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TPS61169: Designing with TPS61169DCKR

Part Number: TPS61169
Other Parts Discussed in Thread: LM3410

Hi Team,
We want to design a valve driver (Shape memory) for one of our projects.
The valve is a shape memory valve with a resistance of 2.2 Ohms and a maximum rated power of 0.3W.
The vale requires a constant current driver.
We have eight (8) such valves of which only four (4) will be operational at any given time.
The 8 valves are electrically connected in series.
The nonoperational valve is bypassed using a MOSFET connected parallel to all the valves (like in the case of battery balancing).
My input is from a 3.7V nominal voltage battery (2.8V - 4.2V).
The current through the valves will be 250mA maximum.

1). I believe, TPS61169DCKR is the best choice for our case. Please suggest another chip if this cant be used.
2). The same chip is not available in mouser or Digikey. Is there any potential alternative for the same?.
3). I believe, when the PWM pin is held low, the IC is disabled and the IC is enabled when the PWM pin is held at 3.3V.
4). Is the TPS61169DCKR IC is able to drive 350mA of load current?.
5). The chip does not support load disconnect, Is there any IC available with load disconnect?.
6). Generally almost all DC-DC converters (buck and boost) mention their Switching current only. How is the switching current related to the output current?.

  • hi shibin

        For the requirement, I would like to know output voltage condition. Not so sure the characteristic of valve, if it is resistive load, there is a condition that input voltage is larger than output voltage when current is small. 61169 can only support boost topology.

  • Hi Mason,
    Thank you for your reply.
    The voltage across any valve is 1V.
    So 8 valves in series give 8V.
    Only 4 valves are only active at a time.
    The remaining 4 valves will be bypassed with parallel MOSFETs connected to each valve.
    The valves are driven using consent current drivers.
    So I hope voltage will be adjusted in the boost topology.
    How about LM3410YSD/NOPB.

  • hi shibin

        So according to your description, a sepic converter is needed as most of the time Vo=4V, and Vin may be higher than that.

        LM3410 can be used in this application to satisfy both current rating and step up/down function.

  • Hello Mason,
    Thank you for your reply.
    The resistance of the valve is 2.2 - 3 Ohms.
    so the voltage drop across the valve will be 3*0.25=0.75V.

    The maximum voltage needed at the output of the blower is the sum of the voltage across 4 operational valves and the voltage drop across FETs = (4*.75) + (4*[0.55*0.25]) =3.55V (adding voltage drop across the sense resistor R=VFB/ILED = 190mV/250mA = 0.76 Ohms, voltage drop = 0.76*250mA = 190mV).
    When only one valve is operational the voltage needed at the output of the DC-DC converter is  (1*.75) + (7*[0.55*0.25]) = 1.71V (adding voltage drop across the sense resistor R=VFB/ILED = 190mV/250mA = 0.76 Ohms, voltage drop = 0.76*250mA = 190mV).
    1). Is my above calculation correct?. Please correct me if I am wrong.
    2). In both the above calculations, sometimes the voltage needed at the output is less than the voltage at the input. Are there any issues with this?

    3). Is the IC LM3410  able to deliver 250mA of current?.

  • hi shibin

        1. Your calculation is correct

        2. This means sepic circuit is needed to realize boost or buck function.

        3. Lm3410 can deliver 250mA

  • Hi Mason,
    Thank you for your reply.
    Page number 15of the datasheet of LM3410 says"A SEPIC converter has the ability to regulate an output voltage that is either larger or smaller in magnitude than the input voltage".
    If my calculations are correct, since the battery voltage can vary from 2.8V to 4.2V, there are some conditions where my required output voltage is above or below the input voltage.
    I hope a SEPIC converter could solve this issue

    How to find the values of the inductors in the SEPIC topology?.

  • hi Shibin

        I just find a document that you can take as a reference to design sepic topology.

    AN-1484 Designing A SEPIC Converter (Rev. E) (

  • hi Shibin

        If there no more question, I will close this thread. Thanks!