On Friday, January 25, 2013 3:49:45 AM UTC+13, Allan Herriman wrote:
> Hi,
> 
> I'm looking for a shift register to do some output expansion to drive 
> LEDs, small relays, etc.


Something like ?
http://www.ti.com/product/tca6408a

Or, there are CPLDs with 3.3V io and 1.8V cores 

If you google IO expander they tend to have more level shifting smarts, than shift registers.
-jg

Allan Herriman wrote:

> Hi,
> 
> I'm looking for a shift register to do some output expansion to drive
> LEDs, small relays, etc.
> 
> I'd like to use something akin to the 74xx595 which has a serial input
> and 8 outputs.
> 
> Good so far.
> 
> I need to use a shift register with either open drain outputs, or outputs
> that can drive at least 3.3V (high or low, I don't mind).  The current
> will be up to a few tens of mA.  I don't mind if I have to parallel a few
> outputs to get that.
> 
> My problem is that the device that will be controlling the shift register
> has 1.8V outputs.
> I can't find any shift register devices that can work with 1.8V inputs,
> whilst meeting my output requirements.
> All the ones I can find seem to have a Vih min of 2.0V, which won't work
> reliably when driven with a 1.8V signal.
> 
> I could easily design a level converter to go from 1.8V to 3.3, but I was
> hoping to find a single device that could do what I want.
> 
> Any ideas?

You need a level shifter to interface between the controlling device and 
your output device. A quick Google on the term "level shifter" should find 
plenty of hits.

-- 
********************************************************************
Paul E. Bennett...............<email://Paul_E.Bennett@topmail.co.uk>
Forth based HIDECS Consultancy
Mob: +44 (0)7811-639972
Tel: +44 (0)1235-510979
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On Thu, 24 Jan 2013 14:49:45 +0000, Allan Herriman wrote:

> Hi,
> 
> I'm looking for a shift register to do some output expansion to drive
> LEDs, small relays, etc.
> 
> I'd like to use something akin to the 74xx595 which has a serial input
> and 8 outputs.
> 
> Good so far.
> 
> I need to use a shift register with either open drain outputs, or
> outputs that can drive at least 3.3V (high or low, I don't mind).  The
> current will be up to a few tens of mA.  I don't mind if I have to
> parallel a few outputs to get that.
> 
> My problem is that the device that will be controlling the shift
> register has 1.8V outputs.
> I can't find any shift register devices that can work with 1.8V inputs,
> whilst meeting my output requirements. All the ones I can find seem to
> have a Vih min of 2.0V, which won't work reliably when driven with a
> 1.8V signal.
> 
> I could easily design a level converter to go from 1.8V to 3.3, but I
> was hoping to find a single device that could do what I want.

It's not getting you all the way, but -- surely there are TinyLogic 
buffers that'll hear 1.8V and talk 3.3.  You'll need what -- three?  
Clock, data, and latch or enable?  That should be possible in two itty 
bitty packages.

-- 
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

On Thu, 24 Jan 2013 14:49:45 +0000, Allan Herriman wrote:

> Hi,
> 
> I'm looking for a shift register to do some output expansion to drive
> LEDs, small relays, etc.
> 
> I'd like to use something akin to the 74xx595 which has a serial input
> and 8 outputs.
> 
> Good so far.
> 
> I need to use a shift register with either open drain outputs, or
> outputs that can drive at least 3.3V (high or low, I don't mind).  The
> current will be up to a few tens of mA.  I don't mind if I have to
> parallel a few outputs to get that.
> 
> My problem is that the device that will be controlling the shift
> register has 1.8V outputs.
> I can't find any shift register devices that can work with 1.8V inputs,
> whilst meeting my output requirements.
> All the ones I can find seem to have a Vih min of 2.0V, which won't work
> reliably when driven with a 1.8V signal.
> 
> I could easily design a level converter to go from 1.8V to 3.3, but I
> was hoping to find a single device that could do what I want.
> 
> Any ideas?


I just found the NLSF595 from On Semi.  It has open drain outputs, but is 
only specified at 50uA output current with a 2.0V supply.  At 3.3V its 
output drive is fine, but I lose the 1.8V input compatibility.

Allan

Hi,

I'm looking for a shift register to do some output expansion to drive 
LEDs, small relays, etc.

I'd like to use something akin to the 74xx595 which has a serial input 
and 8 outputs.

Good so far.

I need to use a shift register with either open drain outputs, or outputs 
that can drive at least 3.3V (high or low, I don't mind).  The current 
will be up to a few tens of mA.  I don't mind if I have to parallel a few 
outputs to get that.

My problem is that the device that will be controlling the shift register 
has 1.8V outputs.
I can't find any shift register devices that can work with 1.8V inputs, 
whilst meeting my output requirements.
All the ones I can find seem to have a Vih min of 2.0V, which won't work 
reliably when driven with a 1.8V signal.

I could easily design a level converter to go from 1.8V to 3.3, but I was 
hoping to find a single device that could do what I want.

Any ideas?

Thanks,
Allan