Can we use a boost converter to produce negtive output?

Jerry Tang

Intellectual 440 points

Other Parts Discussed in Thread: TPS63700, TPS61085, OPA320

There are a lot of boost converters among TI products.Can we use a boost converter to produce negtive output?

For example,the input is 3V,the expected output is -5V. Would you please give me the reference design?

Thanks!

over 9 years ago

0 JohnTucker over 9 years ago

TI__Guru**** 191445 points

That would use an inverting buck-boost topology. Typically you would use a buck converter for that. What output current do you require?

0 Brigitte over 9 years ago

TI__Guru 65470 points

Hello Jerry,

You might have a look at TPS63700. This is an inverting buck-boost converter.

Best regards,

Brigitte

0 Helen chen over 9 years ago

TI__Mastermind 40080 points

What is the -5V output accuracy ?

You can refer to the TI design PMP9770. Get -5V by a negative charge pump.

0 Jerry Tang over 9 years ago in reply to Helen chen

Intellectual 440 points

Hi Helen,
If using the charger pump to get -5V with TPS61085,what about the output voltage accuracy and how to get lower ripple?
Thanks!

0 Helen chen over 9 years ago in reply to Jerry Tang

TI__Mastermind 40080 points

What is the -5V output current? so that I can evaluate the possibility of the charge pump solution.

I think the voltage accuracy can be assured by zener diode if the precision requirement is not so high.

Is there any positive output for this Boost converter?

0 Jerry Tang over 9 years ago in reply to Helen chen

Intellectual 440 points

The desired -5V output current is 100mA.Is it possible?

If using the TI design PM9770,what's the maximum output current by the charger pump?

What factors influent the output voltage accuracy when using charger pump?

How to get lower ripple?

0 Helen chen over 9 years ago in reply to Jerry Tang

TI__Mastermind 40080 points

When the load changes, the output voltage will change a little. So is 100mA a stable load? Or it is a maximum load?

0 Jerry Tang over 9 years ago in reply to Helen chen

Intellectual 440 points

Hi Helen,

100mA is maximum load? Can we get it from the charger pump?

At the same time,we expect to get lower ripple,what methods can we

use it?

0 Shivg over 9 years ago in reply to Jerry Tang

Prodigy 130 points

Vin(Lipo,1000mAh)	3.3V	1A
Vout(-ve)	-5V	10mA
Vout(+ve)	+5V	<250mA

Hi there,

I wanted to use TPS61085 in my power supply circuit, with input/output voltage requirements in table above. Main consideration is the current output.

I will use it to power a opamp circuit(+-2.5V @ 10mA) and wifi module(requiring more than 250mA current at 3.3V).

Op-Amp is OPA320.

0 Shivg over 9 years ago in reply to Shivg

Prodigy 130 points

Please suggest me the circuit, and value of the inductor for current requirements.
Also what is the function of "PNP - zener" combination at the output of charge pump circuit of negative supply. Thanks

0 Helen chen over 9 years ago in reply to Shivg

TI__Mastermind 40080 points

Output + -5V or + - 2.5V? there are different values in the description.

0 Shivg over 9 years ago in reply to Helen chen

Prodigy 130 points

TPS61085,PMP9770

Ohh sorry for confusing question, I need +-5volts output from 3.3v from li-po battery of 1000mAh. Also current required is more than 250mA.

I needed to use TPS61085.

Attaching the circuit schematic(attached below), wanted some feedback.

0 Shivg over 9 years ago in reply to Shivg

Prodigy 130 points

Mistakenly attached the wrong circuit. Attached below is the correct schematic.

0 Helen chen over 9 years ago in reply to Shivg

TI__Mastermind 40080 points

The schematic is OK, only one point:

For the compensation network , if you choose Rcomp=10k, Ccomp=1.5-2.2nF(suggest you use 2.2nF), then the effective output capacitance should be >=10uF, I found you only add 1pcs 10uF cap at the +5V output side, the effective capacitance is not enough, please use at least 2pcs 10uF ceramic cap at the output side. if the package is very small, may need more. you need to check the ceramic cap datasheet to get it.

0 Shivg over 9 years ago in reply to Helen chen

Prodigy 130 points

Thanks you so much Helen, I will make the changes and revert you back with results.

0 Shivg over 9 years ago in reply to Shivg

Prodigy 130 points

Hi,

Getting the required output of +5 volts and -5 volts. But the current output is very less about 50 - 80 mAmps.

I need more than 250mAmps.

Please tell the factors controlling the output current.

I have chosen:-

Rcomp:- 10k, Ccomp:-2.2nF(Ceramic), Cout:-22uF, L:- 3.3uH,

For charge pump circuit Capacitor Values are:- C8=1uF(Electrolytic), C5=4.7uF(Electrolytic).

Once again I repeat the requirements:

Vin(Lipo,1000mAh)	3.3V	1A
Vout(-ve)	-5V
Vout(+ve)	+5V	<250mA

Output current should be more than 250mAmps @+ 5volt output.

0 Helen chen over 9 years ago in reply to Shivg

TI__Mastermind 40080 points

i'm wondering the efficiency is very low which cause the problem. Or your input wire is very thin and long which leads to a big voltage drop on the trace.

could you please share the detailed application information with us? Like in what kind of equipment? Volume? Which company? You can send the information to me by email, my email address is helen-chen@ti.com

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Can we use a boost converter to produce negtive output?