing of other local devices may serve as the required
component. These references also require an output ca-
pacitor for stability. The optimum output capacitance for
most applications is 1µF, although larger values work as
well. This capacitor affects the turn-on and settling time
for the output to reach its final value.
All LT1790 voltages perform virtually the same, so the
LT1790-2.5 is used as an example.
Figure 1 shows the turn-on time for the LT1790-2.5 with
a 1µF input bypass and 1µF load capacitor. Figure 2 shows
the output response to a 0.5V transient on V
IN
with the
same capacitors.
The test circuit of Figure 3 is used to measure the stability
of various load currents. With R
L
= 1k, the 1V step
produces a current step of 1mA. Figure 4 shows the
response to a ±0.5mA load. Figure 5 is the output re-
sponse to a sourcing step from 4mA to 5mA, and Figure␣ 6
is the output response of a sinking step from –4mA to
–5mA.
Figure 1. Turn-On Characteristics of LT1790-2.5
3V
2V
1V
0V
V
IN
V
OUT
1790 F01
Figure 2. Output Response to 0.5V Ripple on V
IN
3V
2V
1V
0V
V
IN
V
OUT
1790 F02
Figure 3. Response Time Test Circuit
Figure 4. LT1790-2.5 Sourcing and Sinking 0.5mA
3V
2V
V
GEN
V
OUT
(AC COUPLED)
1790 F04
Figure 5. LT1790-2.5 Sourcing 4mA to 5mA
–3V
–2V
V
GEN
V
OUT
(AC Coupled)
1790 F05
LT1790-2.5
C
IN
0.1µF
C
L
1µF
V
GEN
1790 F03
1V
V
IN
3V
4
1, 2
1k
6