STLD40DPMR datasheet(8/14 Pages) STMICROELECTRONICS

8 / 14 page

Functional description

STLD40D

8/14

Functional description

5.1

Boost controller

The STLD40D is a Boost converter operating in PFM (pulsed frequency modulation) mode.

The converter monitors the LED current through the resistor RLED and when the feedback voltage falls

below the reference voltage REF2, the boost switch TSW turns ON and the current ramps up. The

inductor current is measured by sensing the temperature compensated drain voltage of the boost

MOSFET. The boost turns off when its drain voltage reaches the internally reference REF1, the main

switch remains off until the minimum off time (250ns typical) has passed and the feedback voltage is

below the reference again. A maximum ON time of 4µs typical prevents the switch TSW to stay ON during

a too long period of time.

5.2

Adjustable peak inductor current limit

The peak inductor current is monitored by sensing the drain voltage of the switch TSW. Since it exceeds

the temperature compensated and supply voltage compensated reference REF1, the RS Flip flop is reset

and TSW is turned OFF. By connecting a resistance to the pin RSET the peak current limit can be adjusted.

from 200mA to 1A. When RSET resistor value is about 12kΩ is connected directly to GND, the default

value is 1A.

5.3

Enable

The ENABLE pin is a high logic input signal and allows turning on/off the controller without cutting the

input voltage from the boost regulator circuit. The pin ENABLE can be used to dim the LED by applying a

low frequency PWM signal.

5.4

OVP

If the regulation loop is cut, there is no signal at the feedback pin, the PFM controller will then continue to

switch without control and generate an output voltage at the SW, and VO pin exceeding the breakdown

value VBSW, and VBO.

The Over Voltage Protection (OVP) senses the voltage at the VO pin. When the voltage exceed 38V Min

the controller is automatically turned OFF.

A hysteresis control allows the device restarting automatically since the output voltage drops down of

1.5V.

STLD40DPMR 数据表(PDF) 8 Page - STMicroelectronics

STLD40DPMR 数据表(HTML) 8 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14

数据表下载