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Low power, battery operated design with dual linear regulators

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Srijal97:

--- Quote from: ledtester on September 15, 2019, 05:51:02 pm ---I found this thread:

https://esp32.com/viewtopic.php?t=4908

If you look at the next to last post:

https://esp32.com/viewtopic.php?t=4908#p21327

you'll see that the poster's ESP32 system had a voltage dip from 3.3 to 2.9 volts and everything still worked.

--- End quote ---

Oh, that's good. I think I'll test it out once I get the dev board in a couple of days and see what happens.

NiHaoMike:
Are there really no LDOs with a high current rating and a low quiescent current? I have to admit it has been a long time since I have looked for something like that, but it's not exactly that uncommon to find a use for such a device. If nothing else, it shouldn't be that difficult to make one with a P channel MOSFET and a micropower opamp.

mariush:
Have you looked at switching regulators to power the low current part?
You seem to focus on the low quiescent bit, but you're still wasting a lot of battery with a linear regulator.

Here's for example some examples of switching regulators on Digikey :

ablic S-85S1P series :
snt-8a package : https://www.digikey.com/product-detail/en/ablic-u-s-a-inc/S-85S1PD33-I8T1U/1662-3379-6-ND/9489617
snt-6a package (cheaper, no voltage divider block) : https://www.digikey.com/product-detail/en/ablic-u-s-a-inc/S-85S1AB33-I6T1U/1662-3366-1-ND/9489567

• Ultra low current consumption: 260 nA quiescent current
• Efficiency (when under 100 μA load): 90.5%
• Fast transient response: COT control
• Input voltage: 2.2 V to 5.5 V
• Output voltage: 0.7 V to 2.5 V, in 0.05 V step , 2.6 V to 3.9 V, in 0.1 V step
• Output voltage accuracy: ±1.5% (1.0 V ≤ VOUT ≤ 3.9 V) ±15 mV (0.7 V ≤ VOUT < 1.0 V)
• Switching frequency: 1.0 MHz (at PWM operation

Also has separate voltage divider block built in (you can disable it if you don't need it).. for the snt-8a package version that's around 0.5$ more expensive.

Yeah, it's expensive compared to a linear regulator, but if you extend the devices life by some percentage...

If you want something cheaper, maybe look at Torex XC9265A331MR-G : https://www.digikey.com/product-detail/en/torex-semiconductor-ltd/XC9265A331MR-G/893-1307-6-ND/5964917

Up to 200mA, 0.8..2.1uA current for the 3.3v out version


For the high current regulator, you can simply use something with enable pin to put that regulator to sleep when not needed

Some examples... see maybe Semtech SM189

SC189ZSKTRT (SOT-23-5 version) : https://www.digikey.com/product-detail/en/semtech-corporation/SC189ZSKTRT/SC189ZSKCT-ND/2182343
SC189ZULTRT : https://www.digikey.com/product-detail/en/semtech-corporation/SC189ZULTRT/SC189ZULDKR-ND/2182342


shutdown current typ 1uA , max 10uA, up to 1.5a switching current,  around 92%efficiency - see datasheet, page 5 top right corner

 ADP2120ACPZ-3.3-R7 : https://www.digikey.com/product-detail/en/analog-devices-inc/ADP2120ACPZ-3.3-R7/ADP2120ACPZ-3.3-R7CT-ND/2436551

0.3-2uA shutdown current, up to 1.25A output current etc .. more expensive..

Srijal97:

--- Quote from: mariush on September 15, 2019, 08:03:01 pm ---Have you looked at switching regulators to power the low current part?
You seem to focus on the low quiescent bit, but you're still wasting a lot of battery with a linear regulator.

Here's for example some examples of switching regulators on Digikey :

ablic S-85S1P series :
snt-8a package : https://www.digikey.com/product-detail/en/ablic-u-s-a-inc/S-85S1PD33-I8T1U/1662-3379-6-ND/9489617
snt-6a package (cheaper, no voltage divider block) : https://www.digikey.com/product-detail/en/ablic-u-s-a-inc/S-85S1AB33-I6T1U/1662-3366-1-ND/9489567

• Ultra low current consumption: 260 nA quiescent current
• Efficiency (when under 100 μA load): 90.5%
• Fast transient response: COT control
• Input voltage: 2.2 V to 5.5 V
• Output voltage: 0.7 V to 2.5 V, in 0.05 V step , 2.6 V to 3.9 V, in 0.1 V step
• Output voltage accuracy: ±1.5% (1.0 V ≤ VOUT ≤ 3.9 V) ±15 mV (0.7 V ≤ VOUT < 1.0 V)
• Switching frequency: 1.0 MHz (at PWM operation

Also has separate voltage divider block built in (you can disable it if you don't need it).. for the snt-8a package version that's around 0.5$ more expensive.

Yeah, it's expensive compared to a linear regulator, but if you extend the devices life by some percentage...

If you want something cheaper, maybe look at Torex XC9265A331MR-G : https://www.digikey.com/product-detail/en/torex-semiconductor-ltd/XC9265A331MR-G/893-1307-6-ND/5964917

Up to 200mA, 0.8..2.1uA current for the 3.3v out version


For the high current regulator, you can simply use something with enable pin to put that regulator to sleep when not needed

Some examples... see maybe Semtech SM189

SC189ZSKTRT (SOT-23-5 version) : https://www.digikey.com/product-detail/en/semtech-corporation/SC189ZSKTRT/SC189ZSKCT-ND/2182343
SC189ZULTRT : https://www.digikey.com/product-detail/en/semtech-corporation/SC189ZULTRT/SC189ZULDKR-ND/2182342


shutdown current typ 1uA , max 10uA, up to 1.5a switching current,  around 92%efficiency - see datasheet, page 5 top right corner

 ADP2120ACPZ-3.3-R7 : https://www.digikey.com/product-detail/en/analog-devices-inc/ADP2120ACPZ-3.3-R7/ADP2120ACPZ-3.3-R7CT-ND/2436551

0.3-2uA shutdown current, up to 1.25A output current etc .. more expensive..

--- End quote ---

I think I can go for the extra cost of the SMPS. I'll check them in detail later but they seem to be good.

So for paralleling the regulator and smps output, I should stick with the Schottky diode and some capacitors like mentioned earlier?

mariush:
Yes, you could use diodes.
Once you get the high current regulator working and turn off the low current regulator, you could short out the diode on the high current regulator using a mosfet with low Rds(on) ... so you won't lose a lot of current on that diode.
Or you could use a p channel mosfet to keep the output of that high current regulator disconnected until needed.

Something else you could do would be to use specialized ICs for this task, but this would add more cost compared to a diode.

For example here's an ideal diode : https://www.digikey.com/product-detail/en/texas-instruments/LM66100DCKR/296-53541-1-ND/10273271
Here's another: https://www.digikey.com/product-detail/en/maxim-integrated/MAX40200AUK-T/MAX40200AUK-TCT-ND/7599791

There's also controllers or multiplexers which allow you to switch between 2 or several inputs... but they're expensive.
 

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