Re: Driving a CMOS driver when VDD is not present
- From: Winfield Hill <Winfield_member@xxxxxxxxxxx>
- Date: 3 Nov 2006 04:04:39 -0800
Kam wrote...
I need to drive 10 Microchip TC4432 high voltage drivers
(http://ww1.microchip.com/downloads/en/DeviceDoc/21424c.pdf) from
3.3V logic (Xilinx Spartan 3). Each of the 10 TC4432 is driven by
an independent signal.
The VDD of the TC4432 is normally at +24V level. The problem is that
the +24V that powers the TC4432 and the +3.3V that powers the logic
are from different power supplys which can be switched on and off
independelty. As a result, the +3.3V logic may drive the TC4432
while the VDD of the TC4432 is at zero level.
This will violate the absolute max input voltage of the TC4432
which is specified as VDD + 0.3V.
Is it safe to drive the TC4432 through a current limiting resistor
(e.g. 1K) and relay on the internal parasitic diode at the TC4432
input to limit the input voltage?
I'd use the 1k resistor solution if I were you. The '4432 will
be powered from the logic inputs via the protection diode, but
the logic current will be low at 3.3-0.6 = 2.7V, and the '4432
will be disabled by its under-voltage lockout. The protection
diode design is meant to handle high currents without causing
bad chip behavior, such a supply latchup, but it's a good idea
to limit the current with a 1k resistor anyway.
--
Thanks,
- Win
.
- References:
- Prev by Date: Re: Anyone here know how an one-armed bandit (slot machine) works?
- Next by Date: SMD thick film resistors with exposed film path?
- Previous by thread: Driving a CMOS driver when VDD is not present
- Next by thread: Re: Driving a CMOS driver when VDD is not present
- Index(es):
Relevant Pages
|
