alternative of LTC6992?

You could make something out of cheap parts... depends on your exact needs.

Yikes! $5 in onesies, $3 in reels for a glorified RC monostable?

Such as an NE556D dual timer, with one side being an astable and the other side a monostable with a variable threshold. Ten cents in any quantity, direct from TI.

A bit more design is required, of course--you have to take account of the tolerances of the chip and timing components, especially if you want to get duty cycles near 0.

OTOH if the OP uses a resistor to a higher supply rail (and a diode to V+ for protection), the ramp will linearize pretty well. Extra points for using a BJT current source. ;)

Cheers

Phil Hobbs

Single chip microcontrollers can do the same job. You need an internal clock that runs faster than 1MHz to get the same frequency range, but some run up to 100MHz and faster (though they tend to be bit greedy with supply current).

Depends on what you want to do. Check Octopart:

About the simplest voltage to duty cycle converter is a schmitt gate oscillator and one added resistor. Real cheapskates can delete the cap.

Fancier, use a dial opamp or comparator as a triangle oscillator + comparator.

If Piyush can give us some details of the requirements, we could design something with him. Group design is fun.

Yeah, if the rep rate doesn't need to be constant you can do without a lot of stuff. Simplifies the tolerances too.

Cheers

Phil Hobbs

Schmitt gate inverter, one resistor, one thermistor. It's a PWM temperature controller!

For sufficiently permissive definitions of 'controller'. ;0

(It would be fairly challenging without at least one other resistor for heating, unless you're just trying to control the temperature of the thermistor.)

Cheers

Phil Hobbs

It would drive a mosfet or an SSR or something.