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DRV110 The hold current is weak

Other Parts Discussed in Thread: DRV110

Hi Team,

The customer is using DRV110 and the attachment is the schematic. And the customer is using the 8pin IC. He refer 

Q: He tests the hold current is 50mA ,and Ipeak is 2A.  On page17 of tidu578.pdf, we can see the formula for Ihold. Ihold=2A*0.35=0.7A. So the customer confuses the test hold current is weaker than the calculated hold current . What is the reason? How to solve the issue?

DRV110_sch.pdf

 

  • Hi Mickey,

    Our experts have been notified and should reply soon.
  • Hi Rick,
    OK. I am waiting for your reply.
  • Hello Mickey,

    The hold current on the 8-pin device is fixed at 50 mA if a 1-ohm R_SENSE resistor is used. TIDU578 uses the 14-pin device, which has a configurable hold current. The formula you reference above calculates a hold current that will be reliable for relay operation over temperature.

    If the customer wants to modify the hold current, they can do it two ways:
    1) Switch to the 14-pin device and set the hold current with a resistor on the HOLD pin (recommended)

    2) If they want to use the 8-pin device, they can control the current somewhat by changing the value of the R_SENSE resistor. I believe they can do this according to this formula: I_HOLD = 50 mA/R_SENSE.

  • Hi James,
    Thanks. The customer said they must use 8pin device because of the PCB restrictions.
    Q1: Is the customer's schematic correct? Is the R_SENSE R3 in the customer's schematic?

    Q2: Is the formula 8 in tidu578.pdf not suitable for the 8pin device?  The formula 8 is Ihold=0.35*Ipeak.

  • Mickey,

    A1) The schematic looks correct. The customer can remove R6 and R7 and leave the EN pin floating. There is an internal pull-up resistor on the EN pin, so the DRV110 will energize the solenoid when it is powered.

    If the customer wants the hold current at 700 mA, they will need to change the following items:

    R3 = 0.07 Ohms

    R1 = 430 kOhms

    A2) Formula 8 in tidu578 does not configure the DRV110 device for a specific current. It is a recommendation for design given by relay manufacturers. Formula 3 on page 8 of the DRV110 datasheet configures the hold current for the 14-pin device. The 8-pin device does not have a configurable hold current because it does not have a HOLD pin. The suggestion I give in my first answer is a workaround for setting the hold current to a different value, but I am not sure how good the performance will be. The recommended solution for setting a hold current is to use the 14-pin device.

    Can you please send me the datasheet or part number of the coil they are using?

  • Also, R3 is the sense resistor in the customer schematic.
  • Mickey,

    I was looking at their schematic again, and they can save space on the board if they put OSC pin to ground. At R_OSC = 200 kOhm, F_PWM = 20 kHz. 20 kHz is also the default setting when the OSC pin is grounded.
  • Hi James,
    Q1: The customer said R3 are the three 0.68 ohm  resistances and they are in parallel, that is R3 is 0.23 ohm. I_HOLD=50mA/0.23=217.4mA. But the customer tests the I_HOLD is 50mA. Is there any other reason?

    Q2: I send the customer a EXCEL to calculate the parameters. Look the attachment. Is the EXCEL suitable for the 8pin device and the 14pin device? Or the EXCEL is only suitable for the 14pin device?

    Q3: For the 8pin device, what is the formula for Rosc ,Rpeak and Cpeak?  What are the  formula differences between the 8pin device and the 14pin device for

    Rosc ,Rpeak,and Cpeak?

    4265.DRV110 Parameter Selector (1).xlsx

  • Mickey,

    A1) I think there might be another reason. The resistance of the coil can limit the current instead of the DRV110 regulating it. For regulation in the hold state, Vsupply/Rcoil > Ihold. The same is true for regulation in the peak state (Vsupply/Rcoil > Ipeak). You can check if the part is regulating by putting a oscilloscope probe on the OUT pin. If the OUT pin shows a PWM signal, then the current is being limited. Also, you can measure the voltage at the SENSE pin. For the 8-pin part, the threshold of the SENSE pin is set at 50 mV by default. If you see less than 50 mV being held there, then the resistance of the coil is limiting the current.

    What is the Vsupply and coil resistance the customer is using?

    A2) The parameter calculator you sent can be used for both devices. However, on the 8-pin device, you ignore the HOLD resistance and current because it cannot be set. I've created a 8712.DRV110 Parameter Selector.xlsxfor the 8-pin part. However, I_HOLD is a calculated output based on the chosen sense resistor.

    A3) The formulas for designing with the 8-pin and the 14-pin are the same, except that the formula for I_HOLD doesn't have any meaning for the 8-pin because there is no HOLD pin. You can find the formulas for I_PEAK and t_KEEP on page 8 of the datasheet and R_OSC on page 9.

  • Hi James,
    Thanks for your reply. I will query the customer about the Vsupply and coil resistance.