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SN74LVC16T245: SN74LVC16T245 power consumption

Nir Flysher
Expert 3367 points
Part Number: SN74LVC16T245

Dear Team,

Can you please help with the below customer question

Please help us with following problem / or forward our question to TI:

 

We are using the SN74LVC16T245 ( in BGA microstar package) - SN74LVC16T245ZQLR

 

In our design we use only 4 inputs out of 16 bits.
The rest , 12 bits , the inputs are connected to GND, and the 12 outputs  related to the unused inputs are left floating. DIR is set accordingly.

We see that when OEn=0 , the current consumption is low ( about 20 uA ), and when OEn=1 the current us rising to more than 10mA.

Is it because the 12 unused outputs are left floating ?

We see  statement on 1st page of attached data sheet:

“The input circuitry on both A and B ports always is active and must have a logic HIGH or LOW level applied to prevent excess current”

 

(our problem is that now we got the PCB already and can’t try / modify it in this stage)

Best regards

Nir

  • 0
    TI__Mastermind 24975 points

    Hello,

    Yes, when the A side is active it will drive the B side into a defined low state to ensure that there is no leakage. When the outputs go into high impedance, the inputs to the B side are floating, so this can cause excess current through the device. This would be expected behavior and the best way to overcome it would be to put both A and B side to ground so that they are always defined and there is no excess current.

    Even for the B side channels that are being used, it is best to have pulldowns or pullups to ensure that they are not floating when the outputs go high impedance, these can be relatively large to ensure current is limited through them when the outputs are driving.

    At this point, unfortunately, I can't think of any other way to solve this problem than to fix the B side inputs. 

    Furthermore, I would like to question if this is the right part selection. 

    If they are only using 4 bits and they are only working in a unidirectional manner, would it be better to have a device that fits this specification, or am I misunderstanding? 

    What are the voltage input and output levels? They could consider using a number of other devices such as the following:

    http://www.ti.com/product/sn74lv4t125

    http://www.ti.com/product/sn74avc4t234

    http://www.ti.com/product/sn74avc4t245

    And if they just need down translation, then they can use a simple buffer to handle this such as the following:

    http://www.ti.com/product/SN74LVC125A 

    Best,
    Michael