DIY Quad Charge-pump for high side n-mofet drive

tonyp12

At 18 cents each (IC) not to expensive to make.
http://www.mouser.com/Semiconductors/Logic-ICs/Buffers-Line-Drivers/_/N-50nahZscv7?P=1z0z7ptZ1z0slkvZ1z0sqwkZ1z0y3j8Z1z0yhi1Z1yzsrje&Keyword=ABT&FS=True&Ns=Pricing|0

I wanted to make so a high Prop pin = N-Channel mosfet ON, I ended up with this config.

If you are OK with the reversed, a hex open drain HCT05 would be OK instead of a ABT125 and use the ABT125 for charge pump.
plus it leaves you two pins extra for something else.
Or even a ULN2003, that give you an extra 3 pins.

I have not tested it. 200pF could be higher like 1nF etc

Maybe need a voltage tripler, if your VGS is not happy with 4v.
Picture is showing 1/4 of output stage.
dual-dual-series Schottky diodes and 4x array Caps make for less parts.

If you only have 3.3V available, you could use LVC versions and boost 3.3 to 6V (but is only a 2.7v highside VGS)

jmg

tonyp12 wrote: »

I wanted to make so a high Prop pin = N-Channel mosfet ON, I ended up with this config.

That Voh is getting tough on the ABT125...

The better Hi side drivers include low drive lockout, as you do not really want too slow a turn-on with low impedance loads.

P-FETS are getting cheaper, and lower Rds, and they avoid the need for any charge Pump.
eg the AON6403 comes at 30V and 4.3mOhms

Phil Pilgrim (PhiPi)

jmg wrote:

P-FETS are getting cheaper, and lower Rds, and they avoid the need for any charge Pump.

True, but you still need to drive the gate to Vin to turn it off; so there's still some external circuitry involved to interface with logic-level signals.

Despite the slow turn-on resulting from starting and stopping the charge pump, I think Tony's idea could enjoy some traction where cost is the overriding concern. My gut tells me that 200pF may be on the low side with a 100 kHz drive. OTOH, you don''t want to slow down the start-up more than you have to.

-Phil

Duane C. Johnson

Phil Pilgrim (PhiPi) wrote: »

Despite the slow turn-on resulting from starting and stopping the charge pump, I think Tony's idea could enjoy some traction where cost is the overriding concern. My gut tells me that 200pF may be on the low side with a 100 kHz drive. OTOH, you don''t want to slow down the start-up more than you have to.

Back of the envelope calculation;
My favorite IRF3708 MOSFET.
Gate Charge = 24nC
Drive amplitude = 5V
Drive frequency = 100KHz
C1 = 200pF

5V * 200pF = 1nC C1 charge transfer per cycle
24nC / 1nC = 24 cycles to charge the gate.
24 / 100_000Hz = 240uS

Quite workable if it's not switched to fast.

Raise the frequency to 1MHz and make C1 = 1nF then the gate charge time would be 5uS.
Seems a lot better.

Actually the switching time will be quite a bit faster.
Clearly this is not a rigorous calculation but probably in the ball park.

Duane J

tonyp12

Two of these dual N-mosfet (low gate charge)
http://www.mouser.com/ProductDetail/ON-Semiconductor/NUD3105DMT1G/?qs=sGAEpiMZZMsrr1kXJis%252bJ9gC9QYtqlpBYnbkRShrNLY%3d
(though having these on highside is not good for pull-down resistor or zeners?)

and two of a double dual-serias diodes:
http://www.mouser.com/ProductDetail/Diodes-Inc/SD103ASDM-7-F/?qs=sGAEpiMZZMuIUjt4yeP9c0AkDE5kF2Il%2fbaifs6KGd8%3d

and finally two 4 element array (pick your choice of pF):
http://www.mouser.com/Passive-Components/Capacitors/Ceramic-Capacitors/Capacitor-Arrays-Networks/_/N-5g91Zscv7?P=1z0x8hsZ1z0x7p2Z1z0x74kZ1z0x7weZ1z0x75aZ1z0t6fgZ1z0vhw8Z1z0vkpmZ1z0wpq0Z1yzh20z&Ns=Pricing%7c0

And a quad high-side relay driver is done.
Is it worth it?, maybe, there are probably ICs out there that does this for you.

Parts was selected on pin spacing , 0.65mm was weeded out as that is for more advanced smt solderers.