Detailed description

STLDC08

14/29

Doc ID 18476 Rev 1

7.3

Over voltage protection (OVP)

As with any current source, the output voltage rises when the output gets high impedance or

is disconnected. To prevent the output voltage exceeding the maximum switch voltage rating

of the main switch, an overvoltage protection circuit is integrated. As soon as the output

voltage exceeds the OVP threshold, the converter stops switching and the output voltage

drops. When the output voltage falls below the OVP threshold, the converter continues

operation until the output voltage exceeds the OVP threshold again.

7.4

Enable/PWM

The enable pin allows disabling and enabling of the device as well as brightness control of

the LEDs by applying a PWM signal. In order to avoid visible flicker, the frequency of the

PWM signal should be higher than 120 Hz. Changing the PWM duty cycle therefore

changes the LED brightness.

Figure 17.

Timing diagram

V

CC

2VCC

DRV

PWMOUT

V

OUT

I

CC

ILED

Charge Pump

active

STLDC08 supplied by

V

OUT

V

flowing through the LEDs

V

supplied by V

OUT

Follows EN/PWM

input

Soft start cycle ended,

PWMOUT is realeased

1.7 V

1.9 V

AM07847v1

V

CC

2VCC

DRV

PWMOUT

V

OUT

I

CC

ILED

Charge Pump

active

STLDC08 supplied by

V

OUT

V

flowing through the LEDs

V

supplied by V

OUT

Follows EN/PWM

input

Soft start cycle ended,

PWMOUT is realeased

1.7 V

1.9 V

AM07847v1