National Semiconductor LM2756 Technical data

December 5, 2007

LM2756 Multi-Display Inductorless LED Driver with 32 Exponential Dimming Steps in micro SMD

General Description

The LM2756 is a highly integrated, switched-capacitor, multidisplay LED driver that can drive up to 8 LEDs in parallel with a total output current of 180mA. Regulated internal current sources deliver excellent current and brightness matching in all LEDs.

The LED driver current sinks are split into three independently controlled groups. The primary group (Group A) can be configured to drive four, five or six LEDs for use in the main phone display, while the secondary group (Group B) can be configured to drive one, two or three LEDs for driving secondary displays, keypads and/or indicator LEDs. An additional driver, D1C, is provided for additional indicator lighting functions.

The device provides excellent efficiency without the use of an inductor by operating the charge pump in a gain of 3/2 or in Pass-Mode. The proper gain for maintaining current regulation is chosen, based on LED forward voltage, so that efficiency is maximized over the input voltage range.

The LM2756 is available in National’s tiny 20-bump, 0.4mm pitch, thin micro SMD package.

Features

Drives up to 8 LEDs with up to 30mA of Diode Current

■

Each 32 Exponential Dimming Steps with 800:1 Dimming Ratio

■

for Group A (Up to 6 LEDs) 8 Linear Dimming States for Groups B (Up to 3 LEDs) and

■

D1C (1 LED) Programmable Auto-Dimming Function

■

3 Independently Controlled LED Groups Via I2C

■

Compatible Interface Up to 90% Efficiency

■

Total Solution Size < 21mm

■

Low Profile 20 Bump micro SMD Package

■

(1.615mm × 2.015mm × 0.6mm)

0.4% Accurate Current Matching

■

Internal Soft-Start Limits Inrush Current

■

True Shutdown Isolation for LED’s

■

Wide Input Voltage Range (2.7V to 5.5V)

■

Active High Hardware Enable

■

Applications

Dual Display LCD Backlighting for Portable Applications

■

Large Format LCD Backlighting

■

Display Backlighting with Indicator Light

■

Typical Application Circuit

30009701

LM2756

Minimum Layout

30009741

Connection Diagram

20 Bump micro SMD Package

NS Package Number TMD20AAA

30009702

Pin Descriptions

Bump #s

TMD20AAA

A3 V

A2 V

A1, C1, B1, B2 C1+, C1-, C2+, C2- Flying Capacitor Connections

D3, E3,E4, D4 D1A-D4A LED Drivers - GroupA

C4, B4 D53, D62 LED Drivers - Configurable Current Sinks. Can be assigned to GroupA or GroupB

B3 D1B LED Drivers - GroupB

C3 D1C LED Driver - Indicator LED

D2 I

E1 HWEN Hardware Enable Pin. High = Normal Operation, Low = RESET

C2 SDIO Serial Data Input/Output Pin

E2 SCL Serial Clock Pin

A4, D1 GND Ground

Pin Names Pin Descriptions

OUT

SET

Input voltage. Input range: 2.7V to 5.5V.

Charge Pump Output Voltage

Placing a resistor (R

) between this pin and GND sets the full-scale LED current for

SET

DxA , DxB, D53, D62 and D1C LEDs. Full-Scale LED Current = 189 × (1.25V ÷ R

SET

)

Ordering Information

Order Information Package Supplied As

LM2756TM

LM2756TMX 3000 Units, Tape & Reel

www.national.com 2

TMD20AAA

250 Units, Tape & Reel

LM2756

Absolute Maximum Ratings (Notes 1, 2)

If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.

VIN pin voltage -0.3V to 6.0V

SCL, SDIO, HWEN pin voltages -0.3V to (VIN+0.3V)

w/ 6.0V max

Pin Voltages -0.3V to (V

Dxx

Continuous Power Dissipation

Internally Limited

(Note 3) Junction Temperature (T

) 150°C

J-MAX

Storage Temperature Range -65°C to +150° C Maximum Lead Temperature

(Soldering) ESD Rating(Note 5)

Human Body Model 2.0kV

+0.3V)

VOUT

w/ 6.0V max

(Note 4)

Operating Rating

(Notes 1, 2)

Input Voltage Range 2.7V to 5.5V LED Voltage Range 2.0V to 4.0V Junction Temperature (TJ) Range

Ambient Temperature (TA) Range (Note 6)

-30°C to +105°C

-30°C to +85°C

Thermal Properties

Junction-to-Ambient Thermal Resistance (θJA), TMD20 Package

40°C/W

(Note 7)

ESD Caution Notice National Semiconductor

recommends that all integrated circuits be handled with appropriate ESD precautions. Failure to observe proper ESD handling techniques can result in damage to the device.

Electrical Characteristics (Notes 2, 8)

Limits in standard typeface are for TJ = 25°C, and limits in boldface type apply over the full operating temperature range. Unless otherwise specified: VIN = 3.6V; V Current; ENA, ENB, ENC Bits = “1”; SD53, SD62, 53A, 62A Bits = "0"; C1 = C2 = CIN= C output current(s) and current setting pins (I

Symbol Parameter Condition Min Typ Max Units

Output Current Regulation GroupA

Output Current Regulation GroupB

Dxx

Output Current Regulation IDC

Maximum Diode Current per Dxx Output(Note 10)

Output Current Regulation GroupA, GroupB, and GroupC Enabled (Note 10)

Dxx-

MATCH

DxTH

LED Current Matching(Note 11)

1x to 3/2x Gain Transition

Dxx

Threshold

Current sink Headroom Voltage

Requirement (Note 12)

