TXS0108E: sink current capablity

Given Ding

Genius 10115 points

Part Number: TXS0108E
Other Parts Discussed in Thread: SN74LVC1G07

Hi Team,

below is the application

the luminous diode need 5mA sink current ( 7mA max). and we find B point voltage is ~1.8V @ 5mA, ~3V@7mA.

below are the questions

1. what's the sink current capability of B point?

2. if VOL is too high, will it affect the normal operation of TXS1018?

Thanks.

BRs

Given

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 316690 points

The TXS is a passive switch, so it has no V_OL. All the current must be sunk by the MCU. (Also see [FAQ] Why are the TXS01xx VIH/VIL specifications so stringent?)

If you need more drive strength than the MCU can provide, use a buffer like the SN74LVC1G07 (its open-drain output is overvoltage tolerant).

0 Given Ding over 2 years ago in reply to Clemens Ladisch

TI__Genius 10115 points

Hi Clemens,

Thanks for your reply.

so the current capability is decided by the MCU and MCU is OK for the current, then the voltage on point B doesn't affect the normal operation of TXS1080E, right?

based on the sch above, it seems like a negative feedback system. when current increases, point B voltage becomes higher, then voltage on the luminous diode is smaller, then current decreases, right? Thanks.

BRs

Given

+1 Clemens Ladisch over 2 years ago in reply to Given Ding

Guru 316690 points

Yes, this is how current regulation with a resistor works. (The TXS does not change this behaviour.)

As shown in figure 7-2 of the datasheet, the TXS itself has an on-resistance of about 350 Ω.

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TXS0108E: sink current capablity