L99LD01 datasheet(9/69 Pages) STMICROELECTRONICS

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L99LD01

Functional description

2.1.2

Stand alone operation

The device operates with default parameters. The overall tolerance depends on the internal

references precision and the external resistors tolerance. In details:

•

LED current via external sensing resistor:

•

Maximum input current via an external shunt resistor.

•

Oscillator dither effects are set to its default parameters; a low level on the SDI allows

disabling the function.

•

Low frequency dimming operation is allowed either by PWM pin or by logic level

PWM_L input pin. Connecting the PWM control pin to the supply voltage via a resistor

divider, allows the converter to be synchronized to the low frequency PWM generated,

i.e., from the smart junction box.

•

Connecting the MOUT pin, which by default provides a logic level image of the control

input, to the PWM_L input, it is possible to drive the LED according to the PWM

frequency and duty cycle of control. (See application circuit of Figure 38).

•

In case of VR1 over temperature, its output will be permanently switched off. The device

still continues to work in normal mode but with VR1 =OFF.

The L99LD01 can operate in 4 different modes:

•

Start-up fail

•

Normal mode

•

Software limp home

•

Limp home

After the power on reset, the device stays in start-up phase until VCC1 reaches a specified

threshold, VCC1_TH. Then the device enters in normal mode either with microcontroller or

standalone, depending on the voltage level on the Nreset pin.

Note:

The information about the operation with microcontroller or standalone is latched until a new

power on reset.

If VCC1 does not reach both VCC1 fail and VCC1_TH thresholds within a given delay or if a

VCC1 over temperature event occurs, the device enters in a corresponding state.

2.1.3

Start-up fail

The device enters this mode in case a VCC1 under voltage event occurs during start-up

phase and VS < VSMIN, provided that a microcontroller is detected. In this case VCC1 is

turned off.

If VS remains below VSMIN, then the converter is switched off.

If VS rises above VSMIN, the converter behaves according to the PWM_L pin.

LED

150 mV/R

SENSE

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