OUT

Open-Loop Charge Pump Output Resistance

Quiescent Supply Current Gain = 1.5x, No Load 2.1 2.5 mA

HWEN

= VIN; V

Dxx

= V

DxA

and I

DxB

) apply to GroupA and GroupB. (Note 9)

SET

= 0.4V; R

DxC

2.7V ≤ VIN ≤ 5.5V ENA = '1', 53A = 62A = '0'', ENB = ENC = '0' 4 LEDs in GroupA

2.7V ≤ VIN ≤ 5.5V ENA = '1', 53A = 62A = '1', ENB = ENC = '0' 6 LEDs in GroupA

2.7V ≤ VIN ≤ 5.5V ENB = '1', 53A = 62A = '0', ENA = ENC = '0' 3 LEDs in GroupB

2.7V ≤ VIN ≤ 5.5V ENC = '1', ENA = ENB = '0'

= 8.33kΩ

SET

3.2V ≤ VIN ≤ 5.5V V

= 3.6V

LED

= 10.5kΩ

SET

= 11.8kΩ; GroupA = GroupB = GroupC = Fullscale

SET

= 1.0µF; Specifications related to

OUT

18.65 (-8%)

18.70

(-8.5%)

18.40 (-8%)

18.20

(-7.5%)

20.28

20.40

20.00

19.70

30 mA

22.5 DxA

22.5 DxB

22.5 DxC

GroupA (4 LEDs) 0.4 1.8

2.7V ≤ VIN ≤ 5.5V

GroupB (3 LEDs) 0.7 2.5

and/or V

DxA

= 95% ×I

Dxx

(nom) ≈ 20mA)

Dxx

DxB

Dxx

Falling

(nom.)

150 mV

65 mV

Gain = 3/2 2.4

Gain = 1 0.9

21.90

(+8%)mA(%)

22.10

(+8.5%)mA(%)

21.60

(+8%)mA(%)

21.20

(+7.5%)mA(%)

%GroupA (6 LEDs) 1.0 2.7

Ω

3 www.national.com

Symbol Parameter Condition Min Typ Max Units

LM2756

SET

DxA-B-C /

SET

START

HWEN

Shutdown Supply Current All ENx bits = "0" 3.7 5.5 µA

Pin Voltage

SET

Output Current to Current Set Ratio GroupA, GroupB, GroupC

2.7V ≤ VIN ≤ 5.5V

189

1.25 V

Switching Frequency 1.0 1.3 1.6 MHz

Start-up Time

HWEN Voltage Thresholds

= 90% steady state

OUT

2.7V ≤ VIN ≤ 5.5V

250 µs

Reset 0 0.580

Normal Operation 1.075

I2C Compatible Interface Voltage Specifications (SCL, SDIO)

Input Logic Low "0"

Input Logic High "1"

Output Logic Low "0"

2.7V ≤ VIN ≤ 5.5V

= 3.5mA

LOAD

0 0.710 V

1.225

400 mV

I2C Compatible Interface Timing Specifications (SCL, SDIO)(Note 13)

SCL (Clock Period) (Note 14) 294 ns

Data In Setup Time to SCL High 100 ns

Data Out stable After SCL Low 0 ns

SDIO Low Setup Time to SCL Low (Start)

SDIO High Hold Time After SCL High (Stop)

100 ns

30009713

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics tables.

Note 2: All voltages are with respect to the potential at the GND pins.

Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 160°C (typ.) and disengages at T

= 155°C (typ.).

Note 4: For detailed soldering specifications and information, please refer to National Semiconductor Application Note 1112: Micro SMD Wafer Level Chip Scale Package (AN-1112).

Note 5: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. (MIL-STD-883 3015.7)

Note 6: In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be

derated. Maximum ambient temperature (T dissipation of the device in the application (P following equation: T

Note 7: Junction-to-ambient thermal resistance is highly dependent on application and board layout. In applications where high maximum power dissipation exists, special care must be paid to thermal dissipation issues in board design. For more information, please refer to National Semiconductor Application Note 1112: Micro SMD Wafer Level Chip Scale Package (AN-1112).

Note 8: Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm.

Note 9: CIN, C

www.national.com 4

VOUT

= T

A-MAX

, C1, and C2 : Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics

J-MAX-OP

– (θJA × P

) is dependent on the maximum operating junction temperature (T

A-MAX

), and the junction-to ambient thermal resistance of the part/package in the application (θJA), as given by the

D-MAX

= 105°C), the maximum power

J-MAX-OP

Note 10: The maximum total output current for the LM2756 should be limited to 180mA. The total output current can be split among any of the three Groups (I

= I

DxA

proper current regulation. See the Maximum Output Current section of the datasheet for more information.

= 30mA Max.). Under maximum output current conditions, special attention must be given to input voltage and LED forward voltage to ensure

DxB

DxC

Note 11: For the two groups of current sinks on a part (GroupA and GroupB), the following are determined: the maximum sink current in the group (MAX), the minimum sink current in the group (MIN), and the average sink current of the group (AVG). For each group, two matching numbers are calculated: (MAX-AVG)/ AVG and (AVG-MIN)/AVG. The largest number of the two (worst case) is considered the matching figure for the Group. The matching figure for a given part is considered to be the highest matching figure of the two Groups. The typical specification provided is the most likely norm of the matching figure for all parts.

Note 12: For each Dxx pin, headroom voltage is the voltage across the internal current sink connected to that pin. For Group A, B, and C current sinks, V V

-V

. If headroom voltage requirement is not met, LED current regulation will be compromised.

OUT

LED

HRx

Note 13: SCL and SDIO should be glitch-free in order for proper brightness control to be realized.

Note 14: SCL is tested with a 50% duty-cycle clock.

Block Diagram

LM2756

30009703

5 www.national.com

+ 11 hidden pages