Datasheet LT6650 (Analog Devices) - 8

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