SP7614A datasheet(9/14 Pages) SIPEX

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Apr20-07 RevS

SP7611A/7612A/7614A Low Dropout Linear LED driver



2007 Sipex Corporation

Page 9

applications. Any of the SP761X series of LED

drivers can be used in the applications presented

in this document, due to their similar operation.

Example 1:

Drive low VF white or blue LEDs directly from

single cell Li-Ion

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.

Example 3:

Drive white, blue, red, amber LED string

In a boost circuit, or existing voltage bus, the

SP761X series of LED drivers can be used to

drive a whole string of LEDs and achieve flexible

brightness control - whether using analog or PWM.

VDROP = 0.3V. Dropout voltage of the SP7611A

- VIN_MIN = N x VF + VDROP

- VIN_MIN = N x VF + 0.3V

Where VIN_MIN = Existing bus, boost Voltage

‘N’ number of LEDs Per Branch

VF = Forward voltage of the LED

Key Advantages

1) No need for current matching resistors

and discrete transistors for brightness

control.

APPLICATION INFORMATION

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