Datasheet

LT6650
8
6650fa
operated from a small battery or other relatively high
impedance source, a minimum 1µF capacitor is recom-
mended. PSRR can be significantly enhanced by adding a
low-pass RC filter on the input, with a time-constant of
1ms or higher, as shown in Figure 1. The Typical Perfor-
mance Characteristics graphs show performance as a
function of several combinations of input and output
capacitance.
An input RC of 100ms or more is recommended (such as
5k and 22µF) when output transients must be minimized
in the face of high supply noise, such as in automotive
applications. Figure 2 shows an input filter structure that
effectively eliminates supply transients from affecting the
output. With this extra input decoupling and the LT6650
operating normally from a 12V bus, 50V transients induce
less than <0.5% V
OUT
perturbations.
Figure 3 shows the turn-on response time for the circuit in
Figure 1. The input voltage steps from 0V to 3V, and the
output is configured to produce 400mV. Input bypass and
output load capacitance are 1µF, R
IN
= 0Ω, R
Z
= 0Ω, and
the output settles in approximately 0.5ms. Figure 4 shows
APPLICATIO S I FOR ATIO
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Figure 2. High Noise-Immunity Input Network
Figure 3. LT6650 Turn-On Characteristic
Figure 4. Output Response to ±0.5V Input Step
Figure 5. Output Response to Bidirectional Load Step
(100µA to –100µA)
Figure 6. Output Response to Current-Sourcing Load Step
(–100µA to –200µA)
V
IN
4.7k
NOISY
POWER BUS
6650 F02
22µF
1N751
5V
33k
1µF
the same circuit responding to input transients of 0.5V,
settling in about 0.3ms. Figures 5 through 7 show the
same circuit responding to various load steps: changes
between ±100µA in Figure 5; sourcing current step be-
tween –100µA and –200µA in Figure 6; and sinking current
6650 F05
V
OUT
10mV/DIV
I
OUT
SINKING
SOURCING
100µA
SINKING
100µA
SOURCING
6650 F06
V
OUT
10mV/DIV
AC
I
OUT
–100µA
–200µA
V
OUT
0.2ms/DIV 6650 F03
V
IN
3V
0V
0.4V
0V
2ms/DIV
6650 F04
V
IN
V
OUT
3V
2.5V
0.4V
0V