I've never used a 3.x Volt device before. I see the LPC2148 has "5V
Tolerant" IO pins.
Can I use them as I would the pins on a 5V device or are there things I
must be aware of ?
As far as the ADC is concerned, the manual says:
"• Measurement range 0 V to VREF (typically 3 V; not to exceed VDDA
voltage level)."
I need to interface to a device that has a 1 to 5V analog output. Is
there an easy way to use the LPC2148's 0 to 3V ADC to convert this ? A
resistor divider comes to mind. Is there a better way ?
Thanks.
5V tolerant pin tips ? 5V ADC VREF ?
Started by ●March 12, 2007
Reply by ●March 12, 20072007-03-12
A resistor divider is one way, or just use an external ADC.
There are plenty of SPI and I2C connected ADC chips out there.
Baldur
On Mon, Mar 12, 2007 at 03:06:25PM -0600, armdeveloper wrote:
> I've never used a 3.x Volt device before. I see the LPC2148 has "5V
> Tolerant" IO pins.
>
> Can I use them as I would the pins on a 5V device or are there things I
> must be aware of ?
>
> As far as the ADC is concerned, the manual says:
> "??? Measurement range 0 V to VREF (typically 3 V; not to exceed VDDA
> voltage level)."
>
> I need to interface to a device that has a 1 to 5V analog output. Is
> there an easy way to use the LPC2148's 0 to 3V ADC to convert this ? A
> resistor divider comes to mind. Is there a better way ?
>
> Thanks.
>
> Yahoo! Groups Links
There are plenty of SPI and I2C connected ADC chips out there.
Baldur
On Mon, Mar 12, 2007 at 03:06:25PM -0600, armdeveloper wrote:
> I've never used a 3.x Volt device before. I see the LPC2148 has "5V
> Tolerant" IO pins.
>
> Can I use them as I would the pins on a 5V device or are there things I
> must be aware of ?
>
> As far as the ADC is concerned, the manual says:
> "??? Measurement range 0 V to VREF (typically 3 V; not to exceed VDDA
> voltage level)."
>
> I need to interface to a device that has a 1 to 5V analog output. Is
> there an easy way to use the LPC2148's 0 to 3V ADC to convert this ? A
> resistor divider comes to mind. Is there a better way ?
>
> Thanks.
>
> Yahoo! Groups Links
Reply by ●March 12, 20072007-03-12
---- Original Message ----
From: "armdeveloper"
To:
Sent: Monday, March 12, 2007 10:06 PM
Subject: [lpc2000] 5V tolerant pin tips ? 5V ADC VREF ?
> I've never used a 3.x Volt device before. I see the LPC2148 has "5V
> Tolerant" IO pins.
>
> Can I use them as I would the pins on a 5V device or are there
> things I must be aware of ?
You can connect digital outputs of a 5V device directly to the
LPC2148. Even if its supply voltage is only 3.3V it tolerates up to
5.5V on its inputs.
You can connect digital outputs of the LPC2148 directly to inputs of
a 5V device if the 5V device accepts 3.3V as a valid logic '1'. The
LPC2148 never actively outputs more than 3.3V.
For 5V devices with "TTL" compatible inputs this is no problem. 5V
devices with "CMOS" input levels might require more than 3.3V as
logic '1', so you may have to insert a buffer between the LPC2148 and
the 5V device. Check the Vih values in the 5V device datasheet.
Sometimes you can have an external pullup resistor to +5V, and output a '0'
for logic '0', and set the pin to high-impedance for logic '1' (and let the
resistor pull all the way to +5V).
> As far as the ADC is concerned, the manual says:
> "Measurement range 0 V to VREF (typically 3 V; not to exceed VDDA
> voltage level)."
>
> I need to interface to a device that has a 1 to 5V analog output. Is
> there an easy way to use the LPC2148's 0 to 3V ADC to convert this ?
> A resistor divider comes to mind. Is there a better way ?
A resistor divider is fine if you can use low resistor values so that
the LPC2148 ADC input is fed with a relatively low impedance. If
your external device cannot drive a low impedance you may have to
insert an opamp as a x1 buffer between the resistor divider and the
ADC input.
Karl Olsen
From: "armdeveloper"
To:
Sent: Monday, March 12, 2007 10:06 PM
Subject: [lpc2000] 5V tolerant pin tips ? 5V ADC VREF ?
> I've never used a 3.x Volt device before. I see the LPC2148 has "5V
> Tolerant" IO pins.
>
> Can I use them as I would the pins on a 5V device or are there
> things I must be aware of ?
You can connect digital outputs of a 5V device directly to the
LPC2148. Even if its supply voltage is only 3.3V it tolerates up to
5.5V on its inputs.
You can connect digital outputs of the LPC2148 directly to inputs of
a 5V device if the 5V device accepts 3.3V as a valid logic '1'. The
LPC2148 never actively outputs more than 3.3V.
For 5V devices with "TTL" compatible inputs this is no problem. 5V
devices with "CMOS" input levels might require more than 3.3V as
logic '1', so you may have to insert a buffer between the LPC2148 and
the 5V device. Check the Vih values in the 5V device datasheet.
Sometimes you can have an external pullup resistor to +5V, and output a '0'
for logic '0', and set the pin to high-impedance for logic '1' (and let the
resistor pull all the way to +5V).
