LM27964 [TI]

LM27964 White LED Driver System with I2C Compatible Brightness Control;


型号：	LM27964
厂家：	TEXAS INSTRUMENTS
描述：	LM27964 White LED Driver System with I2C Compatible Brightness Control
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中文：	中文翻译
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LM27964

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SNOSAL6D –MAY 2005–REVISED MAY 2013

LM27964 White LED Driver System with I2C Compatible Brightness Control

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FEATURES

APPLICATIONS

•

87% Peak LED Drive Efficiency

•

Mobile Phone Display Lighting

Mobile Phone Keypad Lighting

PDAs Backlighting

0.2% Current Matching between Current Sinks

Drives 6 LEDs with up to 30mA per LED in

Two Distinct Groups, for Backlighting Two

Displays (main LCD and sub LCD)

General LED Lighting

•

Dedicated Keypad LED Driver with up to 80mA

of Drive Current

DESCRIPTION

The LM27964 is a charge-pump-based white-LED

driver that is ideal for mobile phone display

backlighting. The LM27964 can drive up to 6 LEDs in

parallel along with multiple keypad LEDs, with a total

output current up to 180mA. Regulated internal

current sources deliver excellent current matching in

all LEDs.

Independent Resistor-Programmable Current

Settings

I²C Compatible Brightness Control Interface

•

Adaptive 1×- 3/2× Charge Pump

Extended Li-Ion Input: 2.7V to 5.5V

Small Low Profile Industry Standard Leadless

Package, WQFN-24 : (4mm x 4mm x 0.8mm)

The LED driver current sources are split into two

independently controlled groups. The primary group

(4 LEDs) can be used to backlight the main phone

display and the second group (2 LEDs) can be used

to backlight a secondary display. A single Keypad

LED driver can power up to 16 keypad LEDs with a

current of 5mA each. The LM27964 has an I²C

compatible interface that allows the user to

independently control the brightness on each bank of

LEDs.

•

LM27964SQ-I LED PWM Frequency = 10kHz,

LM27964SQ-C LED PWM frequency = 23kHz

Typical Application Circuit

MAIN DISPLAY

SUB DISPLAY

KEYPAD LEDs

OUT

DKEY

D1A D2A D3A D4A

D1B D2B

OUT

LM27964

SETA

SETB

SETK

GND

SCL

SDIO

VIO

SETB

SETK

SETA

I C Compatible

Interface

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

All trademarks are the property of their respective owners.

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

LM27964

SNOSAL6D –MAY 2005–REVISED MAY 2013

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DESCRIPTION (CONTINUED)

The LM27964 works off an extended Li-Ion input voltage range (2.7V to 5.5V). 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 LM27964 is available in TI's small 24-pin WQFN Package (WQFN-24).

Connection Diagram

DAP

18 17 16 15 14 13

Bottom View

13 14 15 16 17 18

Top View

Figure 1. 24 Pin Quad WQFN Package

See Package Number RTW0024A

Table 1. Pin Descriptions

Pin #s

Pin Names

Pin Descriptions

V_IN

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

Charge Pump Output Voltage

P_OUT

19, 22 (C1)

20, 21 (C2)

C1, C2

Flying Capacitor Connections

13, 14, 15, 16

D4A, D3A, D2A, D1A LED Drivers - GroupA

4, 5

D1B, D2B

DKEY

LED Drivers - GroupB

LED Driver - KEYPAD

I_SETA

Placing a resistor (R_SETA) between this pin and GND sets the full-scale LED current for Group

A LEDs. LED Current = 200 × (1.25V ÷ R_SETA

)

I_SETB

I_SETK

Placing a resistor (R_SETB) between this pin and GND sets the full-scale LED current for Group

B LEDs. LED Current = 200 × (1.25V ÷ R_SETB

)

Placing a resistor (R_SETK) between this pin and GND sets the total LED current for the

KEYPAD LEDs. Keypad LED Current = 800 × (1.25V ÷ R_SETK

)

