ZXLD1371

ZXLD1371

Document number: DS35436 Rev. 1 - 2

33 of 42

www.diodes.com

February 2012

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PWM Output Current Control & Dimming

The ZXLD1371 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:

Figure 10. 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:

Figure 11. 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 and as such doesn’t require open collector/drain

drive. It can also be driven 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.

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

Ω - PWM @1kHz

0.00

250.00

500.00

750.00

1000.00

1250.00

1500.00

0

10

20304050

607080

90

100

PWM

0%

1%

2%

3%

4%

5%

6%

7%

8%

9%

10%

PWM @1kHz

Error

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

80

90

100

PWM

0%

1%

2%

3%

4%

5%

6%

7%

8%

9%

10%

PWM @ 100Hz

Error