VND5T100 - Reverse polarity protection

smiller9 · ‎2016-12-13

Posted on December 14, 2016 at 07:23

Hello,

I have made the reverse battery protection according to the datasheet and the UM1557 (user manual) with a diode in the GND line in parallel to a 4.7kOhm resistor.

But if I do a reverse supply I detected a high current consumption.

This is due to the resistors at the CS outputs that are connected to ground. In my case these are 2.2kOhm resistors. They are only of the size 0603 and they will get destoryed in case of battery reversal.

But there is no advice in the datasheet or the user manual. What can I do to protect these resistors. Is it only possible by increasing the case size?

F G · ‎2017-02-08

Posted on February 08, 2017 at 10:06

Hi, where do you detect the high current? Are you referring to the output current (Iout) or to the CS current? Which load are you using? Value of reverse battery?

Mauro Chiara · ‎2017-05-29

Posted on May 29, 2017 at 11:29

Hi,

I had a similar issue with VND7140AJ.

I have mounted the inversion protection circuit suggested in the datasheet (using a shottkly diode).

When I gave 12Vdc reverse supply voltage I have the ic irremediably damaged.

As a matter of fact, I had 20ohms between the Vcc and the GND pin of the

VND7140AJ.

What could be the cause of such a break down?

Thank you

Best Regards,

Mauro Chiara

Nickname15513_O · ‎2017-06-13

Posted on June 13, 2017 at 10:53

Hi,

could you please provide further info about the components used for the protection circuit?

Have you already had a look at the Application Note UM1922?

Best regards.

Davide

Mauro Chiara · ‎2017-06-15

Posted on June 15, 2017 at 10:00

Hi,

Thank you for your reply.

Please see the attached schematic.

I'm using a schottky SS14. R18 is not mounted because my load is purely resistive.

In the next release I will pull FaultRST and SELn to GND through a 10k resistor. Then I will add a filtering capacitor on the V_power.

At the moment I have solved the problem inserting a diode against inversion also in the positive supply side.

Before that I had many

VND7140AJ damaged.

Best Regards

Mauro Chiara

F G · ‎2017-07-04

Posted on July 04, 2017 at 13:30

Hi Mauro,

I'm sorry but, in the schematic you posted, I cannot see what is the path leading to have only 20Ohm between Vcc and GND.

Resistor between PWR GND and Device GND is 4.7K, Multisense resistor is about 1K and all the prot. Resistors are ~10K.

When you apply the reverse battery, what is your load?

Please, give me further details

Regards

FG

Mauro Chiara · ‎2017-07-05

Posted on July 05, 2017 at 09:13

Good Morning,

I've found what was the reason why VND7140AJ broke down and presented

a 20ohm path between VCC and GND pin of the chip!!

Without the input Rprot (10K) the chip is not protected by inversion just because in this new family of HSD you suggest to take the MCU reference GND before the diode (on the Cathode).

We are used to the old version in which you suggest

to take the MCU reference GND next to the protection diode (on the Anode).

You should underline that Rprot is ESSENTIAL against power supply inversion protection for the protection circuit you suggest!

Best Regards,

Mauro Chiara