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TL972: spec check

GARETH OU
Guru 10035 points
Part Number: TL972
Other Parts Discussed in Thread: LM358, LT1013, TLV2376, TLV2333, LM358BA

Hi

Customers use TL972IDR For non-reverse amplification, the action is normal when using dual power supply V+=5V, V-=-5V (The voltage increases with the increase of my VIN)

But switch to a single power supply V+=5V, when V-=0V, the output is always 5V Is there a problem where it is used?

  • 0
    TI__Guru*** 148966 points

    Hello Gareth,

    The input stage of TL972 is not rail to rail. I suspect your input common mode is 0V. This is fine with supply -5V,+5V. It is not good for supply 0V,5V 

  • 0 in reply to Ron Michallick
    Guru 10035 points

    Hi Ron

    Customers currently test to lower the magnification (magnification: 2 times), the input 1-2V output has a magnification change

    Is it because of this parameter?

    If you can help me find one set of single power supply or two sets of OPs

    I input close to 0V-20mV can be amplified

    I have tried LM358 0-3mV, there is no change

    Are there any other suggested products?

  • 0 in reply to GARETH OU
    TI__Mastermind 19227 points

    Hey Gareth, 

    Please post a schematic of your current setup.

    All the best,
    Carolina

  • 0 in reply to Caro Walter
    Guru 10035 points

    Hi Caro

    The picture below shows the tested schematic Currently (VIN+)-(VIN-) is 5V from 0mV input to 30mV output

  • 0 in reply to GARETH OU
    TI__Guru*** 148966 points

    Gareth,

    If input signal full scale is 30mV then you need amplifier with an input offset error less than 0.3mV (1% of full scale) 

    https://www.ti.com/amplifier-circuit/op-amps/precision/products.html#p3318=10000;1258042&p480=2;2&p2max=0.0015;0.3&sort=p1130;asc

    For low cost , optimized for 5V (and lower), and availability, I suggest TLV2376 (faster) or TLV2333 (lower IQ). Almost all dual op amps have the same pinout  (for most packages). LT1013 is an exception.  

  • 0 in reply to Ron Michallick
    Guru 10035 points

    Hi Ron

    Thank you very much for your suggestions

    Can the input offset voltage be adjusted by correction? Because you recommend these two OPs, they should be one-level higher than the original TL972 I used. The customer changed to a single power supply for COST DOWN But this OP is twice as expensive Can you help me find VCM's (V-)-0.1 or above Just find the input offset voltage about mV first

  • 0 in reply to GARETH OU
    TI__Guru*** 148966 points

    Gareth,

    For offset correction (post amplifier, usually software), it is important that offset won't cause the output to reach maximum (VOL or VOH)

    So I lowered gain to 133 and output minimum is raised to 0.415V.

    A 3mV op amp offset will change the output by +/-3mV * 133 = +/-399mV

    So output could be range between 415mV - 399mV = 16mV to 4.403 + 399mV = 4.802V 

    Summary for circuit #2,  [A, C, V, RF, RG] solution, no [B, RH, VREF]
    Parameter Real Values Units Note
    A 165 Ω Make Standard R choice
    C 264,000 Ω Make Standard R choice
    V 5 Volt  
    RF 264,000 Ω Make Standard R choice
    RG 2,000 Ω Make Standard R choice
      
     
    Summary result Point 1 Point 2 Units
    VIN 0 0.03 Volt
    VOUT 0.415 4.403 Volt
    VCM 0.003 0.033 Volt

    This example could use LM358BA if the output doesn't have to sink current from VOUT load.