I would like to confirm off-pulse skipping operation.
I understand off-pulse skipping operate when the input voltage is falling down and approaches the nominal output voltage.
Is this correct?
And when off-pulse skipping operate and the input voltage falls down moreover, how do LM26001 operate?
And when does LM26001 stop the switching operation and operate such as figure 14 (output voltage = Input voltage - Iout * (RDS(ON) + LDCR))?
Best regards,
Atsushi Yamauchi
Hello Yamauchi-san,
Yes, you're correct: off-pulse skipping operation occurs when the input voltage falls and approaches the nominal output voltage.
Page 14 of the LM26001-Q1 datasheet provides the following description of Off-Pulse Skipping operation:
"If the input voltage approaches the nominal output voltage, the duty cycle is maximized to hold up the output
voltage. In this mode of operation, once the duty cycle reaches its maximum, the LM26001 can skip a maximum
of seven off pulses, effectively increasing the duty cycle and thus minimizing the dropout from input to output."
Figure 20 of the datasheet shows an example of this operation:
A quick way of calculating the minimum VIN that can be set before the start of pulse skipping operation:
VIN_min = VOUT / [Efficiency x (1- (Fsw x Off-time) ) ] , where: Off-time is 365 ns (typ) from LM26001-Q1 electrical table of datasheet
As the VIN keeps dropping you'll eventually get to the dropout operation listed on Figure 14, where the output voltage will be set by the IR drop listed by your equation.
Best Regards,
-Juan
