LDS8710008-T2-250 - Zilog - Datasheet.Live

LDS8710

Characteristics subject to change without notice

High Efficiency 10 LED Driver With No External Schottky

FEATURES

High efficiency boost converter with the input

voltage range from 2.7 to 5.5 V

No external Schottky Required (Internal

synchronous rectifier*)

250 mV current sense voltage

Drives one LED string with 10 LEDs in series

up to 30 mA

0.7 MHz Switching Frequency

Efficiency greater than 83%

PWM LED Dimming Control Mode

Over-voltage, under-voltage, over-current,

and over-temperature protection

Low Shutdown Current (<1µA)

Available in 2 x 3 x 0.8 mm 8-pin TDFN

package

APPLICATION

Color Display Backlight

Portable Navigation and GPS Receivers

Smart phones

Digital Photo Frames

Portable DVD Players

Multimedia Phones

DESCRIPTION

The LDS8710 is a fixed frequency current mode

boost converter with internal synchronous rectifier

and cycle-by-cycle switch current limit specifically

designed to drive a string of up to 10 White LEDs

with factory preset maximum current 20, 25, or 30

mA. Series connection of the LEDs provides constant

current and subsequently uniform brightness,

eliminating the need for ballast resistors and factory

calibration. Operation at 0.7 MHz allows use of small

value low profile inductor (10 – 33 µH) and 1µF 50V

ceramic capacitor.

The use of integrated synchronous rectifier makes

the efficiency dependent on only inductor DC

resistance.

The supply voltage down to 2.7 V for new Li-ion

battery chemistries or two alkaline battery cells

extends the battery life. Under-voltage protection

disables the part when VIN voltage reaches 2.0V

The LDS8710 has thermal shutdown set at 150 0C.

Above this value, the boost converter stops

switching. The part resumes normal operations when

temperature drops below 130 0C.

The over-current protection provides cycle-by-cycle

current limit.

The internal output over-voltage protection prevents

damage in the case of a faulty LED disconnect.

The PWM control ensures brightness adjustment with

a frequency from 100 Hz up to 30 KHz.

The EN/PWM logic input functions as a chip enable

and LED current PWM contol pin.

The device is available in in 8-pin TDFN 2 x 3 mm

package with a max height of 0.8 mm.

TYPICAL APPLICATION CIRCUIT

*) Patent pending

LDS8710

Characteristics subject to change without notice

ABSOLUTE MAXIMUM RATINGS

Parameter Rating Unit

VIN voltage 6 V

VOUT, SW, LEDS, VHVB voltage 40 V

EN/SET voltage VIN + 0.7V V

Storage Temperature Range -65 to +160 °C

Junction Temperature Range -40 to +125 °C

8-pin TDFN package Thermal Resistance 65 °C/W

Soldering Temperature 300 °C

RECOMMENDED OPERATING CONDITIONS

Parameter Rating Unit

VIN 2.7 to 5.5 V

Ambient Temperature Range -40 to +85 °C

Typical application circuit with external components is shown on page 1.

ELECTRICAL OPERATING CHARACTERISTICS

(Over recommended operating conditions unless specified otherwise) VIN = 3.6V,TAMB = 25°C, CIN = 1µF, COUT = 1µF, L = 22 µH

Name Conditions Min Typ Max Units

VIN = 3.6 V, VOUT open 1

Quiescent Current VIN = 3.6 V, ILED = 25

mA @ VOUT =36 V 3mA

Shutdown Current VIN = 5.5V, EN = 0V 1 µA

LED Current Accuracy At factory preset value ±1 %

Oscillator Frequency 0.7 MHz

Maximum Duty Cycle 92 %

NMOSFET Switch On Resistance 0.3 Ω

PMOSFET Switch On Resistance 1.5 Ω

Switch Leakage Current 0.1 µA

Switch Current Limit 1.3 A

Dropout/Current sense voltage At factory preset value 250 mV

PWM Frequency 0.1 10 kHz

Input Resistance (pull down) 250 kΩ

High 1.4

EN/PWM

Pin Logic Level Low 0.4 V

Thermal Shutdown 150

Thermal Hysteresis 20 °C

Over-Voltage Protection 36 V

Soft Start Time 1.5 ms

Delay Time to Shutdown EN = 0 10 ms

LDS8710

Characteristics subject to change without notice

PIN DESCRIPTION

Pin # Name Function

1 VIN Input Voltage, connect to battery or power supply

2 GND Analog Ground

3 PGND Power Ground

4 SW Switch input; Connect inductor terminal to this pin

5 VOUT Output voltage; Connect to the LED string anode

terminal to this pin.

