What is VDS(max) of the open drain HDQ pin on DM3730 processor?

Stephen Blake

Other Parts Discussed in Thread: DM3730, BQ27000, OMAP3530

Dear Forum,

The HDQ 1-wire pin (hdq_sio ball J25 on DM3730CBP) is an open drain. However, I cannot find the specification of VDS(max) for the open-drain transistor. I guess that one can pull it up to 3.3V but I'm not entirely sure, because I have the mistral DM3730 EVM which buffers the HDQ pin with a 1.8V to 2.8V level translator. What is VDS(max) of the HDQ pin?

Yours sincerely

Stephen Blake

over 12 years ago

0 Biser Gatchev-XID over 12 years ago

TI__Guru**** 393215 points

Hi Stephen,

I don't think you can pull HDQ_SIO directly to 3.3V, since this I/O cell is on the VDDS domain, which is 1.8V.

0 Stephen Blake over 12 years ago in reply to Biser Gatchev-XID

Prodigy 130 points

Dear Biser,

Section 18.6, page 2867 of the DM37x tech ref manual shows the open-drain pin hdq_sio connected directly to a BQ27000 battery gas gauge (which is exactly what I intend to do) with a pull-up to an unspecified voltage Vdd. The BQ27000 data sheet says that the 1-wire connection to its HDQ pin has 1.5V < VIH and VIL< 0.7V. So, if one is only allowed to use a pull-up to 1.8V, the noise margin for a logic high is only 300mV. The VIH value for the BQ27000 gas gauge implies that the device would be happiest if HDQ was pulled up to about 3.3V and this is why I thought it might be safe to pull up to 3.3V . However, I'll take your advice and only pull up to 1.8V and accept the 300mV noise margin.

Yours sincerely

Stephen Blake

0 Biser Gatchev-XID over 12 years ago in reply to Stephen Blake

TI__Guru**** 393215 points

Hi Stephen,

I've also checked other EVM's. On OMAP3530 EVM HDQ_SIO is pulled to 1.8V with 10kOhm resistor, and the processors are pretty much identical. In fact, now that I look at it again, the EVM motherboard is the same and the pullup is R110.

0 peaves over 12 years ago in reply to Biser Gatchev-XID

TI__Guru 62855 points

I have confirmed the maximum recommended high level voltage for this IO is 1.8 volts.

Regards,
Paul

0 Stephen Blake over 12 years ago in reply to peaves

Prodigy 130 points

Dear Paul,

Thank you very much for this information.

Yours sincerely

Stephen Blake

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What is VDS(max) of the open drain HDQ pin on DM3730 processor?