SC620ULTRT - SEMTECH INTERNATIONAL

POWER MANAGEMENT

SC620

Octal LED Driver, General Purpose

Current Sink with Serial Interface

Features

Wide current setting range — 31.25μA to 25mA

Eight identical current drivers with independent

control

5% current matching, 7% accuracy

I2C interface for microprocessor control

I2C slave address 1110 000x

Less than 1μA quiescent current in shutdown

Low dropout voltage — ≤ 150mV

Over-temperature protection

MLPQ-UT-16 package (3mm x 3mm)

Ultra-thin 0.6mm maximum package height

Fully WEEE and RoHS compliant

Applications

LCD backlighting LED driver

Multicolor and RGB LED driver

General purpose current sink array

General purpose digital output (open-drain) expander

Auto-focus voice-coil driver



Description

The SC620 is a multi-purpose LED driver with eight identi-

cal, independently controlled current sinks. Each current

sink can drive an LED by connecting the LED’s anode to

the system power supply and the cathode to the current

sink input pin. Any combination of outputs can be enabled

or disabled for optimal design  exibility.

The SC620 also employs an adjustable global current gain

setting register to allow the current setting step size to

vary from 31.25μA to 500μA. This provides a wide range of

options for LED variation and dimming functions. The

maximum output is also scaled by this step size, with a

maximum of 25mA at the highest step setting.

Multi-colored and white LEDs with di erent forward volt-

ages can be driven using the same SC620 due to its  oat-

ing cathode technology. This feature allows each output

pin to vary in voltage from 150mV to VIN - 1.5V.

All current control is programmed using an I2C interface

bus. Only a single input bypass capacitor is required — no

other external resistors or capacitors are needed. The 3mm

x 3mm MLPQ package and minimal support components

make the SC620 an ideal solution for low-cost, area-con-

scious backlighting designs.

Battery

SC620

SCL

SDA

GND

ILED1

ILED2

ILED3

ILED4

ILED6

ILED7

ILED8

ILED5

Sub Panel Color/R/G/B LEDs

1μF

SCL

SDA

Main Panel

LED Backlighting

Typical Application Circuit

April 22, 2009

SC620

Pin Con guration

Marking Information

Ordering Information

Device Package

SC620ULTRT(1)(2) MLPQ-UT-16 3×3(2)

SC620EVB Evaluation Board

Notes:

(1) Available in tape and reel only. A reel contains 3,000 devices.

(2) Lead-free package only. Device is WEEE and RoHS compliant.

TOP VIEW

16 15 14 13

5678

TGND

GNDGND

GND

SCL

SDA

ILED1

ILED2

ILED3

ILED4

ILED8

ILED7

ILED6

ILED5

620

yyww

xxxx

MLPQ-UT-16; 3x3, 16 LEAD

θJA = 39°C/W

yy = two digit year of manufacture

ww = two digit week of manufacture

xxxx = lot number

SC620

Exceeding the above speci cations may result in permanent damage to the device or device malfunction. Operation outside of the parameters

speci ed in the Electrical Characteristics section is not recommended.

NOTES:

(1) Tested according to JEDEC standard JESD22-A114-B.

(2) Calculated from package in still air, mounted to 3 x 4.5 (in), 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards.

Absolute Maximum Ratings

IN (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +6.0

Pin Voltage — All Other Pins (V) . . . . . . . . . -0.3 to VIN + 0.3

ESD Protection Level(1) (kV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Recommended Operating Conditions

Ambient Temperature Range (°C) . . . . . . . . . . . . -40 to +85

Thermal Information

Thermal Resistance, Junction to Ambient(2) (°C/W) . . . .

Operating Junction Temperature (°C) . . . . . . . . -40 to +150

Storage Temperature Range (°C) . . . . . . . . . . . -65 to +150

Peak IR Re ow Temperature (10s to 30s) (°C) . . . . . . . +260

Unless otherwise noted, TA = +25°C for Typ, -40ºC to 85°C for Min and Max, VIN = 2.7V to 5.5V, CIN = 1μF, ΔVF ≤ 1.5V

