LX1990-02 EVAL

LX1990-02 EVAL Datasheet

LX1990 EVALUATION BOARD USER’S GUIDE

Part	Datasheet
LX1990-02 EVAL	LX1990-02 EVAL (pdf)

Related Parts	Information
LX1990-03EVAL	LX1990-03EVAL

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LX1990 EVALUATION BOARD USER’S GUIDE LX1990 Dual Programmable LED Current Sink INTEGRATED PRODUCTS W.Microsemi .C O M LX1990 EVALUATION BOARD USER GUIDE TABLE OF CONTENTS 3 Features Operation TABLES Evaluation Board Jumper Explanation Test Point Descriptions FIGURES LX1990 Evaluation Board Component List LX1990 Evaluation Board Silk Screen LX1990 Evaluation Board LX190 USER GUIDE Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax 714-893-2570 W.Microsemi .C O M LX1990 EVALUATION BOARD USER GUIDE OVERVIEW The LX1990 is a dual output current sink optimized for driving light emitting diodes. The evaluation board demonstrates how this low cost bipolar IC enables precise current regulation in LED display lighting applications, yet requires far fewer parts than discrete solutions. The evaluation board ships with two strings of three LED’s each. Two green and one blue connected in series to each output. Each LED has a parallel connected jumper JB2-JB7 that allow the LED to be bypassed to remove it from the circuit so various combinations of LED’s can be easily configured for each series string. A small rheostat R1 in series with R2 4.32K which sets the maximum current at 30mA varies the RSET resistance such that the output LED current will vary from about 5mA to 30mA. Two other jumpers are included, JB1 which enables the LX1990, and JB8 to which allows an externally supplied PWM signal to toggle the RSET resistance to allow duty cycle dimming. Evaluation Board Features • Easily configured with 1 to 3 LED’s on each output • Included rheostat allows output current to be set from 5 to 30mA • Jumpers allow external PWM signal to burst dim the LED’s and an external enable control EVALUATION BOARD OPERATION The evaluation board has four possible inputs of which at least two must be used to operate the circuit. These inputs are described in table 1 below. The LX1990 integrated circuit itself requires a input supply voltage VDD in the range of to 5.5V. When using all three LED’s in series a supply voltage of greater than 5.5V is required on the VLOAD input, since the combined forward voltage of the three LED’s at the rated current of 20mA is about 8.4V. However if you were to bypass as an example the two blue LED’s by moving up the shorting blocks on JB4 and JB7 then a single 5V supply could be connected at both VDD and VLOAD to drive the remaining four LED’s or conversely the two blue LED’s since both require a forward voltage of about 4V. If you are willing to drive the blue LED’s at only 5mA then voltages as low as 3.3V will directly drive both the chip and the LED’s. The other two inputs PWM and ENABLE allow external control over dimming and shutdown. The evaluation board comes with a built in 100K pull-up resistor R3 that is connected between the ENABLE input and VDD. R3 will enable the outputs unless JB1 is set to OFF. When JB1 is in the EXT/ON position enable is also connected to the external ENABLE input TP5. An external voltage signal or open collector logic can be applied to this point to disable the device. This external signal must be able to drive the 100K pull-up resistor low less than 0.8V . Input VDD VLOAD ENABLE PWM Allowable Range to 5.5V 2 to 10V 0 to VDD 0 to VDD 0V LX1990 power supply. Quiescent current draw is between and 4mA depending on voltage and temperature LED voltage supply. Required voltage depends on forward voltage requirements of LED’s and 100-400mV chip overhead Input for external enable control, board ships with 100K pull-up to VDD Input to allow duty cycle dimming of output 150hz to 20Khz logic signal, active high Common ground reference Table 1 Evaluation Board Connections LX190 USER GUIDE Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax 714-893-2570 LX1990 EVALUATION BOARD USER GUIDE W.Microsemi .C O M The PWM input TP9 engaged by JP8 allows an external PWM signal to control the output current by duty cycle dimming. This is accomplished by switching the ISET current on and off. The practical limit to this switching frequency is about 20Khz, at frequencies greater than this internal delays will add errors to the expected output duty cycle. Q1, R2 and R4 provide an open collector drive for the ISET resistor so a standard pulse generator can be used for evaluation purposes. For greater detail see the LX1990 datasheet.

