LX1991EVALKIT - Microsemi Corporation

LX1991 EVALUATION BOARD

USER’S GUIDE

LX1991 Six Output Programmable LED Current Sink

INTEGRATED PRODUCTS

LX1991 EVALUATION BOARD USER GUIDE

Rev. 1.0 1/8/03 Integrated Products

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

TABLE OF CONTENTS

Overview .....................................................................................................................................................................3

Features

Operation

TABLES

Evaluation Board Connections ..............................................................................................................3

Jumper Explanation.................................................................................................................................4

Test Point Descriptions...........................................................................................................................4

FIGURES

LX1991 Evaluation Board Component List............................................................................................5

LX1991 Evaluation Board Silk Screen............................................................................................ ........5

LX1991 Evaluation Board Schematic.....................................................................................................6

LX1991 EVALUATION BOARD USER GUIDE

Rev. 1.0 1/8/03 Integrated Products

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

OVERVIEW

The LX1991 six channel current sink driver is

ideal for controlling brightness of high quality

dimmable LED’s. 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 six (Microsemi

UBLED470A) white surface mount LED’s whose

cathodes are connected to each sink output of

the LX1991. The anodes of the LED’s are

connected together to a test point called VLOAD

which the user can connect to an external

voltage source (typically 5V, maximum is 40V)

LED6 requires an external jumper between TP7

and TP8 to allow current to flow. This

demonstrates that one or more channels can be

left open without effecting the other channels. In

addition these test points allow the easy addition

of a application specific load or a current probe

loop. Use of a current probe will allow easy

viewing of the current rise and fall times.

A small rheostat (Current Adjust) in series with

R8 (1.02K which sets the maximum current at

30mA) varies the RSET resistance such that the

output LED currents will vary from about 1.5mA

to 30mA. Two other jumpers are included,

EXT_EN which enables/disables the LX1991,

and PWM_IN which allows an externally

supplied PWM signal to toggle the DIG_DIM

input to allow duty cycle dimming.

Evaluation Board Feature s

• One channel is left open for application

specific loads to be added or current

probe loop

• Included rheostat allows output current to

be set from 1 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. In the simplest configuration connect 5V

to both EXT VDD and VLOAD and the common

(ground return) to RTN. With power connected

to these two pins and the a jumper (factory

installed) between PWM_IN and PULL-UP the

evaluation board should be operational. The

LX1991 integrated circuit itself requires a input

supply voltage (EXT VDD) in the range of 4.5 to

5.5V. When using the included white LED’s a

supply voltage of at least 4V is required on the

VLOAD input depending on the current setting

(current adjust). All inputs are described in table

1 below.

The other two inputs PWM_IN and ENABLE

allow external control over dimming and

shutdown. The evaluation board comes with a

built in 10K pull-up resistor R1 that is connected

between the ENABLE input and EXT VDD. R1

will enable the device unless a jumper is placed

between EXT_EN and RTN (GND).

Input Allowable Range Description

EXT VDD 4.5 to 5.5V LX1991 power supply. Quiescent current draw i s between 4 and

13mA depending on voltage and tempe rature and the programmed

output sink currents

VLOAD 3 to 40V (5V typ.)

LED voltage supply. Required voltage depen ds on forward voltage

requirements of LED’s an d 700-1000mV chip overhead. This

current will vary between 9 and 180mA depen ding on the

programmed output sink current and if all six LED are connected.

EXT_EN 0 to VDD Input for external enable control, board ships with 10K pull-up to

EXT VDD

PWM_IN 0 to VDD Input to allow duty cycle dimming of output 150hz to 100Khz logi c

signal, active high

RTN/GND 0V Common ground reference

Table 1 – Evaluation Board Connections

LX1991 EVALUATION BOARD USER GUIDE

Rev. 1.0 1/8/03 Integrated Products

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

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 10K pull-up resistor low (less than

0.8V).The PWM_IN header input allows an

external PWM signal to control the output

current by duty cycle dimming. This is

accomplished by switching the device’s

DIG_DIM input with a logic signal. The

practical limit to this switching frequency is

about 100Khz, at frequencies greater than this

internal delays will add errors to the expected

output duty cycle. The evaluation board comes

with a 470pF CSLOPE capacitor. This value

can be increased to vary the rise and fall times

of the output current waveform. For greater

detail see the LX1991 datasheet.

