DRV8823 Current Rating

Hi RVG,

DRV8823 has its overcurrent protection set to anything in between 1.5A and 4.5A. What this means is that a current higher than 1.5A could induce the device into Over Current Protection.

For this to happen, the current must be maintained longer than 2.5 us. So if you are seeing less than 2.5 us spikes, those would all be sustained.

Another part that can be used to drive 4 DC motors is the DRV8844. It can drive up to 4 DC motors, although if you require to drive the motor in both directions, you will need two power supplies.

I think the best part to drive 4 brushed DC motors with the current levels you are looking for is DRV8412. It consists of 4 full H Bridges with INx interface. You do need to apply a 10 KHz or faster PWM signal in order to drive the outputs properly.

Hope the info helps. Best regards,

Jose Quinones

Hi Jose,

Thanks for the sharing.
For the DRV8823, based on some test done, 1.8A for 0.2s, neither did it damage the device immediately, nor did the OCP kicks in after 2.5us. May I know if the reliability of DRV8823 be seriously compromised if it is used in this manner. The design shall require 2A for around 1s and is not continous. Needed all in one package device to do this due to lack of PCB space if using 2 per. And yes, I need the motor to be drived in 2 directions.
I tried to do the Power Dissipation calculation at 70 deg or 85, 24V @ 1.5A, however don't find the Rds(on) information on the datasheet. Any advise on this?
Would you have any in detail datasheet?

Regards,

RVG

Hi RVG,

How are you measuring this current? Is it on the power supply side, or on the motor winding side? I don't think the device will be able to supply 2A worth of current per H Bridge, as the OCP is set to 1.5A. It may be that one device appears to be allowing more than 1.5A but in essence, any device in the field may kick in at the minimum value so if you design the application to go as high as 2A, then chances are you will start seeing failures in the field.

The RDSon information is on the page 5 table right under the Motor Drivers section.

Best regards,

Jose Quinones

Hi Jose,

Measurement is done on the motor winding side, the output of the driver. You may find the plot as below.

Anyway, would like to check with you on the OCP level, what does it means when the min is 1.5A, max is 4.5A and typ of 3A when the absolute maximum rating is 1.5A. Moreover, based on the datasheet, the current rating can be tweak via the Vref and Isense. If it is said that the device capable of only 1.5A, meaning this function serves only for designer to limit any current less than 1.5A before it trip?

Just to clarify, the tocp (2.5us) is referring to the turn off time of the device before restart or the duration of OC before the device turn off?

RVG,

The OCP min is the smallest OCP you will ever see, as guaranteed by us. For the most part, the great majority of devices will have the OCP set to 3A but to process variations, it is possible to observe the MIN. In other words, imagine you have 1 million devices, the great majority of them will be at 3A, but some will approach 1.5A and others will approach 4.5A.

As you pointed out, the ITRIP can be made to be anything below 1.5A. You can also make it higher than 1.5A if you want to disable current regulation for DC motors, which is an implementation we see utilized fairly frequently. Do note once this is done, OCP will become the current limiting factor.

The deglitch refers to the amount of time the higher than OCP level current must be present before an OCP is acknowledged. For example, imagine you have a 10A surge which lasts 100 ns. Although this current is well past the OCP level, its duration is less than the deglitch time and hence it will be filtered out. If on the other hand, you have a 3.25A spike which lasts longer than 2.5 us, then the device will enter OCP protection.

Hope this info helps. Best regards,

Jose Quinones

Hi Jose,

Sorry but I still don't quite get the OCP limit of 1.5A - 4.5A. OCP is meant to protect the Motor Driver from damages due to Overcurrent. Isn't it said that if the rating is 1.5A continous, any current rating higher than 1.5A should be considered as Overcurrent? Hence, am I right to say that the Absolute Maximum Rating as depicted in the datasheet as the worst case scenario, while in fact in 1 million devices, I can actually get a great majority of them to be capable of sustaining 3A continous? However, due to the internal limited OCP deglitch time of 2.5us, I will never be able to get the 2A for 1s.

Regards,

RVG

Hi RVG,

If the current is below OCP continuoulsy, then the thermal impedance/power dissipation, and the die temperature will come into play. Say the OCP on a device is at 1.55A. In this case, the device should be able to drive 1.5A continuously without triggering an OCP.

However, continuous current is yet another complex matter. If you can cool the device properly, then you can do 1.5A forever. But once the device starts getting hotter and hotter, you will eventually start getting thermal shutdown events (TSD). A second is definitely not a long time, but regardless, what a long time is will depend on how the board was laid out, the ambient temperature and any other heat sinking mechanism being employed.

Like you said, from any number of devices, the great majority of them will have the OCP at the 3A vicinity. Devices are tested to ensure an OCP will not be triggered at anything below 1.5A and that any current higher than 4.5 will definitely trigger an OCP. Where the actual set point lies on a per device basis is not known. For this reason, with DRV8823 is not feasible to obtain 2A for 1 second, unless you parallel the H Bridges.

Now, if the user wants to screen the OCP set point on a per device basis, then it would be feasible to ensure only devices with the right OCP value are used. This, of course, is just a suggestion I offer for informational purposes, as whether it makes economical sense to carry it on or not, is a completely different matter.

Hope this answers the question. Best regards,

Jose Quinones