SCL

SDIO

VIO

Serial Clock Pin

Serial Data Input/Output Pin

Serial Bus Voltage Level Pin

Ground

9, 10, 18, DAP

8, 11

GND

No Connect

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Absolute Maximum Ratings^(1)(2)(3)

V_INpin voltage

-0.3V to 6.0V

SCL, SDIO, VIO pin voltages

-0.3V to (V_IN+0.3V)w/ 6.0V max

I_DxxPin Voltages

-0.3V to (V_POUT+0.3V)w/ 6.0V max

Continuous Power Dissipation⁽⁴⁾

Internally Limited

150ºC

Junction Temperature (T_J-MAX

Storage Temperature Range

)

-65ºC to +150º C

See⁽⁵⁾

Maximum Lead Temperature (Soldering)

ESD Rating⁽⁶⁾

Human Body Model - I_DxxPins:

1.0kV

Human Body Model - All other Pins:

2.0kV

(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 ensured. Operating Ratings do not imply ensured performance limits. For ensured performance limits

and associated test conditions, see the Electrical Characteristics tables.

(2) All voltages are with respect to the potential at the GND pin.

(3) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and

specifications.

(4) Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at T_J= 170°C (typ.) and

disengages at T_J= 165°C (typ.).

(5) For detailed soldering specifications and information, see the TI AN-1187 Application Report (SNOA401).

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

Operating Rating⁽¹⁾⁽²⁾

Input Voltage Range

2.7V to 5.5V

2.0V to 4.0V

LED Voltage Range

Junction Temperature (T_J) Range

Ambient Temperature (T_A) Range⁽³⁾

-30°C to +100°C

-30°C to +85°C

(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 ensured. Operating Ratings do not imply ensured performance limits. For ensured performance limits

and associated test conditions, see the Electrical Characteristics tables.

(2) All voltages are with respect to the potential at the GND pin.

(3) 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_A-MAX) is dependent on the maximum operating junction temperature (T_J-MAX-OP

100°C), the maximum power dissipation of the device in the application (P_D-MAX), and the junction-to ambient thermal resistance of the

part/package in the application (θ_JA), as given by the following equation: T_A-MAX= T_J-MAX-OP– (θ_JA× P_D-MAX).

Thermal Properties

Juntion-to-Ambient Thermal Resistance (θ_JA), RTW0024A Package⁽¹⁾

41.3°C/W

(1) 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, see the TI AN-1187

Application Report (SNOA401).

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Electrical Characteristics⁽¹⁾⁽²⁾

Limits in standard typeface are for T_J= 25°C, and limits in boldface type apply over the full operating temperature range.

Unless otherwise specified: V_IN= 3.6V; V_DxA= 0.4V; V_DxB= 0.4V; V_DKEY= 0.4V; R_SETA= R_SETB= R_SETK= 16.9kΩ; BankA,

BankB, and DKEY = Fullscale Current; ENA, ENB, ENK Bits = “1”; C1=C2=1.0µF, C_IN=C_OUT=2.2µF; Specifications related to

output current(s) and current setting pins (I_Dxxand I_SETx) apply to BankA, BankB and DKEY.⁽³⁾

Symbol

Parameter

Condition

Min

Typ

Max

Units

3.0V ≤ V_IN≤ 5.5V

BankA or BankB Full-Scale

ENA or ENB = "1", ENK = “0”

13.77

(-10%)

16.83

(+10%)

(%)

15.3

3.0V ≤ V_IN≤ 5.5V

BankA or BankB Half-Scale

ENA or ENB = "1", ENK = “0”

Output Current Regulation

BankA or BankB Enabled

7.5

2.7V ≤ V_IN≤ 3.0V

BankA or BankB Full-Scale

ENA or ENB = "1", ENK = “0”

I_Dxx

3.0V ≤ V_IN≤ 5.5V

DKEY Full-Scale

ENA = ENB = “0”, ENK = “1”

Output Current Regulation

Keypad Driver Enabled

52.8

(-12%)

67.2

(+12%)

(%)

3.2V ≤ V_IN≤ 5.5V

R_SETA= 8.3kΩ, R_SETK= 16.9kΩ

V_LED= 3.6V

BankA and DKEY Full-Scale

ENA = ENK = “1”, ENB = “0”

DxA

Output Current Regulation

BankA and DKEY Enabled⁽⁴⁾

DKEY

Gain = 3/2

Gain = 1

2.75

Open-Loop Charge Pump Output

Resistance

R_OUT

Ω

V_Dxx1x to 3/2x Gain Transition

Threshold

V_DxTH

V_DxAand/or V_DxBFalling

375

I_Dxx= 95% ×I_Dxx(nom.)

