ZXLD1370

ZXLD1370

Document number: DS32165 Rev. 4 - 2

24 of 36

www.diodes.com

March 2011

© Diodes Incorporated

A Product Line of

Diodes Incorporated

PWM OUTPUT CURRENT CONTROL & DIMMING

The ZXLD1370 has a dedicated PWM dimming input that allows a wide dimming frequency range from 100Hz to 1kHz with

up to 1000:1 resolution; however higher dimming frequencies can be used – at the expense of dimming dynamic range and

accuracy.

Typically, for a PWM frequency of 1kHz, the error on the current linearity is lower than 5%; in particular the accuracy is

better than 1% for PWM from 5% to 100%. This is shown in the graph below:

Buck mode - L=33uH - Rs = 150m

Ω - PWM @1kHz

0.00

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0

10

20304050

60

7080

90

100

PWM

0%

1%

2%

3%

4%

5%

6%

7%

8%

9%

10%

PWM @ 1kHz

Error

Figure 28: LED current linearity and accuracy with PWM dimming at 1kHz

For a PWM frequency of 100Hz, the error on the current linearity is lower than 2.5%; it becomes negligible for PWM greater

than 5%. This is shown in the graph below:

Buck mode - L=33uH - Rs = 150m

Ω - PWM @100Hz

0.00

250.00

500.00

750.00

1000.00

1250.00

1500.00

0

1020

3040506070

8090

100

PWM

0%

1%

2%

3%

4%

5%

6%

7%

8%

9%

10%

PWM @100Hz

Error

Figure 29: LED current linearity and accuracy with PWM dimming at 100Hz

The PWM pin is designed to be driven by both 3.3V and 5V logic levels. It can be driven also by an open drain/collector

transistor. In this case the designer can either use the internal pull-up network or an external pull-up network in order to

speed-up PWM transitions, as shown in the Boost/ Buck-Boost section.