Parameter Symbol Condition Min Typ Max Units

Maximum LED Current Setting(1) ILEDn 25 mA

LED Current Setting Accuracy(1) ΔILEDn

ILEDn = 15mA, VF = 3.4V,

VILEDn = 2V, TA = 25ºC -7 +7 %

Load Regulation ΔILEDn/ ΔVF

5mA < ILEDn ≤ 25mA,

TA = 25ºC -2 2 % / V

LED Current Matching Accuracy(1) ILED-to-LED ILEDn = 15mA, TA = 25ºC -5 +5 %

Dropout Voltage VDO ILEDn = 25mA 150 mV

Shutdown Current ISHDN EN = GND 0.1 1 μA

Current Step Size ISTEP

Normal Mode(3) 500 μA

Low-Current Mode(4) 31.25 μA

Quiescent Current IQ

Standby: EN = VIN,

LED1-8 disabled(2) 60 μA

EN = VIN, ILED1-8 = 1.968mA(4) 720 μA

EN = VIN, ILED1-8 = 25mA(3) 4.5 mA

Electrical Characteristics

SC620

Parameter Symbol Condition Min Typ Max Units

Current Sink Turn-on Time tON from 0 to 95% of target 1 ms

Current Sink Turn-o Time tOFF from 90% to 10% of set value 1 μs

EN Input High Threshold VIH VIN = 5.5V 1.6 V

EN Input Low Threshold VIL VIN = 2.7V 0.4 V

EN Input High Current IIH VIN = 5.5V 2 μA

Over Temperature Protection(5) TOTP 155 °C

I2C Interface(5)

Interface complies with slave mode I2C interface as described by Philips I2C speci cation version 2.1 dated January, 2000.

Digital Input Voltage

VB-IL 0.4 V

VB-IH 1.6 V

SDA Output Low Level IDIN (SDA) ≤ 3mA 0.4 V

Digital Input Current IB-IN -0.2 0.2 μA

Schmitt Trigger Input Hysteresis VHYS 0.1 V

Maximum Glitch Pulse Rejection tSP 50 ns

I/O Pin Capacitance CIN 10 pF

I2C Timing

Clock Frequency fSCL 400 440 kHz

SCL Low Period tLOW 1.3 μs

SCL High Period tHIGH 0.6 μs

Data Hold Time tHD_DAT 0μs

Data Setup Time tSU_DAT 100 ns

Setup Time for Repeated

START Condition tSU_STA 0.6 μs

Hold Time for Repeated

START Condition tHD_STA 0.6 μs

Setup Time for STOP Condition tSU_STO 0.6 μs

Electrical Characteristics (continued)

SC620

Electrical Characteristics (continued)

Parameter Symbol Condition Min Typ Max Units

I2C Timing (continued)

Bus-Free Time Between

STOP and START tBUF 1.3 μs

Interface Start-up Time tEN

Bus Start-up Time After EN Pin is

Pulled High 350 μs

Notes:

(1) Current step size = 500μA - See Table 1 for other step size options.

(2) Outputs are disabled but I2C bus is active

(3) Current gain register set to maximum value - see Control Register section for details.

(4) Current gain register set to minimum value - see Control Register section for details.

(5) Guaranteed by design.

SC620

Typical Characteristics

Low Current Settings with Anode = VIN

100

200

300

400

500

600

2.5 3 3.5 4 4.5 5 5.5

LED Current (μA)

Boundary of cathode = 150mV

500μA,V

= 2.80V

Anode supply = V

(V)

250μA,V

= 2.73V

125μA,V

= 2.68V

31.25μA,V

= 2.59V

Mid Current Settings with Anode = VIN

3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5

LED Current (mA)

Anode supply = V

15mA,V

= 3.27V

(

)

10mA,V

= 3.20V

5mA,V

= 3.08V

Boundary at cathode = 150mV

High Current Settings with Anode = VIN

3.25 3.5 3.75 44.254.5

4.75 5 5.25 5.5

LED Current (mA)

(V)

Boundary at cathode = 150mV

Anode supply = V

25mA,V

= 3.37V

15mA,V

= 3.27V

10mA,V

= 3.20V

Low Current Settings with Anode = 5V

100

200

300

400

500

600

3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5

VIN (V)

LED Current (μA)

Anode supply = 5V

500μA,VF = 2.79V

Boundary of cathode at VIN-1.5V

250μA,VF = 2.73V

125μA,VF = 2.68V

31.25μA,VF = 2.59V

Mid Current Settings with Anode = 5V

3 3.25 3.5 3.75 4 4.25 4.5 4.75 5 5.25 5.5

LED Current (mA)

Anode supply = 5V

15mA,V

= 3.26V

(V)

Boundary of cathode at V

-1.5V

10mA,V

= 3.19V

5mA,V

= 3.08V

High Current Settings with Anode = 5V

33.25

3.5 3.75 44.25 4.5 4.75 5 5.25 5.5

LED Current (mA)

