SN74LVC3G34: SN74LVC3G34DCUR driving capacity

Kelly Wang

Part Number: SN74LVC3G34

I am using SN74LVC3G34DCUR as a driving buffer to drive 3 leds. The circuit is same as section 9.2 on page 9 of its data sheet to I am debugging the proto now. When I use only channel 1Y to drive a led, the led is very weakly driven, According to my experience with this LED, the driving current is less than 5mA. At the begining, I use 47 ohm current to limit the current. Since it is too weak, I replace 47ohm with 0 ohm to drive led directly. 1A is connected to microcontroller output. I don't know what is could be wrong.

over 6 years ago

0 Emrys Maier over 6 years ago

TI__Guru* 96712 points

Hi Kelly,
Please provide a schematic of your circuit. This device can very easily drive 5mA, and if connected with 47 ohms (at 5V?) would produce an output current of up to 107mA. This would likely destroy the LED.

Most LED's need ~10mA to operate, and a 330 ohm resistor is best to use in series with them.

0 Kelly Wang over 6 years ago in reply to Emrys Maier

Intellectual 550 points

Emrys,

Thank you very much for your reply. I test another board with 165ohm resitor in series with led and found that it is same as using 47ohm and 0 ohm. I tested the LED using multimeter and it shows Led is still working. I have not be able to figure it out yet. Please see attached schematic of this led driver.

Best Regards,

Kelly

0 Emrys Maier over 6 years ago in reply to Kelly Wang

TI__Guru* 96712 points

Hi Kelly,
Your image did not display.

0 Kelly Wang over 6 years ago in reply to Emrys Maier

Intellectual 550 points

Hi, Emrys,

Please see attached PDF for schematic. Hope you can view it this time.

Thank you very much.RGB driver schematic.pdf

0 Kelly Wang over 6 years ago in reply to Kelly Wang

Intellectual 550 points

SML-LX0402SOC-TR_used on switched by SI.pdfEmrys,

Currently, I am using output 1Y to drive led SML-lx0402S0C. Its data sheet is attached. This led is connected between LED_R and GND.

0 Emrys Maier over 6 years ago in reply to Kelly Wang

TI__Guru* 96712 points

Hi Kelly,
Everything looks correct in the schematic for driving an LED with the SN74LVC3G34. I would recommend taking a close look at everything in the current loop for the LED -- how is the ground connected to the supply? Are there any weak connections/nodes? Double check resistor values... etc.

Based on the schematic, it should be working.

Logic

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SN74LVC3G34: SN74LVC3G34DCUR driving capacity