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Highside FET extending on time indefinitely

This is from AN978 pg18 using IR's bootstrapped HS drivers.

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You can see from the picture they have the timer tied to ground through a 100k resistor why not just use the HS driver's 12Vdc return? Is there any reason this wouldn't work with the 555 ground tied to the same return as the IR2125.

I'm trying to do something similar keep a HS Fet on for extended periods. I'm using a FAN7361 HS driver. I have a PIC operating off the same 16VDc supply that the driver is operating off through a 5V shunt. Could I use one of the PIC's outputs to recharge the boost cap in the FAN7361 driver so it can keep the FET on until the PIC tells it to shutdown?

FAN7361 data sheet

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AN978 (pg18)

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Reply to
Hammy
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Hi Hammy,

as far as i'm concerned, they are tied to the same ground. the reason there's a 100k resistor is because they need to limit the current trough that zener diode. the zener diode is used to clamp the input voltage for the timer power supply to 14.4V. but you need to limit the break down current on that diode other wise it will blow. the 100k resistor is doing that.

for the second point, no, you need higher voltage then the source to keep the FET on. so i would suggest a charge pump IC to do it.

what type of application are you trying to achieve? what's the voltage on the rail? maybe you are using the wrong part. this is the high speed switching driver, but not the ON and OFF control switch.

Reply to
tomrei

Yes maybe I'll look at mechanical relays again.

Reply to
Hammy

well, i know some part maybe can help, that's why i asked what's the voltage on the rail you plan to control...

the ADM4210 can act as a switch, it's a hotswap controller used to protect the circuit by current limiting the inrush current when you hot plug power. it has build in charge pumps used to control the external FET in turn control the rail. if you want to limit the current and do some protection, use the sense resistor. if you don't need that and just want a logic controlled switch, then just short the Vcc and sense pin, tied the timer pin to high and use the ON pin to control the on and off of the FET. beware this part can only operate to maximum of 16.5V rails. for higher rail, you may need to control the low side instead.

hope it helps

yours Ren

Reply to
tomrei

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