ZXLD1371Q

ZXLD1371Q

Document number: DS37116 Rev. 1 - 2

32 of 42

www.diodes.com

September 2015

© Diodes Incorporated

ZXLD1371Q

PWM Output Current Control & Dimming

The ZXLD1371Q 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 log

ic 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 = 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

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