6 HVB High Voltage Bypass; Connect a 470 pF capacitor

between this point and VOUT

7 LEDS Current Sense input. Connect LED string cathode

terminal to this pin

8 EN/PWM Device Enable (active high) and Dimming Control

PAD PAD Connect to GND on the PCB

Top view: TDFN 8-lead 2 X 3 mm

PIN FUNCTION

VIN is the supply pin for the driver. A small 1 μF

ceramic bypass capacitor is required between the VIN

pin and ground near the device. The operating input

voltage range is from 2.7 V to 5.5 V. If the input

supply voltage falls below the under-voltage

threshold, switch is disabled, and the device enters

shutdown mode.

HVB is the internal high voltage reference point.

Connect a 4700 pF capacitor between this point and

VOUT.

EN/PWM is the enable and PWM control logic input.

Guaranteed levels of logic high and logic low are set

at 1.4V and 0.4V respectively. When EN/PWM is

initially taken high, the device becomes enabled and

LED current sets to maximum programmed value..

To place the device into shutdown mode, the

EN/PWM pin must be held low for more than 10 ms.

VOUT is the driver’ output that is connected to the LED

anode. A ceramic bypass capacitor of 1 µF requires

between the VOUT pin and ground near the device.

GND is the ground reference for the analog circuits.

The pin must be connected to the ground plane on

the PCB.Avoid high currents flowing trough traces

connecting this pin with EN/PWM signal source.

PGND is the current return for high current circuits.

The pin must be connected to the ground plane on

the PCB. Connect GND and PGND as close to the

driver as possible.

LEDS is the Current Sense pin that provides internal

regulated current sink for LED string. Connect LED

string cathode to this pin. This pin enter high-

impedance zero current state whenever the device is

in shutdown mode.

PAD is the exposed pad underneath the package.

For best thermal performance, the pad should be

soldered to the PCB and connected to the ground

plane

LDS8710

Characteristics subject to change without notice

TYPICAL CHARACTERISTICS

Vin = 3.6V, IOUT = 30mA (10 LEDs per string), CIN = 1 μF, COUT = 1μF, L = 22 µH, TAMB = 25°C unless otherwise specified

Power Efficiency vs. Input Voltage LED Current vs. Input Voltage

LED Current Error vs. PWM Duty Cycle LED Current Error vs. PWM Frequency

Soft Start Waveforms

Ch 1 (yellow) – EN pin, Ch 2 (green)– SW node voltage

Ch 3 (red) – Inductor current, Ch 4 (blue) - VOUT

Operating Waveforms

Ch 1 (yellow) - SW node voltage,

Ch 3 (red) – Inductor current

LDS8710

Characteristics subject to change without notice

TYPICAL CHARACTERISTICS

Vin = 3.6V, IOUT = 30mA (10 LEDsper string), CIN = 1 μF, COUT = 1μF, L = 22 µH, TAMB = 25°C unless otherwise specified

Waveforms at PWM LED Current Regulation

Ch 1 (yellow) – PWM signal at 1 kHz 5% duty cycle

C2 (green) – SW node voltage, Ch 3(red) – LED Current.

Ch4 (blue) - VOUT

Waveforms at PWM LED Current Regulation

Ch 1 (yellow) – PWM signal at 1 kHz 98% duty cycle

C2 (green) – SW node voltage, Ch 3(red) – LED Current.

Ch4 (blue) - VOUT

Waveforms at PWM LED Current Regulation

Ch 1 (yellow) – PWM signal at 30 kHz 25% duty cycle

C2 (green) – SW node voltage, Ch 3(red) – LED Current.

