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AM26C32: What is the Voh value when Ioh is <1mA

Gary Zeng
Intellectual 1115 points
Part Number: AM26C32
Other Parts Discussed in Thread: AM26LV32, AM26C31, AM26LV32E

Tool/software:

Hi Ti experts,

My customer is using AM26C32/TPT4032 for connecting with DSP.

Voh of AM26C32 is 3.8V, which is 4.8V in TPT4032. For competible design, they use two resistors to divide the Voh.

Customer wants to know what the Voh value if the Ioh is <1mA. In datasheet you can see, it is 3.8Vmin when Ioh is 6mA.

  • 0
    Guru 316690 points

    This device has rail-to-rail outputs; for small output currents, the actual VOH will be near 5 V.

    To interface with a 3.3 V device, you should a level shifter, or use the AM26LV32(E).

  • 0
    TI__Guru 72691 points

    As Clemens pointed out, the VoH will swing rail to rail (like the competitor device). VoH max limit assumes a current load which lowers VoH. In a real customer application, the load is just capacitive which should go to Vcc when measured from a DC stand point. 

    Using a resistor divider can lower the switching frequency since this forms an RC constant (true for both our device and competitor device).

    -Bobby

  • 0 in reply to BOBBY
    TI__Intellectual 1115 points

    Hi Bobby and Ladisch,

    Thanks for your reply.

    Customer want to conbine TPT4031/TPT4032 with AM26C31/AM26C32 in same BOM.

    Customer cares about the connection between AM26C32 and MCU. Due to MCU is 3.3V. So they use divided resistors let 5V down to 3.3V for MCU.

    But customer find that when they use our AM26C32. The common voltage is lower than TPT4032. Voh(min) are all 3.8V for AM26C32 and TPT4032.

    Do you have any suggestions for the resistor's value to make AM26C32 and TPT4032 compatible for MCU.

  • 0 in reply to Gary Zeng
    Guru 316690 points

    The actual drive strength of the AM26C32's outputs is not very well specified, and there were changes in the typical value after a PCN.

    The maximum output impedance of both the TPT4032 and AM26C32 is (5 V − 3.8 V) / 6 mA = 200 Ω. The resistor divider should use values much larger than this; 2 kΩ + 3.3 kΩ is OK. (But with 1.8 kΩ + 3.6 kΩ, the output is nearer to 3.3 V.)

  • 0 in reply to Gary Zeng
    TI__Guru 72691 points

    Can the customer just use AM26LV32E? this device supports 3.3V so they wouldn't need to use a resistor divider.

    -Bobby

  • 0 in reply to BOBBY
    TI__Intellectual 1115 points

    Hi BOBBY,

    AM26C32E is 3.3V power supply and w/ internal ESD protection. But its price is 3times of C32. Customer may consider to use it in new product that need small size. Thx.

  • 0 in reply to Clemens Ladisch
    TI__Intellectual 1115 points

    Hi Ladisch,

    Customer want to confirm their design one more time. Is it ok that They use C32 to output 1mA current(5V/5kohm) and use 1.8k and 3.6k resistors in this design to use TPT4032 and AM26C32 at the same time.