Load dump protection in 48V battery system

Hi Prithvi,

Are you looking for an application circuit to simulate a load dump transient or are you asking how to protect a load dump event for 48V systems?

My guess is that you would need a TVS to clamp the voltage transients from a load dump event.

Ben

The TPS37a-Q1 can handle a transient load dump for 12-V systems, not a 48-V battery system.

Ben

Ben, we are looking for protection from load dump in a 48V system. The challenge with TVS are of two fold:

1. They need to be quite high wattage - 5000W or so to handle the large area under the load dump pulse of a 48V system, which can be expensive. Also since we are looking to build a product for different models of EVs, we don't have a consistent motor profile, so we'll have to characterize the load dump pulse in different conditions to figure out which TVS can handle most, if not all conditions.

2. For a 13s Li battery pack, the max pack voltage would be a bit less than 55V. So TVS's Vbr should be more than this. In this case the Vcl is between 80-85V, which means the DC-DC converter input should be able to handle this voltage, which leave few expensive options.

Hi Marcoo, yes we need higher than 65V, more like 200-300V. One possible option I thought could work is modifying LM5069 with a Zener at the input to make sure the voltage doesn't go beyond 80V. This is similar to what this Maxim's article. https://www.maximintegrated.com/en/design/technical-documents/app-notes/7/7084.html Has this approach been tested with any of TI's ICs? Thanks.

Hi Prithvi,

One way to solve this is to add the following to the pins that will see high voltage:. 2 10k ohm resistors in series with a ~45V TVS in the middle of the resistor to gnd to form a "T" shape. The TVS steps in for positive high voltages and protects any input from seeing higher than its rated value. For negative pulses, the TVS diodes will limit the negative voltage seen at the pins to the negative of its forward voltage to protect the device. its similar to the solution from maxim but the 2nd resistor also protects for negative surges.

As I understand it is as follows:

R1 is 10k, connected to 1. Vin supply  2. TVS Cathode and Vin of LM5069

TVS: Cathode: pin 2 of R1 and Vin of LM5069, Anode: GND

R2 I am not clear how it should be connected.

Also how should SENSE pin be handled in LM5069 in this configuration? Thanks.

R2 is only need if you are worried about negative voltages. no need for r2 for positive voltages. R2 would of been between the TVS and the VIN. since this is no longer a TL431 issue, i have attached the proper group to support you with the LM5069

Hi,

LM74800-Q1 is the ideal solution to handle load dump and input reverse polarity events. Please go through the datasheet and let us know if you have any questions.

Best regards,

Rakesh 

Thanks Rakesh. I think this part works for 12/24V systems, not 48V systems as we can't find a TVS diode which has Vcl max as 60V but has Vbr more than 54V.

Sorry, I accidentally pressed resolved. The load dump voltage can go above 100V, but we don't yet know the duration exactly. It might be in few ms.

Hi Prithvi,

LM5069 can support 80V operation and 100V abs max voltages. LM5069 can be configured as per Figure 1 in https://www.ti.com/lit/an/snva683/snva683.pdf to handle input reverse polarity and 48V operation. However, note that the transients should be limited to 100V with appropriate TVS diodes at the input.

Best Regards, Rakesh

Thanks, anything for voltages higher than 100V?