INA851: Input protection

Francesco Palladino

Part Number: INA851
Other Parts Discussed in Thread: TPS55285, LM2611

Tool/software:

The inputs of the INA851 device are individually protected for voltages up to ±40 V over the supply limits. Using the zener diode as the scheme. 








I have a question, if I have a multistage with 16 channels, INA851 (same double supply) for each channel, can I protect all the inputs only with a pair of zener?

over 1 year ago

0 Gerasimos Madalvanos over 1 year ago

TI__Mastermind 33763 points

Hey Francesco,

The Zener diode is present on V+ to ensure that the supply can sink current. This is useful if your supply is generated by an LDO, or a device that cannot sink current safely. This is not necessarily needed if your supply can sink and source current.

One Zener per 16 devices may work, depending on if the overvoltage conditions will not cause the supply voltage close to the device to exceed the absolute maximum rating of the device.

The appropriate selection of Zener diode would ensure that all 16 can be sinking collectively, which would mean you would need the current capability of the Zener to be >16*15mA or 240mA.

Best,
Gerasimos

0 Francesco Palladino over 1 year ago in reply to Gerasimos Madalvanos

Prodigy 20 points

Hi, if I use an LDO like the TPS7A39, with 150mA I can sink on 8 devices?

+1 Gerasimos Madalvanos over 1 year ago in reply to Francesco Palladino

TI__Mastermind 33763 points

Hey Francesco,

Your LDO will only be able to source current on the V+ rail and only be able to sink current on the V- rail. This device specifies that it can source and sink current because it can generate a positive and negative voltage rail. The positive rail cannot sink current, and the negative rail cannot source current. If using this device, you will still need the zener diode to sink the V+ rail current, and to source the V- rail current.

Best,
Gerasimos

0 Francesco Palladino over 1 year ago in reply to Gerasimos Madalvanos

Prodigy 20 points

Sure, I have another question, is there a "simple" solution to generate dual power for 16 INA851, before LDO at +-18V obviously higher for example 18.5 (use INA 851 in the maximum excursion). There are many +-24V or +-15V DC/DC converters on the market, but not +-18V, do I have to make a buck converter with LMR36503R5RPER? Thanks.

0 Gerasimos Madalvanos over 1 year ago in reply to Francesco Palladino

TI__Mastermind 33763 points

Hey Francesco,

The power rail generation is not my greatest strength, so I will forward this thread to the switching converters team. Just looking at latest devices, I don't see an all in one device that generates a +/-18V rail, just a +/-15V rail. So my next thought is two separate devices. Looking at the buck/boost portfolio, there is the TPS55285 that can generate your positive rail, and the LM2611 that can generate your negative rail.

Generally though, since the switching regulators are noisy, the supply rail is overshot, then dropped slightly with an LDO so that the analog rail is cleaner. This is why the suggestion for a zener diode on the supply is given in the datasheet in the case of needing V+ to sink current and V- to source current.

Best,
Gerasimos