SP7614EC6-LSLASHTR datasheet(11/14 Pages) EXAR

11 / 14 page

Jan 09 -08 RevT

SP7612/7614 Low Dropout Linear LED driver

Page 11

SP7612 SP7614

When using white or blue low VF LEDs, and

utilizing the driver's low voltage drop, only 3.4V VIN

is needed for the full 20mA LED current. At 3.1V,

there is still 5mA of typical current available for the

LEDs.

The single cell Li-

Ion battery is utilized in many

applications like cell phones or digital still

cameras. In most cases, the Li-

Ion battery voltage

level only goes down to 3.0V, and not down to the

full discharge level (2.7V) before requesting the

charger.

VDROP < 0.3V. This is the dropout voltage for the

SP7611A.

- VF = 3.1V.

Low VF white LED forward voltage

drop

- VIN (at 20mA) needs to be greater than

(VDROP+VF)

3.1V+.3V= 3.4V

Key Advantages

1) No boost circuit needed for the LCD or

keyboard backlight.

2) Drivers directly connected to a Li-

Ion battery.

3) No EMI, no switching noise, no boost converter

efficiency loss, 1 capacitor, and no inductor.

Example 2:

Drive high VF white or blue LEDs from existing

bus ~ 4.0V to 5.5V

High VF LEDs have a forward voltage drop in the

range of 3.2V to 4.0V. In order to drive these LEDs

with the maximum current of 20mA, enabling

maximum brightness usually requires a boost

circuit for a single cell Li-

Ion power supply. The

SP761X series is capable of driving high VF white

or blue LEDs with its ultra-low dropout feature.

The VIN needs to be only 300mV higher than the

highest VF in the circuit.

- VDROP < 0.3V. Dropout voltage of the SP7611A

- VF (at 20mA) < 3.3V to 4.0V (High VF)

- VIN (at 20mA) = VDROP + VF = 3.6V to 4.3V

- VIN (at 5mA typical) ~ 3.3V

Where VIN = Existing bus = 3.3V to 4.3V

Key Advantages

1) No boost circuit needed for the LCD or

keyboard backlight.

2) Drivers utilize existing bus.

3) Ultra-low voltage drop provides the full 20mA

LED current at the lowest possible voltage level.

LED Brightness Control

The SP7612/4 LED Drivers feature analog and

PWM controls to give designers flexible

brightness control. To determine the value of

RSET , use the "

ISET vs. VCRTL" graph under

the Typical Performance Characteristics.

1. SP7612/4

Analog using VCONTROL

Set VCONTROL and RSET for LED current

SETTING THE LED CURRENT – page 8

- PWM - Vcontrol

-Amplitude of PWM signal sets maximum LED

current

-Pulse width controls current between 0 and

maximum LED Set current

PWM using Enable

Set VCONTROL and RSET for LED current

SETTING THE LED CURRENT – page 6

ENABLE = PWM

-Amplitude has no effect on current

-Pulse width controls current between 0 and

maximum LED set current

SP7614EC6-L/TR Datasheet(PDF) 11 Page - Exar Corporation

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