ATtiny13a Driver Circuit Help

I'm an Arduino/Atmel fan and have started looking at flashlight drivers as a way to combine my interest in physical computing and flashlights. I keep seeing a circuit pattern that hurts my head and am wondering if anyone can explain it to me.

The circuit (borrowed from DX wiki):


Similar:


It clearly shows pin 6 of an Atmel ATtiny13a being routed to the voltage/current source (Vdd) on 3 AMC7135 current regulators. Each regulator produces a constant 350ma from this source and this is where I'm scratching my head.

The I/O pins on an ATtiny13a can not source or sink more than 40 mA per pin but the diagram seems to indicate it is sourcing 1050ma (350ma to each of 3 AMC7135). Using PWM on that pin produces different modes but I'm just not sure how the AtTiny is manipulating > 1A of power on one of its I/O pins without a fet / transistor.

Hi Denos!

The 7135 is the current sink. The Amtel chip is only driving the Vdd pin with a PWM signal to give different power levels. Hope this helps!!

After reading your response, I found this image:


Would it be correct to say that current passes through the LED, into Vout where it is restricted to 350ma (sink) and out to ground? Vdd ties to some internal fet/transistor that enables or disables the flow from Vout to ground?

http://www.micro-bridge.com/data/ADD/AMC7135.pdf

There you go , a internal fet .

Vdd tied hi is like having the throttle floored in the car at 350mph, anywhere from zero to high is adjusting the throttle there-fore the current 0-349mph , the tiny chip output is varying the vdd/input using PWM in a fast on/off style and all the work is done by the 7135 up to its limit of 350mph .

Car talk , yuk!