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LMG1025-Q1: driving 50 Ohm Load with 600ns Pulse and 500kHz

Part Number: LMG1025-Q1
Other Parts Discussed in Thread: LMG1205

Hello,

i want to use the LMG1025-Q1 to drive a 50 Ohm Load with a square-pulse with 600ns pulsewidth and 500kHz frequency.

Which load is could be driven?

VDD = 5V

Output = 5V Pulse

Output-Current = 100mA Pulse

I have a TestPCB and there, i see that the output-voltage-value goes down from 5,25V to 4,80V with 600ns-Pulse and 50 Ohm load.

In the Datasheet, i haven't found infos about this behaviour.

With lower frequency (30kHz), the voltage remains at 5,25V with 600ns-Pulse and 50 Ohm load.

-> could it be a thermal behaviour?

Best Regards,

Gerald

  • Hello Gerald,

    Thanks for reaching out.

    Our drivers are typically geared to drive capacitive loads in which case the the output stage FETs are pulsing current to charge/discharge the capacitive load (i.e MOSFET's gate). 

    Assuming the 100mA is the average current through the load (during the 600ns pulse), you're likely stressing the internal OUTH pullup transistor which typically may not see more than 20mA. Can you confirm the IDD current during this period?

    Additionally, from your waveform, there might also be leakage likely due to the resistive nature of the load which might induce junction temperature rise across the IC.

    Does the voltage start sagging at 500kHz or at lower frequency?

    Regards,

    -Mamadou 

  • Hello Mamadou,

    thank you very much for the fast response!

    Oh, ok so i shouldn't select this device for more then 20mA DC current. I don't have measured the current during this period, but i assume this current because of resistive load of 50 Ohm.

    Voltage starts sagging maybe at 200-300 kHz, i haven't been able to measure it at this frequency.

    But at 150kHz, the sagging is not regonizeable. Maybe a little bit ( mVolts ).

    Alternative:

    Do you have a good alternative for this application?

    I need a positive pulse with 200ns to 600ns pulsewidth with very fast RiseTime like this. But also a DC-Current-Capability up to 100mA and the voltage for the output-pulse should be +5V.

    Best Regards!

    Gerald

  • Hi, Gerald,

    I would recommend adding a GaN FET to provide the current as is done in the EVM. As Mamadou mentioned, the LMG1205 is designed to drive the capacitive load of a GaN FET, and not a resistive load.