INA290: how to offset output of INA290

Shengnan Li

Part Number: INA290

Hi, I am using INA290 in a boost circuit for peak current mode control, but the bandwidth is very low at low output(small current), I am not able to do stable control at light load. Is there a way to overcome this ? is there a way to offset the output, so that i can get constant bandwidth of 1.1Mhz?

over 2 years ago

0 Javier Contreras4 over 2 years ago

TI__Mastermind 29280 points

Hello Shengnan,

You can do it a few ways but they come with tradeoffs. You can use IB to your advantage and place an offset at the input resistor to on of the input legs to give you a positive voltage at the input. Then you would have to adjust your what your output is for a specific current. This would cause issue with gain error and of course your offset error which you are doing on purpose. So this may need calibration.

Another option is adding a output bias the another circuit as seen here: https://www.ti.com/lit/an/sboa545/sboa545.pdf

The third option is using he INA296 but this is in preview mode and is not yet released.

0 Shengnan Li over 2 years ago in reply to Javier Contreras4

Expert 1010 points

Hi, Javier,

Thanks a lot for your reply. Can i get some INA296 samples for test?

Regards,

Shengnan

0 Javier Contreras4 over 2 years ago in reply to Shengnan Li

TI__Mastermind 29280 points

Hell Shengnan,

Please order devices from our website. https://www.ti.com/product/INA296A or the lower grade version https://www.ti.com/product/INA296B. We only have two gain options available at this time.

0 Shengnan Li over 2 years ago in reply to Javier Contreras4

Expert 1010 points

Thanks a lot. What is the difference between slew rate and bandwidth? 290 and 296 have similar bandwidth but very different slew rate.

0 Javier Contreras4 over 2 years ago in reply to Shengnan Li

TI__Mastermind 29280 points

Hello Shengnan,

The bandwidth is small signal meaning that the output changes normally less than 100mV. This is the response time of the input and output and there is no limitations due to the slew rate. The slew rate is the maximum speed the output can change. Normally once the output is increase in amplitude the bandwidth will be limited by the slew rate. This is due to the fact that the slew rate required increases as you increase the frequency.

Max Slew Rate of sine wave = 2π*Frequency *Amplitude.

0 Shengnan Li over 2 years ago in reply to Javier Contreras4

Expert 1010 points

Hi, Javier, thanks a lot, again.

If I suppose to have an output like in the drawing, from slew rate point of view, INA296(1MHz bandwidth and 5v/us slew rate) should be able to do it. but from bandwidth point of view, a triangle of 1Mhz, needs fundamental and 3rd, 5th, 7th harmonic to be able to get to accurate wave shape. so my question is: is INA296 able to output a 1MHz triangle waveform?

0 kai klaas69 over 2 years ago in reply to Shengnan Li

Guru 140200 points

Hi Shengnan,

even without simulation it should be clear that a 1MHz triangle wave cannot be reproduced by an amplifier showing a bandwidth of only 1.1MHz. All harmonics will be gone then. And this is not a question of slew rate as your signal would have a slew rate of 0.6V / 500ns = 1.2V/µs while the INA290 offers a slew rate of 2V/µs:

li_ina290.TSC

You would need a way faster amplifier for your 1MHz triangle.

Kai

0 kai klaas69 over 2 years ago in reply to kai klaas69

Guru 140200 points

And here the frequency response:

See how much the harmonics are damped. You will no longer see a triangle wave at the output but only a sine wave.

Kai

0 Shengnan Li over 2 years ago in reply to kai klaas69

Expert 1010 points

Hi, Kai,

Thanks a lot. Two more questions:

1. what causes the phase delay?

2. in this case, do you think it is ok to use this amplifier for 1MHz switching?

0 kai klaas69 over 2 years ago in reply to Shengnan Li

Guru 140200 points

Hi Shengnan,

the phase delay is the perfectly normal behaviour of an internally frequency compensated amplifier which every standard OPAmp shows as well:

No, I wouldn't use this amplifier for 1MHz switchings as it does not offer any gain reserve.

Kai

0 Shengnan Li over 2 years ago in reply to kai klaas69

Expert 1010 points

Kai, thanks a lot.

Can you recommend an opamp can do 1Mhz switching?

0 kai klaas69 over 2 years ago in reply to Shengnan Li

Guru 140200 points

Hi Shengnan,

let's wait what Javier is saying to all this.

Kai

0 Javier Contreras4 over 2 years ago in reply to kai klaas69

TI__Mastermind 29280 points

Hello Shengnan,

So the INA290 is the fasters current sense amplifier we have. AS Kai said we do not have everything available for the INA296 but I don't expect the bandwidth be be larger than that of the INA290 operating in the optimal condition. The INA290A1 has the largest bandwidth of the gain options. So the simulations above are a good representation at ideal inputs. The INA296 will not be faster.

You may have to change to a high speed amplifier. You can see an example below. With this you need to account more for the voltages and the gain used for the full bandwidth. The design below uses two stages.

www.ti.com/.../TIDA-00976

Also someone posted a tina simulation of this. /cfs-file/__key/communityserver-discussions-components-files/14/THS4131-High-Side-Schematic_5F00_1.TSC

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/705289/current-and-voltage-sensor-circuit

If you lean toward this you I will have the high speed amplifier team support you.