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TMP300: Temperature dependent oscillator

Ron Slezak
Prodigy 10 points
Part Number: TMP300
Other Parts Discussed in Thread: NE555,

Using TMP300 to drive the Reset pin on an NE555. NE555 Reset Pin Iih and Iil are specified as max .4ma. TMP300 Iol is 5ma @ .3V. Reset pin of NE555 has 47K ohm to Vcc pull-up. Circuit is non-functional when connected together. Voltage measurements indicate excessive load on TMP300 . Degraded Voh  and Vol voltages on Reset pin. Your comments or suggestions please.

  • 0
    TI__Expert 7855 points
    Ron,

    Do you have a schematic of the circuit?
    What is the Voh and Vol of TMP300 with and without NE555 loading? What is the VCC? The datasheet specifies that the test condition for TMP300 is Isink=5mA, which results in a 0.3V max Vol. That is if VCC=5V, the pull up resistor for the TMP300 output has to be 1kohm to guarantee this 0.3V max Vol. Do you have the same issue if you use a 10khom pull up?

    NE555 reset pin requires as much as 0.4mA to drive it. Assuming your VCC=5V, the max pull up you should use is 5V/0.4mA=12.5kohms. Using the 47khom may be too high to drive the reset pin to proper levels. This issue is compounded when you have another device (tmp300) sinking additional current when it's asserted. Well that's my initial assessment.

    -Kelvin