Ch4 (blue) - VOUT

Waveforms at PWM LED Current Regulation

Ch 1 (yellow) – PWM signal at 30 kHz 98% duty cycle

C2 (green) – SW node voltage, Ch 3(red) – LED Current.

Ch4 (blue) - VOUT

LDS8710

Characteristics subject to change without notice

BLOCK DIAGRAM

Figure 2. LDS8710 Functional Block Diagram

BASIC OPERATION

At power-up, EN/PWM pin should be logic LOW. The

LDS8710 starts operating when EN/PWM pin is

asserted logic high. If the input voltage is sufficient to

regulate all LED currents, the device remains in

operating mode. The low dropout Current regulator

performs well at VOUT voltage up to 250 mV above

summary LED forward voltage significantly increasing

driver’s efficiency.

If the input voltage is insufficient or falls to a level

where the regulated currents cannot be maintained,

the Under-Voltage protection turns device off setting

it in shutdown mode.

The LDS8710 has soft start function that prevent high

input current spike at device’ wake-up.

The EN/PWM pin should be held low for more than

10 ms to completely turn device in low current

shutdown mode.

LED Current Setting

The maximum current value in the LED string is

factory preset at 20, 25, or 30 mA. The average LED

string current that determines LED brightness may be

controlled applying PWM signal to the EN/PWM pin.

The maximum PWM frequency is 30 kHz, while

frequiencies below 100 Hz are not recommended to

avoid visible LED flikering. Duty cycle that determines

average LED string current may vary in the range

from 5% to 100% at 1 kHz or from 20% to 100% at

30 kHz with high linearity current regulation.

Protection Mode

The output voltage VOUT is limited at about 36 V. This

is to prevent the output pin from exceeding its

absolute maximum rating if LED string is

disconnected or any LED.in string burns out creating

open circuitry.

If the die temperature exceeds +150°C, the driver will

enter a thermal protection shutdown mode. When the

device temperature drops by about 20°C, the device

will resume normal operation.

If the input supply voltage falls below the under-

voltage threshold, switch is disabled, and the device

enters shutdown mode.

LED Selection

The number of the LEDs in string is limited by

maximum output voltage that cannot exceed over-

voltage protection level. We recommend using not

more than 10 LEDs with VF≤3.6 V in string if VIN

voltage is above 3.0 V and not more that six LEDs if

VIN may fall up to 2.7 V.

LDS8710

Characteristics subject to change without notice

External Components Selection

The LDS8710 requires four external components

only. The recommended input capacitor value is

between 1.0 and 10 µF, while the output cap

selection is function of desired output ripple, loop

stability, and inrush current. We recommend COUT =

1 µF.

The inductor should allow around 20% higher peak

current than LDS8710 Switch Current Limit ILIM (see

table Electrical Operating Characteristics on page 2).

However, the maximum ripple current through

inductor IRshould not exceed















 





dFLED

LIMR V

VNVI

II 2, where

VF- is a LED forward voltage, V

N – is number of LEDs per string

Vd - is a current regulator voltage drop = 0.25 V,

VIN - is an input voltage, V

We recommend continuous conduction mode for

inductor to achieve highest efficiency. That limits IR

value as





dFLED

RVVNVI







Inductor value L is a function of switching frequency,

input and output voltage and is determined by

following equation:

















ININPMdF

RVVVVNV

L11

1, where

VPM - is a voltage drop across synchronous rectifier

(PMOSFET) = 1.5 ohms x ILED, (A),

L - is an inductance, H, and

f - is a switching frequency, 700 kHz.

Inductor should have minimum DC resistance to

avoid driver’s efficiency degradation.

The equation for the output capacitor selection is:

fVVNV

IVVNV

RdF

OUTINdF

OUT )(

)(





, where

VR– is a ripple voltage at the output.

For example:

If VIN = 2.7 V, N = 10, VF= 3.6 V, Vd = 0.25 V, f =

0.7 MHz, IOUT = 30 mA, and ripple voltage VR= 0.05

V, COUT = 0.77 µF so 1 µF is a good choice.

