LMG1025-Q1EVM: Unstable Output

Mark Philip Felipe

Part Number: LMG1025-Q1EVM

Hi Team,

Trying to use 10 kHz trigger signal, which consists of two successive pulses with 250 ns delay, to trigger LMG1025-Q1EVM. The trigger signal is shown in Figure 1. The two successive pulses have the same pulse width of 88 ns. However, the optical output of laser source for these two successive pulses is different, shown in Figure 2. The output pulse energy and the pulse width between these successive pulses are different.

Also tried to reduce the trigger pulse width to 50 ns, but the two optical output are still different. Could you please help to solve this problem?

/resized-image/__size/640x480/__key/communityserver-discussions-components-files/196/6303.figure1.PNG

/resized-image/__size/640x480/__key/communityserver-discussions-components-files/196/6521.figure2.PNG

Thank you.

-Mark

over 3 years ago

0 Leslie Marquez over 3 years ago

TI__Genius 9301 points

Hi Mark,

Thanks for your question. Where is the output signal being measured? At the gate of the FET?

If not, please share the waveforms at the input of the driver (as close as possible to the pin) and at the gate of the FET.

Please also share your schematic and VDD and Vbus voltage used.

Regards,

Leslie

0 Mark Philip Felipe over 3 years ago in reply to Leslie Marquez

TI__Genius 9705 points

Hi Leslie,

The output signal is laser pulses that I measured using a photodiode. The VDD and Vbus voltage is 5.5 V and 6.6 V, respectively. I have tried to increase the VDD voltage to 8V, but the output would not change.

The waveforms at the input of the diver (measured as close as to the pin) and the gate of the FET are shown attached.
The testing system and measuring point are also attached.

Thank you

-Mark

0 Leslie Marquez over 3 years ago in reply to Mark Philip Felipe

TI__Genius 9301 points

Hi Mark,

Could you please include the attachments you mentioned? I'm not able to see them on your last post.

Regards,

Leslie

0 Mark Philip Felipe over 3 years ago in reply to Leslie Marquez

TI__Genius 9705 points

Hi Leslie, please see the attachments.

/cfs-file/__key/communityserver-discussions-components-files/196/sn_5F00_customerservice_5F00_case_5F00_dc49a1b31b8af050602cf715464bcbfc_5F00_attachments-_2800_1_2900_.zip

Thank you.

-Mark

0 Leslie Marquez over 3 years ago in reply to Mark Philip Felipe

TI__Genius 9301 points

Hi Mark,

Thank you for providing the waveforms. I'll review the information and plots provided and will get back to you by Monday.

Regards,

Leslie

0 Leslie Marquez over 3 years ago in reply to Leslie Marquez

TI__Genius 9301 points

Hi Mark,

To drive a laser diode load, we recommend to first test with a resistor load to set up the appropriate pulses required for the laser diode. You'll need to size the resistor load (R5-R8) to represent the laser diode's resistance (for a typical 1Q laser impedance solder 4, 4Q, 0603, 100mW resistors for R5-R8). Once you achieve the required pulses for you application then you can take the resistors off and place the laser diode.

Please review section 4 "EVM Operation out of the box" of the EVM user's manual for detail procedure: https://www.ti.com/lit/pdf/sluuc20

Best regards,

Leslie

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LMG1025-Q1EVM: Unstable Output