LP4950C-5V, LP4951C

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SNVS208C – SEPTEMBER 2002 – REVISED APRIL 2013

*See Application Hints

.

. **Drive with TTL-high to shut down. Ground or leave open if shutdown feature is not to be used.

.

Note: Pins 2 and 6 are left open.

Figure 37. Adjustable Regulator (LP4951C)

REDUCING OUTPUT NOISE

In reference applications it may be advantageous to reduce the AC noise present at the output. One method is to

reduce the regulator bandwidth by increasing the size of the output capacitor. This is the only way noise can be

reduced on the 3 lead LP4950C but is relatively inefficient, as increasing the capacitor from 1

μF to 220μF only

decreases the noise from 430

μV to 160μV rms for a 100kHz bandwidth at 5V output.

Noise can be reduced fourfold by a bypass capacitor across R1, since it reduces the high frequency gain from 4

to unity. Pick

(2)

or about 0.01

μF. When doing this, the output capacitor must be increased to 3.3μF to maintain stability. These

changes reduce the output noise from 430

μV to 100μV rms for a 100kHz bandwidth at 5V output. With the

bypass capacitor added, noise no longer scales with output voltage so that improvements are more dramatic at

higher output voltages.

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Product Folder Links: LP4950C-5V LP4951C