LT6650

8

6650f

operated from a small battery or other relatively high

impedance source, a minimum 1

µF 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 22

µF) 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

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 1

the output settles in approximately 0.5ms. Figure 4 shows

APPLICATIO S I FOR ATIO

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

(100

µA to –100µA)

Figure 6. Output Response to Current-Sourcing Load Step

(–100

µA to –200µA)

4.7k

NOISY

POWER BUS

6650 F02

22

µF

1N751

5V

33k

1

µF

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 –100

µA and –200µA in Figure 6; and sinkingcurrent

6650 F05

10mV/DIV

SINKING

SOURCING

100

µA

SINKING

100

µA

SOURCING

6650 F06

10mV/DIV

AC

–100

µA

–200

µA

0.2ms/DIV

6650 F03

3V

0V

0.4V

0V

2ms/DIV

6650 F04

3V

2.5V

0.4V

0V