> As far as the ADC is concerned, the manual says:
> "Measurement range 0 V to VREF (typically 3 V; not to exceed VDDA
> voltage level)."
>
> I need to interface to a device that has a 1 to 5V analog output. Is
> there an easy way to use the LPC2148's 0 to 3V ADC to convert this ?
> A resistor divider comes to mind. Is there a better way ?
A resistor divider is fine if you can use low resistor values so that
the LPC2148 ADC input is fed with a relatively low impedance. If
your external device cannot drive a low impedance you may have to
insert an opamp as a x1 buffer between the resistor divider and the
ADC input.
Karl Olsen
Reply by ●March 12, 20072007-03-12
At 12:00 AM 3/13/2007 +0100, Karl Olsen wrote:
>---- Original Message ----
>From: "armdeveloper"
> > As far as the ADC is concerned, the manual says:
> > "Measurement range 0 V to VREF (typically 3 V; not to exceed VDDA
> > voltage level)."
> >
> > I need to interface to a device that has a 1 to 5V analog output. Is
> > there an easy way to use the LPC2148's 0 to 3V ADC to convert this ?
> > A resistor divider comes to mind. Is there a better way ?
>
>A resistor divider is fine if you can use low resistor values so that
>the LPC2148 ADC input is fed with a relatively low impedance.
Or just make it part of your anti-alias filter, you do use an anti-alias
filter don't you? Any reasonable sized cap will provide enough charge
storage to not be affected by the S&H cap and it will provide an impedance
quite a bit lower than required. The source impedance now only needs to be
low enough not to significantly effect the anti-alias filter frequency,
often a less onerous requirement.
Robert
http://www.aeolusdevelopment.com/
From the Divided by a Common Language File (Edited to protect the guilty)
ME - "I'd like to get Price and delivery for connector Part # XXXXX"
Dist./Rep - "$X.XX Lead time 37 days"
ME - "Anything we can do about lead time? 37 days seems a bit high."
Dist./Rep - "that is the lead time given because our stock is live.... we
currently have stock."
>---- Original Message ----
>From: "armdeveloper"
> > As far as the ADC is concerned, the manual says:
> > "Measurement range 0 V to VREF (typically 3 V; not to exceed VDDA
> > voltage level)."
> >
> > I need to interface to a device that has a 1 to 5V analog output. Is
> > there an easy way to use the LPC2148's 0 to 3V ADC to convert this ?
> > A resistor divider comes to mind. Is there a better way ?
>
>A resistor divider is fine if you can use low resistor values so that
>the LPC2148 ADC input is fed with a relatively low impedance.
Or just make it part of your anti-alias filter, you do use an anti-alias
filter don't you? Any reasonable sized cap will provide enough charge
storage to not be affected by the S&H cap and it will provide an impedance
quite a bit lower than required. The source impedance now only needs to be
low enough not to significantly effect the anti-alias filter frequency,
often a less onerous requirement.
Robert
http://www.aeolusdevelopment.com/
From the Divided by a Common Language File (Edited to protect the guilty)
ME - "I'd like to get Price and delivery for connector Part # XXXXX"
Dist./Rep - "$X.XX Lead time 37 days"
ME - "Anything we can do about lead time? 37 days seems a bit high."
Dist./Rep - "that is the lead time given because our stock is live.... we
currently have stock."
Reply by ●March 13, 20072007-03-13
hi,
I never try this before and I recommand not to connect to the 1~5V
input to the ADC port.
Instead maybe you can try using proportional series resisters. e.g.
input series resister R1=5.1K then series resister R2K to GND.
the LPC2148 ADC pin samples value between R1 and R2.
--- In l..., armdeveloper
wrote:
>
> I've never used a 3.x Volt device before. I see the LPC2148
has "5V
> Tolerant" IO pins.
>
> Can I use them as I would the pins on a 5V device or are there
things I
> must be aware of ?
>
> As far as the ADC is concerned, the manual says:
> "Measurement range 0 V to VREF (typically 3 V; not to exceed
VDDA
> voltage level)."
>
> I need to interface to a device that has a 1 to 5V analog output.
Is
> there an easy way to use the LPC2148's 0 to 3V ADC to convert
this ? A
> resistor divider comes to mind. Is there a better way ?
>
> Thanks.
>
I never try this before and I recommand not to connect to the 1~5V
input to the ADC port.
Instead maybe you can try using proportional series resisters. e.g.
input series resister R1=5.1K then series resister R2K to GND.
the LPC2148 ADC pin samples value between R1 and R2.
--- In l..., armdeveloper
wrote:
>
> I've never used a 3.x Volt device before. I see the LPC2148
has "5V
> Tolerant" IO pins.
>
> Can I use them as I would the pins on a 5V device or are there
things I
> must be aware of ?
>
> As far as the ADC is concerned, the manual says:
> "Measurement range 0 V to VREF (typically 3 V; not to exceed
VDDA
> voltage level)."
>
> I need to interface to a device that has a 1 to 5V analog output.
Is
> there an easy way to use the LPC2148's 0 to 3V ADC to convert
this ? A
> resistor divider comes to mind. Is there a better way ?
>
> Thanks.
>
