SP7612 datasheet(6/9 Pages) SIPEX

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Date: 6/30/04

SP7611A/7612/7614 Low Dropout LED Driver for Any Color LED

Example 2: Drive high VF white or blue LEDs from

existing bus from 4.0V to 5.5V

High VF white or blue LEDs have forward voltage drop in

the range of 3.2V to 4.0V. To drive these LEDs with the

maximum current of 20mA for maximum brightness,

usually requires a boost circuit for a single cell Li-ion

voltage range. In some cases, there is already a voltage

bus in the system, which can be utilized. Due to the ultra-

low voltage drop of the SP761X series of LED drivers to

drive high VF white or blue LEDs. The VIN needs to be

only 300mV higher than the highest VF in the circuit.

APPLICATION INFORMATION

- TDROP < 0.3V

- 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 utilizes existing bus

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

current at the lowest possible voltage level.

Example 3: Drive white, blue red, amber LEDs string

Assuming boost circuit, or existing voltage bus, the

SP761X series of LED drivers can be used to drive a

whole string of LEDs and flexible brightness control -

analog and/or PWM.

- VDROP < 0.3V

- VIN_MIN = N x VF + VDROP

- VIN_MIN = N x VF + 5.5V

Where VIN = Existing bus, boost Voltage

Key Advantages

1) No need for current matching resistors and discrete

transistor for brightness control

LED Brightness Control

All of the SP761X LED Drivers feature analog and PWM

controls to give designers flexible brightness control.

These control methods can be applied to the circuit in two

different ways, to provide more flexibility than any other

solution. To determine the value of RSET, use the "ISET vs.

VCRTL" graph under the Typical Performance Character-

istics.

1. SP7611A

VIN

LED1

GND

CTRL

ON/OFF

ENABLE

VCONTROL 3V

RSET

SP7611

I SET

LED3

LED2

LED4

- Analog

Set VCONTROL and RSET for LED current

ILED = 200 x (VCONTROL - VCNTR) / RSET

- PWM

VCONTROL = PWM

-Amplitude sets maximum LED current

-Pulse width controls between 0 and maximum

2. SP7612

VIN

LED1

GND

CTRL

ON/OFF

ENABLE

VCONTROL

RSET

SP7612

I SET

LED3

LED4

VIN

LED1

GND

CTRL

ON/OFF

ENABLE

VCONTROL

RSET

SP7611

I SET

LED3

LED2

LED4

LED1

GND

CTRL

ON/OFF

ENABLE

VCONTROL

RSET

SP7611

I SET

LED2

LED4

‘N’number of LEDs Per Branch

LED3

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