66AK2H06: IPU and IPD questions

Hi Koichiro,

There is no software control (register) for the internal pullup and pulldown resistors on the device pads. See the datasheet:

Section 4.3 Terminal Functions:
 "Internal 100-μA pulldown or pullup is provided for this terminal. In most systems, a 1-kΩ resistor can be used to oppose the IPD/IPU. For more detailed information on pulldown/pullup resistors and situations in which external pulldown/pullup resistors are required, see Hardware Design Guide for KeyStone II Devices."

Section 4.4 Pullup/Pulldown Resistors

Section 10.2.1DeviceConfigurationat Device Reset:

  "If a configuration pin mus tbe routed out from the device and it is not driven (Hi-Zstate), the internal pullup/pulldown (IPU/IPD) resistor should not be relied upon.TI recommends the use of an external pullup/pulldown resistor. For more detailed information on pullup/pulldown resistors and situations in which external pullup/pulldown resistors are required, see Section4.4."

Best Regards,
Yordan

Hi Yordan,

So the IPU/IPD are enabled all the time during power-up sequence / under reset / normal operation?
In customer’s system, FPGA is connected to EMIF16 and there are weak pull-up on FPGA side.
On the other side, EMIF16 data bus has weak pull-down.
Customer wants to keep the bus Hi state.

According to datasheet table 5.5, the weak pull-down on 66AK2H06 is -170uA(min) and -50uA(max)
FPGA side pull-up is 34uA(min) and 220uA(max).
In the worst case combination, 66AK2H06 side is -170uA and FPGA side is 34uA.
Under this scenario, adding 1kOhm external pull-up with 136uA (=170uA-34uA) current flow results in;
1.8V – (1kOhm * 136uA) = 1.664V on the net. This is over Voh and the net is kept Hi.
Is my understanding correct?

Thanks and regards,
Koichiro Tashiro

Hi Yordan,

Yordan Kovachev said:

Yes, your understanding is correct.

Thanks and regards,
Koichiro Tashiro

Yordan,

Could you answer my last question?

Thanks and regards,
Koichiro Tashiro