VPP supply max686

[tridentsx]

I am collecting ideas for how to design an universal programmer.

My goal is to feed it 5v from USB without the need for additional power feed.
The VPP needs to be variable 5v to 25v hence I need some type of boost regulator.

How close to the device rated VPP does the VPP actually have to be ? For example if a device needs 12.2v VPP for programming would 12.5v or 12v work? What is normally the current draw from the VPP supply when programming a device?

I am thinking that I could use a MAX686 to generate the VPP and to control the voltage of VPP ? my concerns are if the voltage granularity is enough and if the current is enough ?
 
http://www.maximintegrated.com/datasheet/index.mvp/id/1817/t/al

[c4757p]

How close to the device rated VPP does the VPP actually have to be ? For example if a device needs 12.2v VPP for programming would 12.5v or 12v work? What is normally the current draw from the VPP supply when programming a device?

You're going to have to check the datasheets. For example, the PIC18FXx20 wants 9.0 - 13.25V and draws 300 uA. I found this in the separate reference, "Flash Microcontroller Programming Specification", available on their website. I'd imagine this is similar across the line. Personally I'd aim for no worse than ±5% if you're going to try to make a "universal" programmer.

[c4757p]

That is an expensive chip. For a bit less you could do this with two PWM outputs on a microcontroller: use one to drive a discrete boost converter at a fixed but unregulated voltage. Run an op amp off this voltage, configured as a noninverting amplifier, then put the other PWM through a low-pass filter into the op amp. Even better, skip the boost converter - just use around 24VDC as the main power supply for the programmer.

[Alana]

From my observations of atmel 89c51 chips that i played with long time ago anything lower than 11.5V on VPP was not enough to program them. I wanted to power my DIY programer and project from the same PC PSU but eventually i ended up with separate PSUs - small 100mA 12VDC unregulated for programmer and PC PSU for project. Those unregulated psus have peak voltage of 14-17V and that was enough for my programer to work correctly.

c4757p - you are refering to pickit2 schematic?

[c4757p]

No, I'm referring to this.