SW

ON

OUT

IN

f

t

V

V

˜

d

15

LM60440, LM60430

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SNVSBN5A – FEBRUARY 2020 – REVISED JUNE 2020

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Device Functional Modes (continued)

8.4.3 Minimum Switch On-Time

Every switching regulator has a minimum controllable on-time dictated by the inherent delays and blanking times

associated with the control circuits. This imposes a minimum switch duty cycle and, therefore, a minimum

conversion ratio. The constraint is encountered at high input voltages and low output voltages. To help extend

the minimum controllable duty cycle, the LM604x0 automatically reduces the switching frequency when the

minimum on-time limit is reached. This way the converter can regulate the lowest programmable output voltage

at the maximum input voltage. An estimate for the approximate input voltage, for a given output voltage, before

Characteristics table. As the input voltage is increased, the switch on-time (duty-cycle) reduces to regulate the

output voltage. When the on-time reaches the limit, the switching frequency drops, while the on-time remains

fixed.

(2)