(I_Dxx(nom) ≈ 15mA)

BankA and/or BankB Full-Scale

Gain = 3/2, ENA and/or ENB = "1"

180

Current Source Headroom Voltage

Requirement⁽⁵⁾

V_HR

I_DKEY= 95% ×I_DKEY(nom.)

(I_DKEY(nom) ≈ 60mA)

DKEY Full-Scale

180

Gain = 3/2, ENK = "1"

I_Dxx-MATCHLED Current Matching

See⁽⁶⁾

0.2

1.3

1.7

µA

I_Q

Quiescent Supply Current

Shutdown Supply Current

I_SETPin Voltage

Gain = 1.5x, No Load

All ENx bits = "0"

2.7V ≤ V_IN≤ 5.5V

I_SD

V_SET

I_{DxA-B /}

I_SETA-B

I_DKEY

I_SETK

3.0

1.25

Output Current to Current Set Ratio

BankA and BankB

200

800

Output Current to Current Set Ratio

DKEY

f_SW

Switching Frequency

Start-up Time

500

700

250

900

kHz

µs

t_START

P_OUT= 90% steady state

(1) All voltages are with respect to the potential at the GND pin.

(2) Min and Max limits are specified by design, test, or statistical analysis. Typical numbers are not ensured, but do represent the most

likely norm.

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

(4) The maximum total output current for the LM27964 should be limited to 180mA. The total output current can be split among any of the

three banks (I_DxA= I_DxB= 30mA Max., I_DKEY= 80mA Max.). Under maximum output current conditions, special attention must be given

to input voltage and LED forward voltage to ensure proper current regulation. See the Maximum Output Current section of the datasheet

for more information.

(5) For each I_Dxxoutput pin, headroom voltage is the voltage across the internal current sink connected to that pin. For Group A and B

outputs, V_HR= V_OUT-V_Dxx. If headroom voltage requirement is not met, LED current regulation will be compromised.

(6) For the two groups of outputs on a part (BankA and BankB), the following are determined: the maximum output current in the group

(MAX), the minimum output current in the group (MIN), and the average output 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 bank. The matching figure for a given part is considered to be the highest matching figure of the two banks. The

typical specification provided is the most likely norm of the matching figure for all parts.

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Electrical Characteristics⁽¹⁾⁽²⁾

(continued)

Limits in standard typeface are for T_J= 25°C, and limits in boldface type apply over the full operating temperature range.

Unless otherwise specified: V_IN= 3.6V; V_DxA= 0.4V; V_DxB= 0.4V; V_DKEY= 0.4V; R_SETA= R_SETB= R_SETK= 16.9kΩ; BankA,

BankB, and DKEY = Fullscale Current; ENA, ENB, ENK Bits = “1”; C1=C2=1.0µF, C_IN=C_OUT=2.2µF; Specifications related to

output current(s) and current setting pins (I_Dxxand I_SETx) apply to BankA, BankB and DKEY.⁽³⁾

Symbol

Parameter

Condition

Min

Typ

Max

Units

LM27964SQ-I

LM27964SQ-C

f_PWM

Internal Diode Current PWM Frequency

kHz

D.C. Step Diode Current Duty Cycle Step

I²C Compatible Interface Voltage Specifications (SCL, SDIO, VIO)

1/16

Fullscale

V_IO

Serial Bus Voltage Level

1.8

V_IN

0.27 ×

V_IO

V_IL

Input Logic Low "0"

2.7V ≤ V_IN≤ 5.5V

0.73 ×

V_IO

V_IH

Input Logic High "1"

Output Logic Low "0"

2.7V ≤ V_IN≤ 5.5V

V_IO

V_OL

I_LOAD= 2mA

400

I²C Compatible Interface Timing Specifications (SCL, SDIO, VIO)⁽⁷⁾

t₁

t₂

t₃

SCL (Clock Period)

2.5

100

µs

Data In Setup Time to SCL High

Data Out stable After SCL Low

SDIO Low Setup Time to SCL Low

(Start)

t₄

t₅

100

SDIO High Hold Time After SCL High

(Stop)

(7) SCL and SDIO should be glitch-free in order for proper brightness control to be realized.