VIN (V)

Anode supply = 5V

10mA,VF = 3.19V

15mA,VF = 3.26V

25mA,VF = 3.35V

Boundary of cathode at VIN-1.5V

SC620

Typical LED Current Matching

-3.5

-2.5

-1.5

-0.5

0.5

1.5

2.5

3.5

0.5 5.5 10.5 15.5 20.5 25.5

LED Current (mA)

% Matching

Gain Register Value = 0Ch

-40°C

25°C

85°C

Typical LED Current Accuracy (25°C)

-8

-6

-4

-2

0.5 5.5 10.5 15.5 20.5 25.5

% Accuracy

LED Current (mA)

All 8 LEDs fall between Max and Min, Gain Register Value = 0Ch

Max

Min

Typical LED Current Accuracy (85°C)

-8

-6

-4

-2

0.5 5.5 10.5 15.5 20.5 25.5

% Accuracy

LED Current (mA)

All 8 LEDs fall between Max and Min, Gain Register Value = 0Ch

Max

Min

Typical LED Current Accuracy (-40°C)

-8

-6

-4

-2

0.5 5.5 10.5 15.5 20.5 25.5

LED Current (mA)

% Accuracy

All 8 LEDs fall between Max and Min, Gain Register Value = 0Ch

Max

Min

SC620

Pin Descriptions

Pin # Pin Name Pin Function

1 GND Ground

2 IN Input voltage supply

3 EN Enable input — active high

4 GND Ground

5 ILED1 Current sink input for LED 1

6 ILED2 Current sink input for LED 2

7 ILED3 Current sink input for LED 3

8 ILED4 Current sink input for LED 4

9 GND Ground

10 SDA I2C serial data pin (bi-directional)

11 SCL I2C clock input

12 GND Ground

13 ILED5 Current sink input for LED 5

14 ILED6 Current sink input for LED 6

15 ILED7 Current sink input for LED 7

16 ILED8 Current sink input for LED 8

T Thermal Pad Thermal pad for heatsinking purposes. Connect to ground plane using multiple vias. Not connected

internally.

SC620

Block Diagram

GND

ILED1

DAC

Digital

Interface

and

Control

Registers

Voltage

Reference

DAC

SDA

SCL

ILED2

ILED3

ILED4

ILED5

ILED6

ILED7

ILED8

GND GND GND

SC620

General Description

The SC620 includes eight independently controlled

current sinks designed to control LED backlighting for

mobile phones and other battery-operated handheld

devices. As LED forward voltages decrease for white, blue,

and other colored LEDs, there is less need for voltage

boosting devices for powering backlight and indicator

LEDs. In these types of systems where there is a fixed

supply voltage large enough to supply the LEDs or where

the LEDs can be powered over the entire battery range,

the SC620 provides a simple low-cost driver alternative to

charge pump or inductor-based switching boost

converters.

Current Sink Design

Each current sink is designed for a pin voltage range

between 150mV and VIN - 1.5V. This feature allows the

system to operate backlight LEDs with constant current

without interference caused by blinking indicator LEDs or

driving LEDs with various forward voltages and currents.

Protection Circuitry

The SC620 contains protection circuitry that prevents

damage from operating in an unspecified state. These

features include:

Under-voltage Lockout Protection

Over-temperature Protection

Short-circuit Protection

Under-Voltage Lockout

An Under-Voltage Lockout Protection (UVLO) circuit dis-

ables the device in the event that the input voltage falls

below the threshold. UVLO typically occurs at 2V.

Hysteresis is provided to prevent chatter.

Short-Circuit Protection

The output sink pins ILED1 through ILED8 are protected

against shorting to VIN, prevent device damage in the

event of a shorted LED. The source lead of each sink is con-

nected to ground, so the output sink pins do not require

protection against being externally shorted to ground, as

this would result in zero potential across the sink device.

Over-Temperature Protection

The Over-temperature Protection circuit helps prevent the

device from overheating and experiencing a catastrophic

•

failure. When the junction temperature exceeds 155°C,

the device is disabled and remains disabled until the

junction temperature is reduced.

Layout Considerations

The MLPQ-UT-16 package has a thermal die attach pad

located at the center. This pad must be connected to the

ground plane through multiple vias as shown (illustration

not to scale).

