3.3v Voltage Regulator

[Xenobius]

Hi all,

I have a small problem finding a 3.3v regulator for my application. Here is a small description:

input voltage: 3.3 - 3.7v from a single cell lithium polymer battery
Input voltage can also go up to 4.2v while charging the battery

Circuit requires 3.0 - 3.6v (to drive an ESP 8266)
Total current required is around 350mA at the very most. Maybe 400mA to be super safe.

My problem is that a voltage regulator will need at least 0.7 volts more than 3.3v to operate.
I tried to investigate the option to use a zener diode of the correct wattage but this too requires 0.6v

What else can I try? Thanks a lot

 

[kellys_eye]

Can't you arrange for the battery to be disconnected from the circuit whilst charging? Simple switched socket arrangement would work.

 

[Xenobius]

I could perhaps drive power to the circuit only when the charger is not connected because this needs to be automatic... however if I could leave it connected it would be better for my application.

 

[kellys_eye]

I've seen data sheets for 3.3V LDO regulators that operate from 2.1V to 6V input....
Here's one that fits the bill:

http://uk.farnell.com/microchip/mcp1825s-3302e-db/ic-ldo-3-3v-500ma-sot-223-3/dp/1578404

 

[dorke]

A solution for you would be the LT1763-3.3 or the adjustable version.
At 400mA load it will have a max of 350mV dropout at T=25C.
Here is the datasheet

 

[Xenobius]

Legendary !! That's exactly what I need! Thank you so much guys! Really helpful!

 

[BobK]

Can't you arrange for the battery to be disconnected from the circuit whilst charging? Simple switched socket arrangement would work.

Nope. It still has 220nV typical and 350mV max dropout. To get 3.3V out all the way down to 3.3V, you are going to need a switching regulator.

Bob

 

[dorke]

Nope. It still has 220nV typical and 350mV max dropout. To get 3.3V out all the way down to 3.3V, you are going to need a switching regulator.

Bob

Bob,
the ESP8266 can work down to 3V,
so a 3.3V LDO is fine for this app.

 

[BobK]

OK, I misread it to think he required 3.3V out.

That regulator should work.

Bob

 

[davenn]

Bob,
the ESP8266 can work down to 3V,
so a 3.3V LDO is fine for this app.

except that once the battery drops a bit in voltage, the headroom will be lost
and the output will drop below 3V

as @BobK , a switching reg is the best way to go

 

[dorke]

except that once the battery drops a bit in voltage, the headroom will be lost
and the output will drop below 3V

as @BobK , a switching reg is the best way to go

An LDO like the LT1673 would be perfectly fine down to input voltage of 3.3V and current load of 350(400)mA to produce 3.0V .
In the worst case scenario(400mA) there would be a slight violation of 25mV,It should work fine!

notice,
With dropping voltage to the ESP8266(In the area from 3.3v down to 3.0),
the ESP826 will draw less current, lowering the actual dropout voltage of the LDO and compensating for the drop in the input voltage(see below).

The OP should measure the max actual current the board draws,the lower this current the better.
From the datasheet(at 25C) we get about :
325mV @400mA
305mV @350mA
290mV @300mA

BTW,
1. The data sheet of the ESP8266 voltage states 2.5-3.6V !
2. A switching reg. would produce a lot more noise,
and may badly effect the receiver part in the board,
that is really asking for trouble!

 

[Xenobius]

Wow ok, so many thing I didn't realize. I am using the ESP8266EX which works 3 to 3.6.
Also if a switching voltage regulator makes noise, and at the same time I can work with an LDO VReg, I think that might be a good solution then.

Other than the ESP8266 I am going to drive 2 or 3 leds and at most they would dim slightly not the end of the world.

I was looking at MCP1825S-3302E/DB
Also for completeness sake, I was looking at MCP73831 charging IC which takes the voltage up to 4.2 during charging.

Thanks for the time guys

 

[Xenobius]

This is interesting, according to this datasheet, it may be able to work @ 1.8v in which case if I use a 2V voltage regulator, I might solve my problem easily. http://d1jy6p8pks3hof.cloudfront.net/datasheets/ESP12Espec.pdf

Am I interpreting the datasheet correctly?