MCP1711: Ultra-Low Quiescent Current regulator
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Hi,
Does anyone use this regulator ? The datasheet says it consumes only 0.6uA of quiescent current ! This is very impressive and very suitable for battery powered sensors. Using 3.7V li-ion battery with this ldo regulator at Vr=3V will use almost full battery energy with almost no energy loss for voltage conversion and give stable power supply. Is it really that efficient or I misunderstood the datasheet ?
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@rozpruwacz It's a good find. The thing to be mindful of is: " Maximum Output Current: 150 mA". Some of the PA radios will draw more than that during Tx.
All of the ultra low quiescent current LDO's I've found have a max output current of <200ma. If you want more than that, the quiescent current takes a jump.
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Yes, the maximum output current is a limitation. The solution could be to power the radio from separate ldo turned on only for transmission.
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so I went for similar ldo that I was able to get quickly TPS782, it is very similar to MCP1711. And I just made a test board with an atmega328p, nrf24l01 and voltage divider for the battery voltage measurement (1.1Mohm). In sleep mode it draws 7uA
Think it is a pretty good result
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Else on the (very) cheap side of things you have the XC6206, ultra cheap and 1uA Iq, with 200mA maximum current you have a bit more margin. But they are really cheap only on Aliexpress/Ebay so if you needed it quickly, not a good solution.
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@nca78 said in MCP1711: Ultra-Low Quiescent Current regulator:
XC6206
Wow! That XC6206 really is inexpensive. Less than 2 cents each. That's a really great find. Thanks!
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@neverdie said in MCP1711: Ultra-Low Quiescent Current regulator:
@nca78 said in MCP1711: Ultra-Low Quiescent Current regulator:
XC6206
Wow! That XC6206 really is inexpensive. Less than 2 cents each. That's a really great find. Thanks!
I'm surprised you don't know about it, it's used a lot (for example on sensors breakout board), it's a SOT23-3 package with "662K" marking.
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Another interesting one, which I may try, is this: http://ww1.microchip.com/downloads/en/DeviceDoc/20005719A.pdf
Not as cheap, but it has a "nearly zero" off-mode current.
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@neverdie said in MCP1711: Ultra-Low Quiescent Current regulator:
Another interesting one, which I may try, is this: http://ww1.microchip.com/downloads/en/DeviceDoc/20005719A.pdf
Not as cheap, but it has a "nearly zero" off-mode current.For powering radio or sensors only when needed yes, but for anything that could stay on for long periods the "ground pin current" is way too high, starting at 80 uA for low currents.
And for price the MIC5205 which seems similar except a slightly lower guaranteed max output current is widely available at below 10 cents on AliExpress. Original is sold around 30 cents per unit on Arrow so still relatively cheap for a quick and reliable source.
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It seems that using this kind of LDO to power the node that has pir sensor is not an easy solution ... The problem I encountered is the load transient response of this LDO (in the datasheet You can find some waveforms). Basically when the CPU is going out of sleep (e.g. to periodically measure temperature), there are large voltage spikes which cause the PIR to trigger itself. These spikes are quite long, so adding even the 220uF capacitor does not solve the problem. I also tried with a 4.7uH inductor between LDO and the PIR, but no change. Does anyone encountered such problems and know how to prevent them ? As a last resort I could use separate LDOs for the PIR and the rest of the node.
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Usually this is related to the radio starting, very common if PIR you are using is SR501.
You can manage it by software by disabling interrupt on PIR/ignoring pin value while you know you are transmitting something.
If it's really related to CPU wake up only, then you can try to lower frequency of CPU just before going to sleep, so at wake up the power consumption will be much lower and maybe low enough to not trigger the PIR. Then progressively increase the frequency up to normal value.
Last solution is to change PIR from SR501 to AM612 or AM312 which are more stable.
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@nca78 said in MCP1711: Ultra-Low Quiescent Current regulator:
You can manage it by software by disabling interrupt on PIR/ignoring pin value while you know you are transmitting something.
But the I would miss the motion detection if it really happened :).
Usually this is related to the radio starting, very common if PIR you are using is SR501.
Yes, I'm using sr501, but it happens also when nothing is sent to the gateway, so I guess that in such case the radio is not woke up ?Thanks for the suggestions, I'll try with the CPU freq, and if will not solve the problem I'll try other pirs.
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@rozpruwacz said in MCP1711: Ultra-Low Quiescent Current regulator:
But the I would miss the motion detection if it really happened :).
The pin should stay high for long enough for you to send data no ?I forgot about a third solution: use another voltage regulator for the PIR Vcc.
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@nca78 said in MCP1711: Ultra-Low Quiescent Current regulator:
The pin should stay high for long enough for you to send data no ?
Hmm, but I don't know if the pin is high because of the voltage spike or real motion, If I choose to ignore the pir state after sleep function timeout (the case when the cpu wakes to check the temperature) I may miss the real motion if it happens in that moment.
I think that the separate LDO would be the best/easiest solution. PIR itself is consuming around 50uA, so additional couple of uA shouldn't be a problem.
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it is on your PIR sensor VCC pin, as close as possible, that you should add your capa, and play with RC time constant to create a stronger buffer. this could be another solution to improve reliability.
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@scalz I tried with 220uF capacitor and 4.7uH inductor. Didn't helped. I even put a shottky diode between LDO output and PIR VCC, and to that I added 220uF capacitor (basic rectifier circuit) and event that didn't help.
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So I checked that the separate LDO is for sure good a solution. So basically I powered the unmodified hc-sr501 module directly from the battery
LOL.
But to make maximum use if li-ion battery capacity I will remove the diode and replace the stock LDO with 3V version of XC6206. Or MCP1700. They both have SOT-89 package and around 1uA quiescent current.
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@nca78
I may end up with two LDO's on a board: XC6206 LDO to provide power while sleeping, to guarantee adequate voltage for a PIR, and a XC6210 LDO, which can deliver 700ma when enabled but which consumes a max of 100na when not enabled. Then I could, in theory, do an OTA firmware upload using LoRa and not run out of juice.