SCL

SC620

GND

ILED1

ILED2

ILED3

ILED4 ILED5

ILED6

ILED7

ILED8

SDA

GND GND

GND

Ground plane

For low noise, four ground pins are located at the corner

pins 1, 4, 9 and 12. Connect each of the ground pins

directly to the ground plane as shown.

The layout is simple and requires very few components in

addition to the LEDs that it will drive. A 1μF decoupling

capacitor at the IN pin is required. Place this capacitor

near pin 2, and ground it close to the SC620 as shown.

Applications Information

SC620

Applications Information (continued)

Application Circuit Examples

Main Backlight Plus Sub-panel Backlight Plus Single

RGB LED

This example uses the SC620 to drive a main display, a

sub-panel display, and an RGB LED. Independent outputs

allow these functions to be supported simultaneously at

di erent intensities. The VIN supply is typically single cell

Li-Ion or 5.0V. VIN supply and LED anode voltage may

be from di erent sources. The operating voltage limit of

(VIN - 1.5V) at the sink pins must be observed to achieve

the speci ed accuracy of the device.

Battery

SC620

SCL

SDA

GND

ILED1

ILED2

ILED3

ILED4

ILED6

ILED7

ILED8

ILED5

Sub Panel Color/R/G/B LEDs

1μF

SCL

SDA

Main Panel

LED Backlighting

10 7

SC620

Backlighting Three LEDs of Any Color Combination

Plus Lens Voice Coil Drive and One GPO

This example uses the SC620 to drive 3 backlight LEDs,

plus a voice coil actuator for lens auto-focus and one

open-drain digital output. Independent outputs allow

these functions to be supported simultaneously. The VIN

supply is typically single cell Li-Ion or 5.0V. VIN and the

LED anode voltage may be supplied by di erent sources.

The operating voltage limit of (VIN - 1.5V) at the sink pins

must be observed to achieve the speci ed accuracy of the

device.

SC620

SCL

SDA

GND

ILED1 5

ILED2 6

ILED3 7

ILED4 8

ILED6 14

ILED8 16

ILED5 13

LOGIC

1μF

SCL

SDA

Main Panel

LED Backlighting Lens Focusing

BAT

= 2.7V to 5.5V

BAT

Voice

Coil

ILED7 15

GPO

Digital Output Expander

Applications Information (continued)

SC620

Applications Information (continued)

Backlighting with Series Connected LEDs connected

to a Boosted Output Voltage

This example uses the SC620 to drive 32 LEDs in a 4-in-

series by 8-in-parallel arrangement. Other arrangements

of series and parallel combinations are possible.

To prevent the boost voltage from illuminating the LEDs

while the current sinks are off, the boost voltage must

follow the SC620 in the start-up sequence. The boost

voltage must also power-o before the current sinks turn

o in the shut-down sequence. Protection diodes may be

necessary to protect the current sinks from destructive

voltage levels produced by the boost voltage supply.

Schottky diodes are shown in the schematic for the

purpose of voltage clamping. These diodes prevent

damage to the current sinks in the event that the sink

turns o while the boost circuit is on.

The operating voltage limit of (VIN - 1.5V) at the sink pins

must be observed to achieve the speci ed accuracy of the

device.

SC620

SCL

SDA

GND

ILED1 5

ILED2 6

ILED3 7

ILED4 8

ILED6 14

ILED715

ILED8 16

ILED5 13

1μF

SCL

SDA

LED Backlighting

= (3/7)*(R

)

Limit SC620 sink pins to < [VIN – 1.5]

DC/DC Boost Voltage

Boost

limiting

SC620

SC620 Slave Address

Following a start condition, the bus master outputs the

address of the slave device. The 7 bit slave address for the

SC620 is 1110 000x. The eighth bit is the data direction bit

and also the least signi cant bit (LSB). E0h is used for a

write operation, and E1h is used for a read operation.

DEVICE ADDRESS R/W

11100001/0

Dimming Control Register Description

The dimming control registers set the multiplier used to

determine the absolute current setting. Current setting for

each current sink is determined by multiplying the current

step size (as described in Table 1) by the decimal multiplier

in each dimming control register. For example, if the

current step size is set to 500μA and the L1 Dimming

Control Register bits (L1_5 through L1_0) are set to 010100

(20 decimal), then the output current for ILED1 is set to 20

x 500μA = 10mA. Note that the maximum current setting

occurs when the dimming control register bits are set to

110010 (50 decimal) - any bit combination larger than this

one will default to the maximum setting.

