LM1770

SNVS403C – SEPTEMBER 2005 – REVISED APRIL 2013

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JITTER

The LM1770 utilizes a constant on-time control scheme that relies on the output voltage ripple to provide a

consistent switching frequency. Under certain conditions, excessive noise can couple onto the feedback pin

causing the switch node to appear to have a slight amount of jitter. This is not indicative of an unstable design.

The output voltage will still regulate to the exact same value. Careful component selection and layout should

minimize any external influence.

In addition to any external noise that can add to the jitter seen on the switch node, the LM1770 will always have

a slight amount of switch jitter. This is because the LM1770 makes a small alteration in the reference voltage

every 128 cycles to improve its accuracy and long term performance. This has the effect of causing a change in

the switching frequency at that instant. When viewed on an oscilloscope this can be seen as a jitter in the switch

node. The change in feedback voltage or output voltage, however, is almost indistinguishable.

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