ZXLD1370

Document number: DS32165 Rev. 6 - 2

27 of 40

www.diodes.com

December 2016

© Diodes Incorporated

ZXLD1370

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 = 150mΩ - PWM @ 1kHz

0.00

250.00

500.00

750.00

1000.00

1250.00

1500.00

0

10

20

30

40

50

60

70

80

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 = 150mΩ - PWM @ 100Hz

0.00

250.00

500.00

750.00

1000.00

1250.00

1500.00

0

10

20

30

40

50

60

70

80

90

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 and Buck-Boost section.