7.2.2 Detailed Design Procedure

Implementing the SDQ host via bit-banging over GPIO is possible. In this case, consider additional error

checking for the reset routine of the TMF0008 to verify that the responder is operating as expected on the bus.

Whenever the host sends a reset, the responder devices acknowledge the reset with a presence pulse. The host

must confirm, before the presence pulse, that the bus has been released and returned to a high level, indicating

that nothing is holding the bus unexpectedly low. As the minimum tPDH is 15μs, having the host look for a logic

high on the bus 10μs after releasing the bus at the end of the reset is sufficient to confirm the bus is released for

the responder devices to acknowledge.

7.2.3 Application Curves

Te mperature(°C)

-10

0

10

20

30

40

50

60

70

80

1E-6

2E-6

3E-6

4E-6

5E-6

6E-6

7E-6

VPUP = 3.3V

VPUP = 5V

Figure 7-2. Input Load Current (IL) vs Temperature

(Standard Speed)

Te mperature (°C)

-10

0

10

20

30

40

50

60

70

80

1E-6

2E-6

3E-6

4E-6

5E-6

6E-6

7E-6

VPUP = 5V

Figure 7-3. Input Load Current (IL) vs Temperature

(Overdrive Speed)

7.3 Power Supply Recommendations

The TMF0008 is a low-power device that only needs to be turned on when communicating. The device power

comes from the voltage supply that is used for digital I/O in the system. A dedicated VCC pin does not exist in

the device. The device obtains power from the SDQ communication input which can be sustained during normal

communication activity. Do not install any capacitors on the SDQ line.

The ramp time of the SDQ voltage when power is initially applied can be slow due to current limiting from the

source. Ramp times greater than 200µs can cause undesired bouncing of the POR circuit and result in the

device not generating a presence pulse. To account for this undesired effect on the device, a best practice for

the communication host is to issue a “hard” reset to the device by pulling down the SDQ line for >5ms and then

releasing the SDQ bus before issuing the reset pulse that is approximately 480µs long.

Figure 7-4 illustrates the best practice for dealing with initial power-on ramps.

3

4

5

1

2

1.

Initial power-on ramps can be long in duration.

2.

The host issues a “hard” reset of > 5ms, which resets the device

3.

TMF0008 responds to the hard reset by issuing a presence pulse.

4.

A "soft" reset of approximately 480µs can be applied after the previous presence pulse.

5.

TMF0008 responds to the soft reset by issuing a presence pulse.

Figure 7-4. Power-Up Best Practice

www.ti.com

TMF0008

SLVSIV3 – JULY 2025

Copyright © 2025 Texas Instruments Incorporated

Submit Document Feedback

27

Product Folder Links: TMF0008