Address D7 D6 D5 D4 D3 D2 D1 D0 Description Default (1)

00h

L8_EN

1 = on

0 = o

L7_EN

1 = on

0 = o

L6_EN

1 = on

0 = o

L5_EN

1 = on

0 = o

L4_EN

1 = on

0 = o

L3_EN

1 = on

0 = o

L2_EN

1 = on

0 = o

L1_EN

1 = on

0 = o

LED on/o control 00h

01h X X L1_5 L1_4 L1_3 L1_2 L1_1 L1_0 LED1 dimming control 01h

02h XX

L2_5 L2_4 L2_3 L2_2 L2_1 L2_0 LED2 dimming control 01h

03h XX

L3_5 L3_4 L3_3 L3_2 L3_1 L3_0 LED3 dimming control 01h

04h XX

L4_5 L4_4 L4_3 L4_2 L4_1 L4_0 LED4 dimming control 01h

05h XX

L5_5 L5_4 L5_3 L5_2 L5_1 L5_0 LED5 dimming control 01h

06h XX

L6_5 L6_4 L6_3 L6_2 L6_1 L6_0 LED6 dimming control 01h

07h XX

L7_5 L7_4 L7_3 L7_2 L7_1 L7_0 LED7 dimming control 01h

08h XX

L8_5 L8_4 L8_3 L8_2 L8_1 L8_0 LED8 dimming control 01h

09h XXX X G4 G3 G2 G1 gain register 08h

Note

(1) Default value is the register contents immediately following a high transition at the enable pin.

Table 1 - Gain Setting Values (default = 1000)

G4 G3 G2 G1 Current Step

Size (μA)

0000 31.25

0001 62.5

0010 93.75

0011 125

0100 156.25

0101 187.5

0110 218.75

0111 250

1000 281.25

1001 312.5

1010 343.75

1011 375

1100 406.25

1101 437.5

1110 468.75

1111 500

SC620

Using the I2C Serial Port

The I2C General Speci cation

The SC620 is a read-write slave-mode I2C device and com-

plies with the Philips I2C standard Version 2.1 dated

January, 2000. The SC620 has eight user-accessible inter-

nal 8-bit registers. While there is no auto increment/decre-

ment capability in the SC620 I2C logic, a tight software

loop can be designed to randomly access the next register

independent of which register you begin accessing. The

start and stop commands frame the data-packet and the

repeat start condition is allowed if necessary.

SC620 Limitations to the I2C Speci cations

Seven bit addressing is used and ten bit addressing is not

allowed. Any general call address will be ignored by the

SC620. The SC620 is not CBUS compatible. The SC620 can

operate in standard mode (100kbit/s) or fast mode

(400kbit/s).

Supported Formats:

Direct Format — Write

The simplest format for an I2C write is Direct Format. After

the start condition [S], the slave address is sent, followed

by an eighth bit indicating a write. The SC620 I2C then

acknowledges that it is being addressed, and the master

responds with an 8 bit data byte consisting of the register

address. The slave acknowledges and the master sends

the appropriate 8 bit data byte. Once again the slave

acknowledges and the master terminates the transfer with

the stop condition [P].

Combined Format — Read

After the start condition [S], the slave address is sent, fol-

lowed by an eighth bit indicating a write. The SC620 I2C

then acknowledges that it is being addressed, and the

master responds with an 8 bit data byte consisting of the

sends the repeated start condition [Sr]. Once again, the

slave address is sent, followed by an eighth bit indicating

a read. The slave responds with an acknowledge and the

previously addressed 8 bit data byte; the master then sends

a non-acknowledge (NACK). Finally, the master terminates

the transfer with the stop condition [P].

Stop Separated Reads

Stop separated reads can also be used. This format allows

a master to set up the register address pointer for a read

and return to that slave at a later time to read the data. In

this format the slave address followed by a write command

are sent after a start [S] condition. The SC620 then acknowl-

edges it is being addressed, and the master responds with

the 8-bit register address. The master sends a stop or restart

condition and may then address another slave. After per-

forming other tasks, the master can send a start or restart

condition to the device with a read command. The SC620

acknowledges this request and returns the data from the

SC620

Using the I2C Serial Port (continued)

I2C Direct Format Write

Slave Address Register Address DataSWA A AP

S – Start Condition

W – Write = ‘0’

A – Acknowledge (sent by slave)

P – Stop condition

Slave Address – 7-bit

Data – 8-bit

I2C Stop Separated Format Read

Slave Address Register Address Slave Address B Data NACKSWA A S/Sr RA PPSlave Address

Master Addresses