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Block Diagram

MAIN DISPLAY

SUB DISPLAY

KEYPAD LEDs

OUT

2.2 mF

1 mF

C1+

C1- C2+

C2-

OUT

D1B

DKEY

D1A D2A D3A D4A

D2B

2.7V to 5.5V

3/2X and 1X

Regulated Charge Pump

KEYPAD

DRIVER

MAIN DISPLAY

DRIVERS

SUB DISPLAY

DRIVERS

2.2 mF

GAIN

CONTROL

LED

SENSE

LED

SENSE

Soft-

Start

1.25V

Ref.

Brightness

Control

Brightness

Control

Brightness

Control

700 kHz

Switch

Frequency

10 kHz or

23 kHz PWM

Current Clock

General Purpose Register

SCL

SDIO

VIO

Brightness Control Register

Bank A and Bank B

I C Interface

Block

Brightness Control Register

KEYPAD

LM27964-I/C

KEY

SETA

SETB

GND

KEY

SETA

SETB

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Typical Performance Characteristics

Unless otherwise specified: V_IN= 3.6V; V_LEDxA= 3.6V, V_LEDxB= 3.6V; R_SETA= R_SETB= R_SETK= 16.9kΩ; C₁=C₂=1µF , and C_IN

C_POUT= 2.2µF.

LED Drive Efficiency

Charge Pump Output Voltage

Input Voltage

Figure 2.

Figure 3.

Shutdown Current

Input Voltage

Diode Current

Input Voltage

Figure 4.

Figure 5.

BankA/BankB Diode Current

Brightness Register Code

BankA Diode Current

BankA Headroom Voltage

Figure 6.

Figure 7.

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Typical Performance Characteristics (continued)

Unless otherwise specified: V_IN= 3.6V; V_LEDxA= 3.6V, V_LEDxB= 3.6V; R_SETA= R_SETB= R_SETK= 16.9kΩ; C₁=C₂=1µF , and C_IN

C_POUT= 2.2µF.

BankB Diode Current

BankB Headroom Voltage

Keypad Driver Current

Input Voltage

Figure 8.

Figure 9.

Keypad Driver Current

vs.

Brightness Register Code

Keypad Diode Current

Keypad Headroom Voltage

Figure 10.

Figure 11.

Keypad Driver Current

Keypad R_SETResistance

Figure 12.

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Circuit Description

OVERVIEW

The LM27964 is a white LED driver system based upon an adaptive 1.5x/1x CMOS charge pump capable of

supplying up to 180mA of total output current. With three separately controlled banks of constant current sinks,

the LM27964 is an ideal solution for platforms requiring a single white LED driver for main and sub displays, as

well as other general purpose lighting needs. The tightly matched current sinks ensure uniform brightness from

the LEDs across the entire small-format display.

Each LED is configured in a common anode configuration, with the peak drive current being programmed

through the use of external R_SETxresistors. An I²C compatible interface is used to enable and vary the brightness

within the individual current sink banks. For BankA and BankB, 16 levels of PWM brightness control are

available, while 4 analog levels are present for the DKEY driver.

CIRCUIT COMPONENTS

Charge Pump

The input to the 1.5x/1x charge pump is connected to the V_INpin, and the regulated output of the charge pump is

connected to the V_OUTpin. The recommended input voltage range of the LM27964 is 3.0V to 5.5V. The device’s

regulated charge pump has both open loop and closed loop modes of operation. When the device is in open

loop, the voltage at V_OUTis equal to the gain times the voltage at the input. When the device is in closed loop,

the voltage at V_OUTis regulated to 4.6V (typ.). The charge pump gain transitions are actively selected to maintain

regulation based on LED forward voltage and load requirements. This allows the charge pump to stay in the

most efficient gain (1x) over as much of the input voltage range as possible, reducing the power consumed from

the battery.