Test Points SINK1 to SINK6 allow you to

monitor the voltage drop across these pins to

ground. This voltage will change to maintain the

correct forward voltage across the LED’s for the

programmed sink current. It can range from as

low as 400mV to 40V when the outputs are off

depending on the VLOAD supply voltage.

The various jumper positions are summarized in

table 2 and test points in table 3. The factory

installed active and passive components list can

be found in table 4. Following the two tables

you will find the PCB silkscreen figure 1 and the

circuit schematic in figure 2. All necessary PCB

traces and components are on the topside of the

board. However there are PCB traces and

silkscreen on the bottom side that when

populated is used for a special version of the

evaluation board that is used internally by

Microsemi for training and demonstration

purposes.

Jumper Function

PWM_IN Jumper to PULLUP connects PWM_IN through a 10K pull-up resistor to EXT VDD, Jumper

to RTN connects PWM_IN to Ground. Open allows hookup to external PWM source.

EXT_EN Jumper to RTN disables the LX1991 by pulling down on the 10K pull-up re sistor ; EXT_EN

open enable the LX1991 throug h the 10K pull-up to EXT VDD

Table 2 – Jumper Explanation

Test

Point Description

VLOAD VLOAD Input, power suppl y to LED’s (3 to 40V)

RTN/GND Common Ground Reference

EXT VDD VDD Input to LX1991 (4.5 to 5.5V)

EXT_EN ENABLE input can be connected to external enable signal; high o r floating is on, low is

off (LX1991 pin 16)

SINK1 SINK1 (LX1991 pin 3)

SINK2 SINK2 (LX1991 pin 4)

SINK3 SINK3 (LX1991 pin 6)

SINK4 SINK4 (LX1991 pin 7)

SINK5 SINK5 (LX1991 pin 8)

SINK6 SINK6 (LX1991 pin 10)

PWM_IN PWM Input can be connected to external pulse generator for duty cycle dimming

(LX1991 pin 1) Table 3 – Test Point Descriptions

LX1991 EVALUATION BOARD USER GUIDE

Rev. 1.0 1/8/03 Integrated Products

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

LX1991 EVALUATION BOARD COMPONENT LIST

MISCELLANEOUS COMPONENTS

Part Description Manufacturer & Part # Reference

Designators Qty

IC, Controller MICROSEMI LX1991ILM U1 1

LEDs, BLUE Bright Microsemi UBLED470A

Optomite or equivalent LED1 - LED6 6

Probe Standoffs Various 8

CAPACITORS

Part Description Manufacturer & Part # Reference

Designators Qty

Capacitor, X7R, 100nF, 50V, 10% Any C3, C4 2

Capacitor, CGO, 470pF, Any CSLOPE 1

RESISTORS

Part Description Manufacturer & Part # Reference

Designators Qty

Resistor, Pot Thumbwheel 20K Any Current Adjust 1

Resistor, 1.02K, 1%, 1/16W Any R8 1

Resistor, 10K, 1%, 1/16W Any R1,R6 2

Not Used n/a R7 0

LX1991 EVALUATION BOARD SILKSCREEN

TP8

LED4

LED5

LX 1991 EV AL

LED6

LED3

TP7

Sil k sc r e en Top RR

GND

PWM

LX1991 SIX OUTPUT PROGRA MMABLE LED CURRENT

EXT V DD

LED1

SIN K E V ALUATION BO A RD

LED2

Vload

Cu r r e nt Adjust

EXT_EN

RTN

SINK6

SINK5

SINK4

SINK3

SINK1

SINK2

GND

RTN

CSLOPE

RTN

PULL

Figure 1

LX1991 EVALUATION BOARD USER GUIDE

Rev. 1.0 1/8/03 Integrated Products

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

LX1991 EVALUATION BOARD SCHEMATIC

EXT VDD

RTN

10K

PWM INPUT

GND

VDD

DIG_DIM

SINK1

SINK2

N/C

ISET-

SINK6

GND

SINK3

SINK4

SINK5

ISET+

N/C

CSLOPE

LX1991LQ

10K

CSLOPE

470pF

1.02K

R7*

Current

Adjust

20K

GND

LED6

LED5

LED4

LED3

LED2

LED1

5678

13141516

SINK1 SINK2 SINK3 SINK4 SINK5 SINK6

1.0µF

VLOAD

RTN

1.0µF

EXT_EN

RTN

TP7

TP8

PULL UP

* A resistor may be added to

limit the current to an application

specific range

Figure 2 – Schematic