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LM2696

SNVS375B – OCTOBER 2005 – REVISED APRIL 2013

www.ti.com

FEEDBACK RESISTORS

The feedback resistors are used to scale the output voltage to the internal reference value such that the loop can

be regulated. The feedback resistors should not be made arbitrarily large as this creates a high impedance node

Where

•

typical).

(12)

The output voltage value can be set in a precise manner by taking into account the fact that the reference

voltage is regulating the bottom of the output ripple as opposed to the average value. This relationship is shown

in Figure 19.

Figure 19. Average and Ripple Output Voltages

It can be seen that the average output voltage is higher than the gained up reference by exactly half the output

term may be expressed using the relationship:

(13)

One should note that for high output voltages (>5V), a load of approximately 15 mA may be required for the

output voltage to reach the desired value.

INPUT CAPACITOR

according to the load current. In general, package size and ESR determine the current capacity of a capacitor. If

these criteria are met, there should be enough capacitance to prevent impedance interactions with the source. In

general, it is recommended to use a low ESR, high capacitance electrolytic and ceramic capacitor in parallel.

Using two capacitors in parallel ensures adequate capacitance and low ESR over the operating range. The

Sanyo MV-WX series electrolytic capacitors and a ceramic capacitor with X5R or X7R dielectric are an excellent

combination. To calculate the input capacitor RMS, one may use the following relationship:

(14)

that can be approximated by,

(15)

Typical values are 470 µF for the electrolytic capacitor and 0.1 µF for the ceramic capacitor.

12

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