LED Forward Voltage Monitoring

The LM27964 has the ability to switch converter gains (1x or 3/2x) based on the forward voltage of the LED load.

This ability to switch gains maximizes efficiency for a given load. Forward voltage monitoring occurs on all diode

pins within BankA and BankB (DKEY is not monitored). At higher input voltages, the LM27964 will operate in

pass mode, allowing the POUT voltage to track the input voltage. As the input voltage drops, the voltage on the

DXX pins will also drop (V_DXX= V_POUT– V_LEDx). Once any of the active Dxx pins reaches a voltage approximately

equal to 375mV, the charge pump will then switch to the gain of 3/2. This switchover ensures that the current

through the LEDs never becomes pinched off due to a lack of headroom on the current sources.

Only active Dxx pins will be monitored. For example, if only BankA is enabled, the LEDs in BankB will not affect

the gain transition point. If both banks are enabled, all diodes will be monitored, and the gain transition will be

based upon the diode with the highest forward voltage. The DKEY pin is not monitored as it is intended to be for

keypad LEDs. Keypad LEDs generally require lower current, resulting in lower forward voltage compared to the

BankA and BankB LEDs that have higher currents. In the event that only the DKEY driver is enabled without

either BankA or BankB, the charge pump will default to 3/2 mode to ensure the DKEY driver has enough

headroom.

It is not recommended that any of the BankA or BankB drivers be left disconnected if either bank will be used in

the application. If Dxx pin/s are left unconnected, the LM27964 will default to the gain of 3/2. If the BankA or

BankB drivers are not going to be used in the application, leaving the Dxx pins is acceptable as long as the ENx

bit in the general purpose register is set to "0".

I²C Compatible Interface

DATA VALIDITY

The data on SDIO line must be stable during the HIGH period of the clock signal (SCL). In other words, state of

the data line can only be changed when CLK is LOW.

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SCL

SDIO

data

change

allowed

data

change

allowed

data

valid

data

change

allowed

data

valid

Figure 13. Data Validity Diagram

A pull-up resistor between VIO and SDIO must be greater than [(VIO-V_OL) / 2mA] to meet the V_OLrequirement

on SDIO. Using a larger pull-up resistor results in lower switching current with slower edges, while using a

smaller pull-up results in higher switching currents with faster edges.

START AND STOP CONDITIONS

START and STOP conditions classify the beginning and the end of the I²C session. A START condition is

defined as SDIO signal transitioning from HIGH to LOW while SCL line is HIGH. A STOP condition is defined as

the SDIO transitioning from LOW to HIGH while SCL is HIGH. The I²C master always generates START and

STOP conditions. The I²C bus is considered to be busy after a START condition and free after a STOP condition.

During data transmission, the I²C master can generate repeated START conditions. First START and repeated

START conditions are equivalent, function-wise. The data on SDIO line must be stable during the HIGH period of

the clock signal (SCL). In other words, the state of the data line can only be changed when CLK is LOW.

SDIO

SCL

STOP condition

TART condition

Figure 14. Start and Stop Conditions

TRANSFERING DATA

Every byte put on the SDIO line must be eight bits long, with the most significant bit (MSB) being transferred first.

Each byte of data has to be followed by an acknowledge bit. The acknowledge related clock pulse is generated

by the master. The master releases the SDIO line (HIGH) during the acknowledge clock pulse. The LM27964

pulls down the SDIO line during the 9th clock pulse, signifying an acknowledge. The LM27964 generates an

acknowledge after each byte has been received.

After the START condition, the I²C master sends a chip address. This address is seven bits long followed by an

eighth bit which is a data direction bit (R/W). The LM27964 address is 36h. For the eighth bit, a “0” indicates a

WRITE and a “1” indicates a READ. The second byte selects the register to which the data will be written. The

third byte contains data to write to the selected register.

