DS90UB928Q-Q1: PDB and LOCK time

Dongbao Zhou

Part Number: DS90UB928Q-Q1

Hi team,

From the datasheet, we can see lock timeTddlt=6-40ms, Vih(min)=2.0V, Voh(min)=2.95V.

However, in my customer's board, we got below test result, Lock pin ramp up earlier than PDB voltage. Could you kindly explain this? See schematics below, Lock is connected to MCU I/O pin without pull-up or pull-down resistor.

Dongbao

over 8 years ago

0 Steven(Shenzhen) Shi over 8 years ago

TI__Mastermind 30515 points

Dongbao,

1. The lock spec. means the internal CDR lock time spec., after PDB is disable, the high speed input signal should be active and stable. this is the spec test condition;

2. Regarding the LOCK pin waveform, this is the general digital I/O issue during power-up. if you disconnect the MCU I/O with LOCK pin of UB928, the LOCK pin should have same behavior as shown in d/s. the root cause of the test plot could be power-on sequence and MCU's I/O power-on feature.

best regards,

Steven

0 Dongbao Zhou over 8 years ago in reply to Steven(Shenzhen) Shi

TI__Expert 4170 points

Steven,

One thing to clarify, the test is conducted with MCU I/O pin disconnected, thus the MCU influence could be eliminate.
Is there any other possible reason?
Thanks.

Dongbao

0 Steven(Shenzhen) Shi over 8 years ago in reply to Dongbao Zhou

TI__Mastermind 30515 points

do you have any external pull-up voltage? you should leave LOCK pin floating to test it.

best regards,
Steven

0 Dongbao Zhou over 8 years ago in reply to Steven(Shenzhen) Shi

TI__Expert 4170 points

The lock pin is left floating during the test.

Best regards,

Dongbao

0 Steven(Shenzhen) Shi over 8 years ago in reply to Dongbao Zhou

TI__Mastermind 30515 points

Dongbao,
Please secure the power sequence (VDDIO and VDD core) and the test probe's loading. As mentioned, if power sequence is not correct, due to internal ESD protection circuit, with external loading, you should can see such signal in LOCK pin. also, you can try it in our EVM board for verification.

best regards,
Steven

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DS90UB928Q-Q1: PDB and LOCK time