Chip to turn on/off various circuits

Hi all,

I have a battery powered device that has three exclusive circuits, and
to save power I want to be able to control which circuits are on. Can
anyone recommend a chip or point me in the right direction to an IC that
can be used to control the power to up to 4 circuits. Currently I'm
using a couple of PNP transistors but I would like to free up some I/O
ports on the PIC.

Thanks
Ross

On Thu, 04 May 2006 08:33:13 +1000, in comp.arch.embedded Ross
Marchant <> wrote:

>Hi all,
>
>I have a battery powered device that has three exclusive circuits, and
>to save power I want to be able to control which circuits are on. Can
>anyone recommend a chip or point me in the right direction to an IC that
>can be used to control the power to up to 4 circuits. Currently I'm
>using a couple of PNP transistors but I would like to free up some I/O
>ports on the PIC.
>
>Thanks
>Ross
7HC138 ?


martin

martin griffith wrote:
> On Thu, 04 May 2006 08:33:13 +1000, in comp.arch.embedded Ross
> Marchant <> wrote:
>
>> Hi all,
>>
>> I have a battery powered device that has three exclusive circuits, and
>> to save power I want to be able to control which circuits are on. Can
>> anyone recommend a chip or point me in the right direction to an IC that
>> can be used to control the power to up to 4 circuits. Currently I'm
>> using a couple of PNP transistors but I would like to free up some I/O
>> ports on the PIC.
>>
>> Thanks
>> Ross
> 7HC138 ?
>
>
> martin

Sorry - forgot to mention that it has to supply up to 100mA @ 5V

Ross

Then a 74HC138 + PChan FETS

James

"martin griffith" <> wrote in message
news:...
> On Thu, 04 May 2006 08:33:13 +1000, in comp.arch.embedded Ross
> Marchant <> wrote:
>
>>Hi all,
>>
>>I have a battery powered device that has three exclusive circuits, and
>>to save power I want to be able to control which circuits are on. Can
>>anyone recommend a chip or point me in the right direction to an IC that
>>can be used to control the power to up to 4 circuits. Currently I'm
>>using a couple of PNP transistors but I would like to free up some I/O
>>ports on the PIC.
>>
>>Thanks
>>Ross
> 7HC138 ?

Two possibilities here:
- either the "7HC138" (with no 4, so not 74HC) is some kind of power
controller I don't know about (Google did throw up a few links, but from
their context, they *look* like typos)
- or you're talking about the 74HC138, which is a one-of-eight decoder
(with enables). Which makes no sense. It's not a latch, and is not a power
driver.

So: huh?

Steve
http://www.fivetrees.com

"Steve at fivetrees" <> wrote in message
news:...
> "martin griffith" <> wrote in message
> news:...
>> On Thu, 04 May 2006 08:33:13 +1000, in comp.arch.embedded Ross
>> Marchant <> wrote:
>>
>>>I have a battery powered device that has three exclusive circuits, and
>>>to save power I want to be able to control which circuits are on. Can
>>>anyone recommend a chip or point me in the right direction to an IC that
>>>can be used to control the power to up to 4 circuits. Currently I'm
>>>using a couple of PNP transistors but I would like to free up some I/O
>>>ports on the PIC.
>>
>> 7HC138 ?
>
> Two possibilities here:
> - either the "7HC138" (with no 4, so not 74HC) is some kind of power
> controller I don't know about (Google did throw up a few links, but from
> their context, they *look* like typos)
> - or you're talking about the 74HC138, which is a one-of-eight decoder
> (with enables). Which makes no sense. It's not a latch, and is not a power
> driver.

Re-reading that carefully (as one sometimes does *after* one presses the
"send" key):

>> I have a battery powered device that has three exclusive circuits, and
>> to save power I want to be able to control which circuits are on.

Ah. If the OP really means "exclusive" in the sense of "only one at a time"
(I'd taken "I want to be able to control which circuits are on" rather more
literally), then I see your point. However, he'd still need 3 control lines
(2 address, 1 enable), as opposed to 4.

Steve
http://www.fivetrees.com

On Thu, 04 May 2006 08:33:13 +1000, the renowned Ross Marchant
<> wrote:

>Hi all,
>
>I have a battery powered device that has three exclusive circuits, and
>to save power I want to be able to control which circuits are on. Can
>anyone recommend a chip or point me in the right direction to an IC that
>can be used to control the power to up to 4 circuits. Currently I'm
>using a couple of PNP transistors but I would like to free up some I/O
>ports on the PIC.
>
>Thanks
>Ross

If you can switch the low side, TI has some nice DMOS open-drain power
shift registers that allow you to switch 8 lines per chip using a few
port pins. Essentially an HC595 with a N-channel MOSFET on each Q
output.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

Steve at fivetrees wrote:
> "Steve at fivetrees" <> wrote in message
> news:...
>> "martin griffith" <> wrote in message
>> news:...
>>> On Thu, 04 May 2006 08:33:13 +1000, in comp.arch.embedded Ross
>>> Marchant <> wrote:
>>>
>>>> I have a battery powered device that has three exclusive circuits, and
>>>> to save power I want to be able to control which circuits are on. Can
>>>> anyone recommend a chip or point me in the right direction to an IC that
>>>> can be used to control the power to up to 4 circuits. Currently I'm
>>>> using a couple of PNP transistors but I would like to free up some I/O
>>>> ports on the PIC.
>>> 7HC138 ?
>> Two possibilities here:
>> - either the "7HC138" (with no 4, so not 74HC) is some kind of power
>> controller I don't know about (Google did throw up a few links, but from
>> their context, they *look* like typos)
>> - or you're talking about the 74HC138, which is a one-of-eight decoder
>> (with enables). Which makes no sense. It's not a latch, and is not a power
>> driver.
>
> Re-reading that carefully (as one sometimes does *after* one presses the
> "send" key):
>
>>> I have a battery powered device that has three exclusive circuits, and
>>> to save power I want to be able to control which circuits are on.
>
> Ah. If the OP really means "exclusive" in the sense of "only one at a time"
> (I'd taken "I want to be able to control which circuits are on" rather more
> literally), then I see your point. However, he'd still need 3 control lines
> (2 address, 1 enable), as opposed to 4.
>
> Steve
> http://www.fivetrees.com
>
>

Thanks for all the replies.

Sorry, I should have said "control which circuit is on".

I have solved the problem anyway - I've put an extra latch on my portb
bus and am using that to control the shutdown pins on a few LP2985 LDO
regulators.

Thanks all,
Ross

Ross Marchant scrobe on the papyrus:

> Hi all,
>
> I have a battery powered device that has three exclusive circuits,
> and to save power I want to be able to control which circuits are on.
> Can anyone recommend a chip or point me in the right direction to an
> IC that can be used to control the power to up to 4 circuits.
> Currently I'm using a couple of PNP transistors but I would like to
> free up some I/O ports on the PIC.
>
> Thanks
> Ross

Look at the Allegro UDN2987 or for an addressable latched version the
A6259.

http://www.allegromicro.com/


--
John B