UCC27211: UCC27211 different package, different input impedance

Hello Rock,

Thank you for supporting the UCC27211. In reviewing the datasheet for the UCC27211 (UCC27210) I see the input resistance is specified as 102 K Ohms for the UCC27210 and 68 K Ohms for the UCC27211.

There should not be a difference in this parameter based on the DDA package or the D package. The input impedance specification is a typical value. There should not be a high impedance such as the 70 M Ohms however. For the DDA package make sure the measurement is from the inputs to the VSS pin, and not to the power pad.

Can you confirm the UCC27711 part numbers are on both packages, and that the 70 M Ohms measurement was not 70 K Ohms? Also confirm that the measurement is to the IC pins and not the power pad.

Confirm if this addresses your question, or you can post additional questions on this thread.

Regards,

Hello Meng,

Thank you for the additional information on the pin measurements.

I have some questions, and suggestions regarding the resistance test method.

Are you using the UCC27211, or the UCC27211A?

For the HI and LI pin resistance, the test condition will be a positive LI and HI voltage with respect to VSS. Although the input pins can withstand high negative voltage as specified, the resistance may be different due to internal clamping circuits. Can you confirm your measurements are with positive voltage on HI/LI?

The common test condition for the input resistance is 3V, which I will confirm. Can you see if +3V on HI/LI results in expected resistance? This resistance may be nonlinear depending on voltage.

I have a UCC27211D which I can start to examine, but not the DDA package available at this time.

Confirm if this addresses your questions, or you can post additional questions on this thread.

Regards,

Hello Meng,

I confirmed the driver input circuits of the UCC27211 which can explain the high resistance readings at low voltage, which is likely the condition of a DVM.

I also confirmed with a DVM the input pins can show high resistance. In the lab, I was only able to confirm the D package which is what I have available immediately.

Since the UCC27211 inputs are designed to handle high negative voltage there is a reverse bias protection. The input has a series diode and a ~95K Ohm resistance to VSS. This is followed by a votlage limiting switch which is turned on when VDD is > than UVLO which has a 180K Ohm to VSS after the switch.

So with VDD at 0V we would expect a typical 95 to 100K resistance when the input is higher than a diode drop. My tests show from 1V to 5V the equivalent resistance is fairly stable. When VDD is on, the expected resistance is typical 63k to 68k due to the parallel combination of the resistors.

To confirm the conditions of the datasheet. Confirm the LI and HI effective resistance by setting LI and HI in the 1V to 3V range which is the expected parameter test condition, measuring the current and determine resistance. With VDD > UVLO. VDD=12V is a typical test condition.

I will look to acquire DDA parts but keep in mind, the different parts will be different lots which will have some tolerance variation. 

Confirm if this addresses your question or you can post additional questions on this thread.

Regards, 

Hello Meng,

I have the DDA parts coming and will test with same method as the D package.

I should have been more clear on the statement you mentioned. When I refer to different parts, I mean the  D package devices and the DDA package devices will be from different IC build lots, and there is some tolerance on the resistances in the IC. So there is some expected variation on  the resistance values.

Can you confirm if you see much difference with VDD applied, and determine resistance of LI and HI by applying 1V to 3V and measure current?

Regards,

Hello Meng,

Pin 7 of the DDA package is the ground reference for the IC. The power pad is referenced to ground via the substrate, but the pin 7 VSS should be used and connected on the PWB traces as the ground reference. Make sure the input resistance measurements are measured with respect to pin 7 on either the D or DDA package.

Regards,

Hello Meng,

The inside of the chip ground is connected to the VSS pin 7. The power pad is referenced to ground, but may have resistance to the chip ground. So for determining resistance of the IC pins, use Pin 7 (VSS) as the ground reference.

Confirm if this answers your questions, or you can post additional questions on this thread.

Regards,

Hello Meng,

Below is a clip from the datasheet pin description table.

As the datasheet states, the power pad is not wire bond connected to the ground pin of the driver, but the power pad is connected to the substrate of the IC. There can be some resistance in this connection since it is a die attach compound. For parameter measurements, and PWB trace connections the pin 7 VSS should be the ground connection reference. To improve thermal performance the power pad should be connected to a ground referenced PWB trace or plane. But this connection should not be considered the current carrying path.

Confirm if this answers your questions or you can post additional questions on the thread. 

Regards,

Hello Meng,

The UCC27211 was released in DDA package in approximately 2011 so there is some limited time span of the age of the parts in the one sample you refer.

It would take quite some research to see if the chip or assembly has changed over time, but there have likely been new FAB and assembly sites added.

Most IC's with the power pad do not have the wire bonded connection from the power pad to the ground pin, and there is some resistance from ground to the power pad. We typically recommend the connection of the power pad to the ground pin which is a very short trace to connect.

Is there a reason this connection is a concern in your application?

Confirm if this addresses your question, or you can post additional questions on this thread.

Regards,