L99LD01 datasheet(18/69 Pages) STMICROELECTRONICS

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Functional description

L99LD01

18/69

DocID025319 Rev 3

and RSLOPE and RT are defined in the Figure 8, together with their typical values.

Therefore, will result:

and consequently:

where T is the period of the converter oscillator.

The additional compensating current slope can be simply adjusted by properly setting the

value of the external resistor R9 (and consequently RT).

Figure 8. Internal structure of the slope compensation circuit

2.2.3

LED chain overvoltage detection

Via the external resistor divider (R5, R6) it is possible to detect LED overvoltage events, by

programming a threshold for the maximum drop voltage of the LED chain for a specific LED

board (see Section 2.2.12 for details). In case Boost or Fly back topology is used, the

LMODE pin must be connected to GND. In this case the voltage at pin VLED will be referred to

ground. Instead, if Buck Boost topology is used, the LMODE pin must be connected to 5 V or

left open. An internal pull up current source keep this pin high, and in this case, the voltage

applied by the resistor divider R5/R6 at pin VLED will be referred to the battery voltage

applied at pin VS. If a valid overvoltage event occurs, which is detected if the LED drop

voltage reaches a value VLED ≥ OV_TH1, the device is switched off immediately forcing the

OSC

----------------

⋅

ADD

OSC

SLOPE

-----------------------

⋅⋅

ADD

---------------

OSC RSLO PE

⋅⋅

T T

⋅

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