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ack from slave

ack

ack from slave

start

msb Chip Address lsb

ack

msb Register Add lsb

msb DATA lsb

ack stop

SCL

SDIO

start

Id = 36h

ack

addr = 10h

ack

address h‘06 data

ack stop

(1) w = write (SDIO = "0", r = read (SDIO = "1"), ack = acknowledge (SDIO pulled down by either master or slave), rs =

repeated start, id = chip address, 36h for LM27964

Figure 15. Write Cycle⁽¹⁾

INTERNAL REGISTERS OF LM27964

Internal Hex Address

Power On Value

0000 0000

General Purpose Register

10h

A0h

Bank A and Bank B Birghtness Control

0000 0000

KEYPAD Brightness Control

B0h

0000 0000

MSB

LSB

bit7

bit6

bit5

bit4

bit3

ENK

bit2

ENB

bit1

ENA

bit0

Figure 16. General Purpose Register Description

Internal Hex Address: 10h

NOTE

ENA: Enables DxA LED drivers (Main Display)

ENB: Enables DxB LED drivers (Sub Display)

ENK: Enables Keypad Driver

DxA Drivers Enabled

MSB

LSB

bit7

bit6

bit5

bit4

bit3

ENK

bit2

ENB

bit1

ENA

bit0

Figure 17. General Purpose Register Example

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MSB

LSB

DxB3

bit7

DxB2

bit6

DxB1

bit5

DxB0

bit4

DxA3

bit3

DxA2

bit2

DxA1

bit1

DxA0

bit0

DxB Brightness Control

DxA Brightness Control

Figure 18. Brightness Control Register Description

Internal Hex Address: A0h

NOTE

DxA3-DxA0: Register Sets Current Level Supplied to DxA LED drivers

DxB3-DxB0: Register Sets Current Level Supplied to DxB LED drivers

Full-Scale Current set externally by the following equation:

I_Dxx= 200 × 1.25V / R_SETx

Brightness Level Segments = 1/16th of Fullscale

Full Scale Brightness

MSB

LSB

DxB3

bit7

DxB2

bit6

DxB1

bit5

DxB0

bit4

DxA3

bit3

DxA2

bit2

DxA1

bit1

DxA0

bit0

DxB Brightness Control

DxA Brightness Control

Half Scale Brightness

MSB

LSB

DxB3

bit7

DxB2

bit6

DxB1

bit5

DxB0

bit4

DxA3

bit3

DxA2

bit2

DxA1

bit1

DxA0

bit0

DxB Brightness Control

DxA Brightness Control

Figure 19. Brightness Control Register Example

DKEY Driver Enabled

Full-Scale

MSB

LSB

bit7

bit6

bit5

bit4

bit3

bit2

DKEY1

bit1

DKEY0

bit0

Figure 20. Internal Hex Address: B0h

NOTE

DKEY1-DKEY0: Sets Brightness for DKEY pin (KEYPAD Driver). 11=Fullscale

Bit7 to Bit 2: Not Used

Full-Scale Current set externally by the following equation:

I_DKEY= 800 × 1.25V / R_SETx

Brightness Level are= 100% (Fullscale), 70%, 40%, 20%

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APPLICATION INFORMATION

SETTING LED CURRENT

The current through the LEDs connected to DxA, DxB and DKEY can be set to a desired level simply by

connecting an appropriately sized resistor (R_SETx) between the I_SETxpin of the LM27964 and GND. The DxA and

DxB LED currents are proportional to the current that flows out of the I_SETAand I_SETBpins and are a factor of 200

times greater than the I_SETA/Bcurrents. The DKEY current is proportional to the current that flows out of the I_SETK

pin and is a factor of 800 times greater than the I_SETKcurrent. The feedback loops of the internal amplifiers set

the voltage of the I_SETxpins to 1.25V (typ.). Separate R_SETxresistor should be used on each I_SETxpin. The

statements above are simplified in the equations below:

I_DxA/B= 200 × (V_ISET/ R_SETA/B

R_SETA/B= 200 × (1.25V / I_DxA/B

I_DKEY= 800 × (V_ISET/ R_SETK

R_SETK= 800 × (1.25V / I_DKEY

)

Once the desired R_SETxvalues have been chosen, the LM27964 has the ability to internally dim the LEDs by

Pulse Width Modulating (PWM) the current. The PWM duty cycle is set through the I²C compatible interface.

