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Topic: Very low quiescent current regulator for ESP32 board (Read 2753 times) previous topic - next topic

srnet

I have a ESP32 board running nicley with a deep sleep current of 8uA.

That is with a LoRa device, 2kbyte FRAM, TC74 temperature sensor and a 0.96" OLED display.

The regulator is a HTC7333 (IQ 4uA typical), which is capable of 250mA and is fine until you use the WiFi. The large startup current pulse of the WiFi (250mA+) causes a brown out, so the ESP32 really deserves a regulator capable of 500mA or more, even when there is a 1000uF capacitor across the ESP32 supply rails.

I have spent a while searching the Farnell\Element Web site, and whilst there are 3.3V regulators out there with a circa 250mV drop out the smallest IQ I have found is 35uA for a XC6210. Intended power supply is 4 x AA Alkalkine batteries. I dont want to use a regulator with a shutdown pin.

So does anyone know of an 3.3V LDO regulator, 500mA+, with a quiescent current of less than 35uA ?

 

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ted

The large startup current pulse of the WiFi (250mA+)

 
Reduce startup current by resistor, what is the normal current after startup ?

ted

even when there is a 1000uF capacitor across the ESP32 supply rails.

Show that capacitor on the drawing with  WiFi connection

srnet

A resistor could reduce the startup current but would also reduce the supply voltage, which in turn would make the brownout problem worse.

A 500mA capable LDO (MCP1825) and large capacitor across the ESP32 supply rails, does cure the problem, but that regulator has an IQ of 120uA.

So I would like to find a similar regulator with a much lower IQ.
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larsgregersen

How about using two regulators? One for the ESP32 and one for the wifi circuit?

You could even use the ESP32 to control the shutdown pin of the regulator that is supplying the wifi?

srnet

Quote
How about using two regulators? One for the ESP32 and one for the wifi circuit?
The ESP32 has the WiFi built in, you cannot power the WiFi seperatly.



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larsgregersen

The ESP32 has the WiFi built in, you cannot power the WiFi separately.
Sorry, I thought that there was a way to inject power in to the wifi directly.

I haven't used this device, but a LP5912 from TI might work (500 mA, QI is 30 uA).

Alternatively, you can use a boost converter?

srnet

Quote
I haven't used this device, but a LP5912 from TI might work (500 mA, QI is 30 uA).
Thats a possibility, I originally did not consider the very small SMT components, but it might be feasible to hand assemble that device and arrange a pad underneath for heat dissipation.

Quote
Alternatively, you can use a boost converter?
To be avoided really and not sure how many switchers have an ultra low Iq. In addition one of the main functions of the board will be as a LoRa transceiver device. LoRa operates at up to 20dB below noise and some switchers can significantly affect the very weak signals.

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Wawa

Did you try more than 1000uF on the power rail, and were they low-ESR tantalum.
Leo..

srnet

Did you try more than 1000uF on the power rail, and were they low-ESR tantalum.
Leo..
No, but I did try a 470uF low ESR electrolytic, that did not cure the problem with the 250mA regulator, although with the the 500mA was OK.

I dont have a 1000uF + tant, and they are non-cheap.
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ted

The resistor you need is 10 -20 ohm, calculate voltage drop.
Without schematic -  it look like you discharging 1000uF capacitor by voltage regulator that why you burned it, increasing value of capacitor make situation worse.

Maybe this will work.

http://www.analog.com/media/en/technical-documentation/data-sheets/1086ffs.pdf

google - voltage regulator low Quiescient Current

PieterP

No, but I did try a 470uF low ESR electrolytic, that did not cure the problem with the 250mA regulator, although with the the 500mA was OK.

I dont have a 1000uF + tant, and they are non-cheap.
You need smaller capacitors in parallel with your electrolytic caps. Even low-ESR electrolytics are too slow to be used without tantalum or ceramic caps.

The resistor you need is 10 -20 ohm, calculate voltage drop.
Without schematic -  it look like you discharging 1000uF capacitor by voltage regulator that why you burned it, increasing value of capacitor make situation worse.
I'm sorry, but that's just bull.
Adding a resistor in series will just make the brownout worse.

Pieter

ted

double bull - limiting the current will protect .....

PieterP

Modern regulators don't get damaged by short current surges. They have short circuit protection and thermal shutdown. The OP didn't say that he blew up the regular. The problem here is the brownout.

srnet

You need smaller capacitors in parallel with your electrolytic caps. Even low-ESR electrolytics are too slow to be used without tantalum or ceramic caps.
They are there already, 100nF and 4u7 ceramics.

This particular brownout issue with the ESP32 is well known and cured by using an appropriate regulator and large capacitor, in addition to the normal precautions.

I have since found that Infeon do a couple of SOIC8 500mA regulators, they have an Iq of 30uA. 
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