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The specs of TI TLC5944 LED driver says "constant current sinking" capability is 60-mA.(LED Power supply voltage up to 15 Volts, and Vcc=3.0V to 5.5 V )

My understanding is if Sink current is low, then its better as it will not heat-up my LED driver chips.

1- I want to understand What is the importance of High (or Low) LED driver Sink current?

2- Why we do not talk about sourcing Current instead?

Any comments?

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The current value depends on the led requirement, you should drive the leds with the proper current to have the desired luminosity, the device you are talking about actually can change this current to have different luminosity levels. The 60mA of the device is the maximum the device can lead. They talk about sinking current because the led are connected to the VCC and the device "ground" the LED to switch it on, so the current flows inside the LED and "sink" into the device.

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In general, ICs tend to be better at sinking current than sourcing current. Hopefully someone with more IC design experience will be able to answer why.

More current sinking capability doesn't automatically translate to higher heat dissipation; it's all about how much resistance the output drivers have. Mosfet drivers often have on-state resistances in the tenths of ohms and can switch hundreds of Amps without getting warm if driven correctly, but generally speaking LED drivers aren't quite this robust.

The sink or source current capability of a driver gives you an idea of what it can be used for. 60mA will give you plenty of capability to light regular old LEDs, but probably won't work very well to light a bunch of them, or to activate relays or incandescent light bulbs. It's important to also keep in mind what the voltage capability of the driver is (60mA at what voltage?) as well as to know what the total current capacity (or power dissipation capacity) of the port or chip is. The classical example given is the PIC processor; each pin can sink or source 20mA of current, but the entire 8-bit port can only sink or source 100mA of current, if I remember correctly. These numbers help you design your circuit so that you don't exceed the capacity of the device.

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  • \$\begingroup\$ LED Power supply voltage up to 15 Volts, and Vcc=3.0V to 5.5 V \$\endgroup\$ – gpuguy Dec 17 '12 at 12:04
  • \$\begingroup\$ If all you're looking for is a compact way to drive LEDs you could always use the old (i.e. cheap) ULN200x drivers; each one of those has seven drivers with differing bias arrangements, 500mA drive PER OUTPUT and 50V withstand capability. Digikey has then in onsie-twosie prices at $0.57. \$\endgroup\$ – akohlsmith Dec 17 '12 at 12:16

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