We recommend COUT = 1 µF to achieve better

efficiency and driver’s stability.

Recommended Layout

In active mode, the driver switches internally at a high

frequency. We recommend minimize trace length to

all external capacitors and inductor. The input and

output ceramic capacitors (X5R or X7R type) should

located as close to the device’ pins as possible to

prevent from EMI distribution

A ground plane should cover the area under the

driver IC as well as the bypass capacitors. Short

connection to ground on capacitors CIN and COUT can

be implemented with the use of multiple via. A copper

area matching the TDFN exposed pad (PAD) must

be connected to the ground plane underneath. The

use of multiple via improves the package heat

dissipation.

Figure 3. Recommended layout

LDS8710

Characteristics subject to change without notice

PACKAGE DRAWING AND DIMENSIONS

8-PIN TDFN, 2mm x 3mm, 0.5mm PITCH

SYMBOL MIN NOM MAX

A 0.700 0.750 0.800

A1 - 0.000 0.050

A2 0.203 Ref.

b 0.180 0.230 0.280

D 2.950 3.000 3.050

D1 1.750 1.800 1.850

E 1.950 2.000 2.050

E1 1.550 1.600 1.650

e 0.500 Bsc

L 0.350 0.400 0.450

Note:

1. All dimensions are in millimeters

2. Complies with JEDEC Standard MO-220

LDS8710

Characteristics subject to change without notice

ORDERING INFORMATION

Part Number Package Package Marking

LDS8710 008-T21) – 300 2) TDFN - 8 2 x 3mm 3) 710

LDS8710 008-T21) – 250 2) TDFN - 8 2 x 3mm 3) 710

LDS8710 008-T21) – 200 2) TDFN - 8 2 x 3mm 3) 710

Notes:

1. Quantity per reel is 2000

2. Maximum LED current is factory preset at 20, 25, or 30 mA. Consult factory if other current values are required.

3. Matte-Tin Plated Finish (RoHS-compliant)

EXAMPLE OF ORDERING INFORMATION

Notes:

1) All packages are RoHS-compliant (Lead-free, Halogen-free).

2) The standard lead finish is Matte-Tin.

3) The device used in the above example is a LDS8710 XXX–T2-300 (2x3 TDFN, Tape & Reel, 30 mA LED Current).

4) For additional package and current options, please contact your nearest IXYS Corp. Sales office.

Optional

Company ID Package

008: 2 x 3 TDFN

Prefix Device # Suffix

LDS

8710

008

300

Product Number Tape & Reel

T: Tape & Reel

2: 2000/Reel

LED Current

300 – 30 mA

250 – 25 mA

200 – 20 mA

LDS8710

Characteristics subject to change without notice

IXYS Corp.

1590 Buckeye Dr.,

Milpitas, CA 95035-7418

Phone: 408.457.9000 Document No: 8710DS

Fax: 408.496.0222 Revision: N1.0

http://www.ixys.com Issue date: 2/8/2011

Warranty and Use

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PARTICULAR PURPOSE, NOR THAT THE USE OF ITS PRODUCTS WILL NOT INFRINGE ITS INTELLECTUAL PROPERTY RIGHTS OR THE RIGHTS OF THIRD

PARTIES WITH RESPECT TO ANY PARTICULAR USE OR APPLICATION AND SPECIFICALLY DISCLAIMS ANY AND ALL LIABILITY ARISING OUT OF ANY SUCH

USE OR APPLICATION, INCLUDING BUT NOT LIMITED TO, CONSEQUENTIAL OR INCIDENTAL DAMAGES.

IXYS Corp. products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended

to support or sustain life, or for any other application in which the failure of the IXYS Corp. product could create a situation where personal injury or death may occur.

IXYS Corp. reserves the right to make changes to or discontinue any product or service described herein without notice. Products with data sheets labeled "Advance

Information" or "Preliminary" and other products described herein may not be in production or offered for sale.

IXYS Corp. advises customers to obtain the current version of the relevant product information before placing orders. Circuit diagrams illustrate typical semiconductor

applications and may not be complete.