AP8800EV1

Issue 3 – August 2009

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© Diodes Incorporated 2009

3

AP8800EV1 EVALUATION BOARD

REFERENCE DESIGN

The AP8800EV1 is an evaluation board configured to be used with the AP8800 in SOP-8L package.

The target application is a driver for one or more series-connected LEDs for luminaires in both

commercial and automotive applications.

The maximum operating voltage for the evaluation board is 28V, and a 0R33 sense resistor R1 sets

the nominal current at 300mA.

An accurate way of determining the current, avoiding the need to insert an ammeter in the current

path, is to measure the voltage on the sense resistor. A 10K resistor and a 1uF capacitor can be used

to form a low pass filter and the voltage across the capacitor represents a more stable dc reading of

current. Using this method, 100mV represents 0.3 Amp when using a 0R33 sense resistor.

The CTRL pin connects to a low pass filter within the AP8800 chip to provide some decoupling, but

the external capacitor C2 (100nF) can be used to provide additional decoupling to reduce any high

frequency noise as well as providing soft start function.

Both DC and PWM dimming can be achieved by driving the CTRL pin. For DC dimming, the CTRL pin

may be driven between 0.3V and 1.25V. Driving the CTRL pin below 0.2V will shut down the output

current. For PWM dimming, an external open-collector NPN transistor or open-drain N-channel

MOSFET can be used to drive the CTRL pin. The PWM frequency can be around 100Hz to 1 kHz.

For better resolution, PWM capacitor C2 should be removed on the evaluation board, to give a more

Shorting R2 will connect the test pin CTRL to device pin CTRL if needed. The external capacitor C2

on the CTRL pin sets the soft start time. The amount of soft start time achievable is approximately

0.5ms/nF.

For other reference designs or further applications information, please refer to the AP8800 datasheet.