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Original question:

LMH13000RQEEVM: LMH13000RQEEVM RSET

LMH13000RQEEVM: LMH13000RQEEVM RSET

阿德 陳
Prodigy 40 points
Part Number: LMH13000RQEEVM
Other Parts Discussed in Thread: LMH13000

Hello,According to the suggestion:"datasheet 19 page “The VSET voltage is applied using a DAC through a 20kΩ series resistor."

As shown below

test circuit :

Correction Problem Description

Test Circuit Setting conditions:

single-ended input;DC bias 2V/AVDD 3.3V

(PD = 0);(MODE = 0);(RBIAS=1);Low-Current Mode

The iout current is also locked and cannot be controlled by VSET,VSET'' voltage is locked 2.1V

Is there a problem with the circuit wiring method or design parameters, or is the development board damaged?

  • 0
    TI__Mastermind 31945 points

    Hello, we have received your case and the investigation will take some time. Thank you for your patience.

  • 0
    TI__Mastermind 31945 points

    Hi，

    What voltage input are you giving at VSET pin from DAC. Please note for full range of current in both the Mode, the max VSET which is acceptable and recommended is 2V only. 

  • 0 回复 Lydia
    Prodigy 40 points

    Hello, if the development board's AVDD is powered by 3.3V and the VSET input voltage is 0V, then the VSET" terminal (as shown in the circuit diagram above) will have a voltage of 2.1V. Is this normal?

  • 0 回复 阿德 陳
    TI__Mastermind 31945 points

    Hi,

    Below is the schematic of EVM's VSET input structure. Please can you check and confirm if your customer has populated R11 resistor? By default is it not connected in EVM. But if it is connected the potentiometer R8 state will decide the VSET" voltage. 

  • 0 回复 Lydia
    Prodigy 40 points

    Hello, I tested the LMH13000RQE development board and confirmed that R11, R24, and D3 were removed.

  • 0 回复 Lydia
    Prodigy 40 points

    Hello,According to the suggestion:"datasheet 19 page “The VSET voltage is applied using a DAC through a 20kΩ series resistor."R20" "0R=>20K"

    Is the circuit design with a 20kΩ series resistor for the DAC only suitable for high-current mode with a V105Q121A-940 laser LED as the load?
    Or is it necessary in all situations?
  • 0 回复 阿德 陳
    TI__Mastermind 31945 points

    Hi，

    The 20kohm is not necessary. Not having the 20kohm resistor will only cause a offset current error of few 10s of uA in the output current.

    The VSET input pin a high impedance input, so the current going into the pin will be <100pA. So if there is a voltage drop of around 2.1V across the R20 resistor, probably the device may have got damaged. Can the customer replace the LMH13000 device on the EVM and check once. Also I will suggest not to remove D3. It acts a protection against high voltage applied to VSET pin. Please note the absolute maximum rating for VSET pin voltage is 2.5V. Any voltage above that can damage the device.

  • 0 回复 Lydia
    Prodigy 40 points 
    Thanks for reply,
    Ask again 
    When AVDD 3.3V R20 is 20K in the circuit diagram, there is no VSET input. At this time, the measured VSET pin voltage is 2.21V.
    When AVDD 3.3V R20 is 0R in the circuit diagram, there is no VSET input. At this time, the measured VSET pin voltage is 0.01V.
    Is this situation normal? probably the device may have got damaged.