BS2pe sleep mode power question
daviddrake
Posts: 20
In the "Basic Stamp Syntax and Reference Manual 2.1" (which in my opinion is a very well put together book), there is a comparison chart on page 9 that includes data for the BS2pe. It states that current consumption is 15 ma running and 150 ua in sleep mode. In the Stamp Specifications datasheet of 11/2004 it says these figures are 15 ma and 36 ua, a big difference. (The start up time for the BS2pe is also very fast, lowering power consumption.) Would Parallax engineering be kind enough to confirm the correct values? I am in the middle of a low power application design and this would be most helpful.
An unrelated comment, we have been testing the new Ping ultrasonic sensor with very good results.
Your help is most appreciated,
David Drake
An unrelated comment, we have been testing the new Ping ultrasonic sensor with very good results.
Your help is most appreciated,
David Drake
Comments
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Jon Williams
Applications Engineer, Parallax
Dallas, TX· USA
So both the Spec Sheet of 11/04 and the 2.1 book were not accurate? The actual value for the BS2pe is 350 ua in sleep mode?
Additional question -> Is there an industrial temperature range version of the BS2pe available?
DD
SLEEP for the BS2pe is around 50 microamps, which is close to value in the table on page 429 in the version 2.1 manual. There is variation in this parameter for any Stamp, due to spread in voltage regulator quiescent current and CPU watchdog current.
An individual BS2pe out there might come in as low 35 microamps, or as high as 60 microamps. (but not 150 or 350!)
There is also unit to unit variation in the operating current. That is typically in the range from 15 to 17 milliamps for the BS2pe.
During long SLEEP intervals, the BS2pe wakes up for 0.2 millisecond approximately once every 2 seconds and then goes back to sleep. The overall current during long SLEEP intervals is an average of the 50 microamps for 2 seconds with 15 milliamps for 0.0002 seconds, which comes out to not much more, about 55 microamps average. The 2 second figure is variable, and is based on a temperature depended RC timer in the CPU chip. I know the manual says it wakes up every 2.304 seconds, but take that with an enormous grain of salt. That was pretty close for the PIC-based original BS2, but the SX-based Stamps, including the 'pe, come in at more like 1.9 seconds at room temperature. The BS2pe is unique with its short wakeup feature, 0.2 millisecond as compared to 16 milliseconds for the other Stamps. That gives it an good edge in data logging situations where you can make use of SLEEP, NAP, or POLLWAIT.
I have a page up about the BS2pe at this URL: www.emesystems.com/BS2pe.htm. That has more info on the timing and power issues.
There is also a link on that page to my product, the OWL2pe. It has a BS2pe at its core, and all parts on board are industrial rated.
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Tracy Allen
www.emesystems.com
I have looked at your web site and it is a goldmine of information! I assumed that to get to the very low power consumption figures I had to come in to Vdd with regulated +5 from a low quiescent current regulator such as an LTC3400 and avoid the on board linear regulator. The circuit is powering a proprietary commuications device and the BS2pe. Are these very low current levels with or without the on board regulator? Unfortunately the comm device requires 3.5 to 4.5 volts and the BS2pe runs from 4.5 to 5.5. There doesn't appear to be much safety gap around 4.5 volts. So I am using a diode drop to power the comm device from +5. Any advice would be most appreciated. Your notes have been extraordinarily helpful.
Thanks!
David Drake
www.lxtgroup.com
If they're rated lower than 4.5V, you could try to replace the brownout-reset chip.
As I understand, the 4.5 - 5.5V values was picked to keep it compatible with ordinary 5V TTL chips.
(My BS1 runs quite well when powered just from a small 3V button-cell)
You may find that it draws slightly less power, too, when running at a lower voltage, though it may change the timing on the wakeup-cycle and such...
(In other words, don't blame me if it doesn't work
The BS2pe, like all of the Stamps except the original BS2, use the LT1121 regulator to provide 5 volts Vdd at the output from 5.5 to 15 volts Vin. It is a low quiescent current regulator, about 20 to 30 microamps when there is no load at the output (as, when the Stamp is SLEEPing).
I wasn't familiar with the LTC3400, but it does look like a good bet, with its automatic burst mode, for your 3.3 volt system. It's quiescent current in that mode is also about 20 to 30 microamps. I really like Linear Tech products. They are always well thought out, and solid engineering.
Gadgetman, the original BS2 does have a separate reset chip, however, all of the multibank Stamps use the reset circuit that is built in to the SX CPU chip. The only way to change the reset voltage from its standard 4.3 volts would be to ask Parallax for a special order! The original BS1 does not have a reset chip at all, so it coulld operate on lower voltages without modification.
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Tracy Allen
www.emesystems.com
I wasn't aware that the SX chips had an internal brownout circuit...
(Shame on me as I own a BS2p, too)
I doubt that the guys at Parallax will make one that runs onn a lower voltage.
(Too few sales compard to the increased support and documentation overhead)
Maybe the BS2 can be used?