Reducing output noise of TPS61222

Maxim Galkin

Other Parts Discussed in Thread: TPS61221, TPS61222

Hello.

I want to use TPS61222 and TPS61221 with two 1V batteries. I need two power supply chain: 5V for analog front end supply and 3,3V for digital supply. Analog front end is very sensitive to power supply noise (band 0...20 MHz). Analog front end consumption are 2 mA (average value), but on time about 250 usec power consumption increase to 200 mA. I want to reduce output noise from TPS61222 IC on pulse time. I added snubber (100pF and 10Ohm in series), but efficiency of TPS61222 was reduced on 10-15%. I want to add LC filter (10uH + 1 Ohm with 10uF) on output of TPS61222. For reduce output voltage pulsations on 250 usec pulse time I added electrolitic capacitor with capacity about 470 uF with low ESR. I need an advice. How can I reduce output noise on pulse time? May I use snubber with TPS61222 and how to calculate snubbers capacitor and resistor values? Whats better on output of TPS61222: LC filter or double RC filter (2-order)?

With best regards, Maxim Galkin.

over 11 years ago

0 Jim Chen (SEM) over 11 years ago

TI__Intellectual 2370 points

Generally ,you can increas the output cap to get a smalller output ripple.

Can you post your schematic?

0 Maxim Galkin over 11 years ago in reply to Jim Chen (SEM)

Intellectual 460 points

Jim-Chen, hello.

Schematic of my DC-DC listed below:

With best regards, Maxim Galkin.

0 Ryan May over 11 years ago in reply to Maxim Galkin

TI__Genius 13700 points

Hello Maxim,

Here are some strong resources for designing snubbers.

Component calculation guide with power dissipation:

http://www.ti.com/ww/en/analog/power_management/snubber_circuit_design.html

A guide to reduce ringing in boost converters:

http://www.ti.com/lit/an/slva255/slva255.pdf

A technical paper discussing a wide variety of snubber topologies:

http://www.ti.com/analog/docs/litabsmultiplefilelist.tsp?literatureNumber=slup100&docCategoryId=1&familyId=751

0 Jim Chen (SEM) over 11 years ago

TI__Intellectual 2370 points

Snubber is useful for reduce SW noise during switching but it has less effect on Vout ripple.

add LC filter (10uH + 1 Ohm with 10uF) on output of TPS61222 may cause stability issue.

If you go to datasheet Figure16 on page 9, you can see that the Vout drop during load transient is around 50mV.How about your test result?

I suggest you do the schematic as datasheet says on page 1.Just connect FB to Vout directly for TPS61222.Then you can test the output ripple during the load transient.If it matches with Figure16,then the DC/DC is working well.

0 Maxim Galkin over 11 years ago in reply to Jim Chen (SEM)

Intellectual 460 points

Hello, Jim-Chen.

I added LC filter (22 uH + 1 Ohm + 10 uF). I will measure noise later and say about results.

I read application note about snubber calculation. I need active snubber for increase efficiency and decrease noise of DC-DC, but i have not sufficient space on PCB for additional inductor placing.

With best regards, Maxim Galkin.

0 Jim Chen (SEM) over 11 years ago in reply to Maxim Galkin

TI__Intellectual 2370 points

I am afraid you could have stability issue with your filter (22 uH + 1 Ohm + 10 uF).

May I know your requirements of the output voltage ripple?

0 Maxim Galkin over 11 years ago in reply to Maxim Galkin

Intellectual 460 points

I need decrease noise on +5V supply chain to 8-10 mVp-p.

0 Jim Chen (SEM) over 11 years ago in reply to Maxim Galkin

TI__Intellectual 2370 points

This seems not very easy to me.

Generally, the ripple during IC operation in steady state is around 10mV.This could be much larger when load transient happens.

0 Maxim Galkin over 11 years ago in reply to Maxim Galkin

Intellectual 460 points

Consumption of my scheme is about 1 mA and 25mA in short pulse (pulse time about 50 usec with current consumption about 25 mA, pulse repetition frequency is 40 Hz). I want to reduce noise in pulse time, because ADC measure input voltage in that time.

0 Jim Chen (SEM) over 11 years ago in reply to Maxim Galkin

TI__Intellectual 2370 points

waht's you Vout noise during the transient?

Can you post a waveform?Zoom in time scale to 2us/div.

8~10mV is not so easy to me.Maybe you can boost the Vout to higher voltage(eg.7V),then use a LDO.

0 Maxim Galkin over 11 years ago in reply to Jim Chen (SEM)

Intellectual 460 points

Ok, I will try to post waveform.

I can not to use LDO, because I need high efficiency.

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Reducing output noise of TPS61222