PWM driving of Inductive Loads with VND5T100LAJ-E

[Chiranjeevi9391]

Hello,

I am evaluating the VND5T100AJ-E for an automotive application where I need to drive a 24V contactor. My design requirement is i need to drive the IC through the PWM signal as input.

I have reviewed the datasheet but do not see explicit PWM frequency ratings. My concerns are:

1. Does the VND5T100AJ-E support continuous PWM switching for an inductive load?

2. If this device is not recommended for PWM, could you suggest a similar specification alternative part with the same specifications  that is specifically designed for PWM input @stmicro 

[EThom.3]

I apologise for butting in, but I'm trying to understand what it is you wish to achieve.

You need to drive a 24 V contactor for an automotive application. "Automotive" traditionally means 12 or 24 V, and I assume that you are working with a 24 V system.

If you just need to turn the contactor on and off, I would first check if the contactor can handle at least 30 V. If it can, then just switch the contactor on and off using a regular transistor, such as a FET. If it can't, then I would go for a brushed DC motor driver, with built-in current limiting. These are designed to drive inductive loads, and use the contactor coil as the switching inductor.

[Chiranjeevi9391]

here i am getting confusion at present in my schematics we are using this part (VND5T100AJ-E) driving with the DC input at output we are driving the contactor as a load. but now  we are moving to this part(VND5T100LAJ-E) because we need to operate with the PWM input, load is same.
but when i studied the datasheets of both the parts having similar specifications.here my doubt is, this part (VND5T100AJ-E) also works the PWM signal with the same range (1kHz to 2kHz) of frequency or else differ from this part(VND5T100LAJ-E).
1)If both the parts works with same frequency means what is the difference between both the parts?

and also tell me which is best suitable part for my application.
my requirements is mentioned below
Input:PWM signal from the MCU to the driver IC
Output:driver IC output should need to drive contactor(HX241CAB this is the contactor we are using)

[Peter BENSCH · Accepted solution]

First of all: VND5T100LAJ and VND5T100AJ differ essentially only in the package variants and in the values for current sensing. The switching times are completely identical, so you can expect the same achievable switching frequency.

Could it be that you want to reduce the power consumption of the relay with PWM?
If that is the case, then you should take a look at the datasheet for the HCX241CB, where under General Notes, point 4, it says:

Contactor has two coils. Both are used for pick-up, and then in approximately 75 milliseconds, one coil is electronically removed from the coil drive circuit. The remaining coil supplies low continuous hold power sufficient for the contactor to meet all of its specified performance specifications. This provides the lowest coil power possible without the use of PWM electronics that have been known to cause EMI emissions and/or cross-talk on your system control power.

Regardless of the purpose of PWM control: the maximum PWM frequency of 1...2kHz will result in an audible tone, which can only be avoided with frequencies above the audible range, but then increasingly causes EMI problems.

Regards
/Peter

[Chiranjeevi9391]

Hi Peter,

All my doubts regarding the two parts
(VND5T100LAJ and VND5T100AJ) are now clarified.

We would like to know whether STMicroelectronics has any IC with the following functionality/specification:

1. The driver IC input will receive a PWM signal from the microcontroller.
2. The output should remain ON only while valid PWM switching activity is present.
3. If the PWM signal gets stuck in either HIGH or LOW state (loss of switching activity), the output should automatically turn OFF.

Our application is related to contactor driving, and we are looking for a solution with integrated PWM activity supervision / fail-safe functionality.

Please let us know if ST has any suitable part for this requirement, or if there is any recommended architecture/reference design for implementing this functionality.

Thank you.

[Peter BENSCH]

Your request is a new topic, as the original question concerned the VND5T100 family. In addition, the requirements under point 2 are not entirely clear:

1. should the output remain fully switched on as long as a PWM frequency is present, or
2. should the output switch at the same frequency as the PWM and still switch off in the event of loss of activity?

In both cases, there is no ready-made device from STMicroelectronics, so you would need to devise a circuit that implements this together with a downstream switch like the VND5T100.
Case 1 can be built using a retriggerable monostable, a watchdog, or a microcontroller.

Regards
/Peter