LM9044: Short to Battery and short to gnd protection for INV and NON-INV inputs

Sunney,

Please see my answers below:

1. Can you please review below scheme for short to battery and short to gnd protection, suggest if changes are required or if there is any other way to implement the same. Since the datasheet mentions use of series resistance from 100 ohm to 1k for input filtering, same resistors can be used for current limiting for clamping diodes? 

Yes, the same 100ohm to 1kohm resistors may be used for both, input protection and filtering.  But since both inputs are already internally protected against shorts to supply, you do NOT need the diodes shown on your schematic unless the shorts are to voltages beyond the supply rails - see below.

2. On pg 9 of datasheet, for input filtering, it is recommended to use filter for differential mode as well as for common mode but in application circuit, there are only two caps are used one across inv and non-inv lines and other from inv to gnd. Do I need to add one more as shown below or two caps will serve for both common mode and differential mode.

In addition to the differential input filtering cap, C1, you do need both input common-mode input filters using C2 and C3.

Hi Marek,

Thank you for your response.

For point 1, yes the inputs are protected against short to supply. However for the following scenarios what is recommended:

Marek Lis said:

you do NOT need the diodes shown on your schematic unless the shorts are to voltages beyond the supply rails - see below.

a. If we consider the battery voltage  (or short to voltage) up to 28V and supply is still i.e. Vcc = 14V. Do we need to add protection diodes in that case?

b. What is the current capability (or injection current) of internal protection so that the series resistor selection can be done within 100 to 1k.

Regards,

Sunney

The Absolute Maximum rated input voltage is 16V (see below) so you may NOT short the input to Vbatt of 28V.  Since you do not show whether Vcc includes 10kohm series resistor or say if Vcc can sink current, you will need an external overvoltage protection.

In such case, in order to protect the input you must add 15V Zener diode together with extrenal ESD diode to clamp the input voltage below 16V.

In this case, the series input resistor value needs to be based on the rating of the external DZ and ESD diode you use.

Hi Marek,

Sorry for not showing the complete circuit.

Here it is.

Marek Lis said:

Since you do not show whether Vcc includes 10kohm series resistor

Vcc has 15kohm series resistor.

There is ESD diode ESDCAN24 which I have not shown earlier.

As per your suggestion to use Zener diode, I have marked the schematic above in RED.

And have done some calculations in order to select the zener diode and series resistor.

I have considered battery voltage range 24-28V. 

Since the inputs are 16V protected internally which comes under Absolute maximum rating, I have used 14V zener diode.

Please let me know your comments.

Sunney