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LX1990 EVALUATION BOARD USER’S GUIDE

LX1990 Dual Programmable LED Current Sink

INTEGRATED PRODUCTS

W.Microsemi .C O M

LX1990 EVALUATION BOARD

USER GUIDE

TABLE OF CONTENTS
3 Features Operation

TABLES Evaluation Board Jumper Explanation Test Point Descriptions

FIGURES LX1990 Evaluation Board Component List LX1990 Evaluation Board Silk Screen LX1990 Evaluation Board

LX190 USER GUIDE

Microsemi

Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax 714-893-2570

W.Microsemi .C O M

LX1990 EVALUATION BOARD

USER GUIDE

OVERVIEW

The LX1990 is a dual output current sink optimized for driving light emitting diodes. The evaluation board demonstrates how this low cost bipolar IC enables precise current regulation in LED display lighting applications, yet requires far fewer parts than discrete solutions.

The evaluation board ships with two strings of three LED’s each. Two green and one blue connected in series to each output. Each LED has a parallel connected jumper JB2-JB7 that allow the LED to be bypassed to remove it from the circuit so various combinations of LED’s can be easily configured for each series string. A small rheostat R1 in series with R2 4.32K which sets the maximum current at 30mA varies the RSET resistance such that the output LED current will vary from about 5mA to 30mA. Two other jumpers are included, JB1 which enables the LX1990, and JB8 to which allows an externally supplied PWM signal to toggle the RSET resistance to allow duty cycle dimming.

Evaluation Board Features
• Easily configured with 1 to 3 LED’s on each output
• Included rheostat allows output current to be set from 5 to 30mA
• Jumpers allow external PWM signal to burst dim the LED’s and an external enable control

EVALUATION BOARD OPERATION

The evaluation board has four possible inputs of which at least two must be used to operate the circuit. These inputs are described in table 1 below.

The LX1990 integrated circuit itself requires a input supply voltage VDD in the range of to 5.5V. When using all three LED’s in series a supply voltage of greater than 5.5V is required on the VLOAD input, since the combined forward voltage of the three LED’s at the rated current of 20mA is about 8.4V. However if you were to bypass as an example the two blue LED’s by moving up the shorting blocks on JB4 and JB7 then a single 5V supply could be connected at both VDD and VLOAD to drive the remaining four LED’s or conversely the two blue LED’s since both require a forward voltage of about 4V. If you are willing to drive the blue LED’s at only 5mA then voltages as low as 3.3V will directly drive both the chip and the LED’s.

The other two inputs PWM and ENABLE allow external control over dimming and shutdown. The evaluation board comes with a built in 100K pull-up resistor R3 that is connected between the ENABLE input and VDD. R3 will enable the outputs unless JB1 is set to OFF. When JB1 is in the EXT/ON position enable is also connected to the external ENABLE input TP5. An external voltage signal or open collector logic can be applied to this point to disable the device. This external signal must be able to drive the 100K pull-up resistor low less than 0.8V .

Input

VDD VLOAD ENABLE PWM

Allowable Range
to 5.5V 2 to 10V 0 to VDD 0 to VDD 0V

LX1990 power supply. Quiescent current draw is between and 4mA depending on voltage and temperature LED voltage supply. Required voltage depends on forward voltage requirements of LED’s and 100-400mV chip overhead Input for external enable control, board ships with 100K pull-up to VDD Input to allow duty cycle dimming of output 150hz to 20Khz logic signal, active high

Common ground reference

Table 1 Evaluation Board Connections

LX190 USER GUIDE

Microsemi

Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax 714-893-2570

LX1990 EVALUATION BOARD

USER GUIDE

W.Microsemi .C O M

The PWM input TP9 engaged by JP8 allows an external PWM signal to control the output current by duty cycle dimming. This is accomplished by switching the ISET current on and off. The practical limit to this switching frequency is about 20Khz, at frequencies greater than this internal delays will add errors to the expected output duty cycle. Q1, R2 and R4 provide an open collector drive for the ISET resistor so a standard pulse generator can be used for evaluation purposes. For greater detail see the LX1990 datasheet.

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Datasheet ID: LX1990-02EVAL 649015