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10K pull-up resistor impact TXS0108E VOL and VOH levels?

Atthen
Prodigy 60 points
Other Parts Discussed in Thread: TXS0108E

Hi,

I'm working on a design to replace an old +5V I/O standard CPLD to +3.3V I/O standard FPGA. 

And, looking for voltage level translator to interface between +3.3V I/O (from FPGA) and +5V I/O (to peripheral IC and microcontroller).

Max datarate requirement for I/O is 60Mbps during communication between +3.3V I/O FPGA and +5V I/O microcontroller.

My concern is some of the I/O have 10K pull-up resistor tight to +5V.

Can I use TXS0108E?

Would 10K pull-up resistor impact TXS0108E VOL and VOH levels? From my understanding, this is only impact TXB type of translator.

If microcontroller I/O is using push-pull driver, can I achieve 60Mbps datarate? Or, the datarate will slowly increase from 2Mbps to 60Mbps?

Please advice.

Thanks..

Best Regards,

Atthen

  • 0
    TI__Expert 4705 points

    Hi, Atthen,

    yes, when you add the external pull up resistor for TXS0108 with 10K, it will raise the VOh and VOL.

    so the main concern is VOL, you can check in the datasheet , the VOL is higher, and not the standard TTL. if you add the 10K, when the out put is Low, it will sink more current into the part, so the VOL will be higher. the max Pull up resistor you can calculate like below.

    Rex-up >=  [Vcc-Vol(max)]/Iol(max), in datasheet,

    VOLB(max)=0.55V when VccA=3.3V, VccB is 4.5V @Iol=650uA Via=0.15V.  so the Rex-up(min)= (4.5-0.55)/650uA =6kohms. so 10kohms should be ok, and can have the max VOL<=0.55V.

    usually, when you choose the TXS part, please check thedriver side can provide the Vil and Vih and receiver side can accpet the VOL and VOH for the TXS parts. this is the main checking.  

    yes, if it is the push-pull driver, it can achieve to 60Mbps at 3.3 VCCA and 5V VCCB.

    any further thing, please let me know. if your application is not for  the bi-directional translation and your VOL has the risk, you can choose the SN74LVCXXX parts, but it needs the DIR control.

    BR
    junjie