SP7616ER-LSLASHTR datasheet(6/9 Pages) SIPEX

6 / 9 page

Mar 22-07 RevD

SP7616: Low Side LED Driver



2007 Sipex Corporation

- -

THEORY OF OPERATION

Introduction

The SP7616 is a four-channel constant current

source LED driver with programmable output

current level. The design consists of a regulator

reference voltage source, current amplifier, and

output driver. The precision reference voltage

ensures good performance over voltage and

temperature. The four outputs are tightly coupled

allowing for excellent LED current matching.

Setting LED current

The LED current is set through the Iset resistor.

The SP7616 provides an internal reference voltage

that is set to 1V at the Iset Pin (Pin3). R

SET is then

determined by using equation 1.

RSET = VI

SET *I

MULT/ILED (kΩ),

(1)

Where

SET is the internal reference (1V)

MULT ISET Current Multiplication

Ratio

ILED is the desired Led current.

In example 1: For a 20mA LED current, the current set

resistor should be

RSET=1V*950/20mA (kΩ),

RSET=47.5K

PWM Dimming

The LED dimming control is done through the PWM

pin. The acceptable frequency range of this signal

is 100Hz to 5kHz. The acceptable duty cycle range

of the signal is 10% to 90% at 1KHZ. When the

PWM pin is driven low, only the LED current

sources are disabled while the rest of the chip is

still enabled. .

Analog dimming control

Besides digital PWM control, the LED current can

be controlled continuously (from high to low LED

current) by raising the voltage at the bottom of RSET

from 0.0V to 1V maximum.

RSET value may be

determined from equation 1. Equation 2 shows the

effect of using a VMOD in the circuit on the Led

current

ILED = (1V – VMOD)*IMULT/RSET mA

(2)

Where

1V typical ISET pin voltage

IMULT ISET Current Multiplication

Ratio

ILED is the desired Led current.

VMOD is the adjustment voltage

VMOD is an adjustment voltage applied to the bottom

side of RSET, 950 is a typical current multiplication

ratio IMULT, and ILED is a required LED current in

mA/channel.

Figure 1 shows the location of the

external VMOD source.

Figure 1

If adjustment voltage VMOD is not used, RSET resistor

should be connected to ground.

Shutdown using ISET pin

In normal operation, the voltage at ISET pin is

around 1V. To ensure fast turn on at low duty cycle

and high PWM frequency, only the output drivers

are switching in PWM mode. However, the whole

chip can be shutdown by pulling the voltage at ISET

up to 3V minimum.

VCC pin Considerations

VIN of the SP7616 (Pin 1) needs to be connected to

the anode of the LED for proper operation

Unused Channels and LED 2 Channel (pin 7)

LED 2 channel should never be grounded or left

unconnected it should always be used during

operation.

Other unused channels can be tied to the ground to

save on power consumption.

Shorted LEDs

If all LEDs on a string are shorted, the LED cathode

voltage will be VIN. It is still a working condition for

this

device

but

significantly

increases

the

dissipated power.

At 20mA LED current and VIN = 30V additional

power dissipated in the package is equal to 600mW

that will increase die temperature to 59

0C/W x 0.6W

= 35.4

0C, where 590C/W is 2x3 mm DFN package

thermal

resistance.

Assuming

that

all

other

channels are working at VLED =1.5V the die

temperature will be approximately 41

0C above

ambient temperature and that decreases operating

temperature range. Also to protect the part if too

SP7616ER-L/TR 数据表(PDF) 6 Page - Sipex Corporation

SP7616ER-L/TR 数据表(HTML) 6 Page - Sipex Corporation

Html Pages

1 2 3 4 5 6 7 8 9

数据表下载