LEDs connected to BankA and BankB current sinks (DxA and DxB) can be dimmed to 16 different levels/duty-

cycles (1/16th of full-scale to full-scale). The internal PWM frequency for BankA and BankB is a fixed 10kHz

(LM27964SQ-I) or 23kHz (LM27964SQ-C) depending on the option.

The DKEY current sink uses an analog current scaling method to control LED brightness. The brightness levels

are 100% (Fullscale), 70%, 40%, and 20%. When connecting multiple LEDs in parallel to the DKEY current sink,

it is recommended that ballast resistors be placed in series with the LEDs. The ballast resistors help reduce the

affect of LED forward voltage mismatch, and help equalize the diode currents. Ballast resistor values must be

carefully chosen to ensure that the current source headroom voltage is sufficient to supply the desired current.

Please refer to the I²C Compatible Interface section of this datasheet for detailed instructions on how to adjust

the brightness control registers.

MAXIMUM OUTPUT CURRENT, MAXIMUM LED VOLTAGE, MINIMUM INPUT VOLTAGE

The LM27964 can drive 4 LEDs at 30mA each (BankA) and 12 keypad LEDs at 5mA each (60mA total at DKEY)

from an input voltage as low as 3.2V, so long as the LEDs have a forward voltage of 3.6V or less (room

temperature).

The statement above is a simple example of the LED drive capabilities of the LM27964. The statement contains

the key application parameters that are required to validate an LED-drive design using the LM27964: LED

current (I_LEDx), number of active LEDs (N_x), LED forward voltage (V_LED), and minimum input voltage (V_IN-MIN).

The equation below can be used to estimate the maximum output current capability of the LM27964:

I_{LED_MAX}= [(1.5 x V_IN) - V_LED- (I_ADDITIONAL× R_OUT)] / [(N_xx R_OUT) + k_HRx

]

(1)

(2)

I_{LED_MAX}= [(1.5 x V_IN) - V_LED- (I_ADDITIONAL× 2.75Ω)] / [(N_xx 2.75Ω) + k_HRx

]

I_ADDITIONALis the additional current that could be delivered to the other LED banks.

R_OUT– Output resistance. This parameter models the internal losses of the charge pump that result in voltage

droop at the pump output P_OUT. Since the magnitude of the voltage droop is proportional to the total output

current of the charge pump, the loss parameter is modeled as a resistance. The output resistance of the

LM27964 is typically 2.75Ω (V_IN= 3.6V, T_A= 25°C). In equation form:

V_POUT= (1.5 × V_IN) – [(N_A× I_LEDA+ N_B× I_LEDB+ N_K× I_LEDK) × R_OUT

]

(3)

k_HR– Headroom constant. This parameter models the minimum voltage required to be present across the current

sources for them to regulate properly. This minimum voltage is proportional to the programmed LED current, so

the constant has units of mV/mA. The typical k_HRof the LM27964 is 12mV/mA. In equation form:

(V_POUT– V_LEDx) > k_HRx× I_LEDx

Typical Headroom Constant Values

k_HRA= 12mV/mA

(4)

k_HRB= 12 mV/mA

k_HRK= 3 mV/mA

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The "I_LED-MAX" Equation 1 is obtained from combining the R_OUTEquation 3 with the k_HRxEquation 4 and solving

for I_LEDx. Maximum LED current is highly dependent on minimum input voltage and LED forward voltage. Output

current capability can be increased by raising the minimum input voltage of the application, or by selecting an

LED with a lower forward voltage. Excessive power dissipation may also limit output current capability of an

application.

Total Output Current Capability

The maximum output current that can be drawn from the LM27964 is 180mA. Each driver bank has a maximum

allotted current per Dxx sink that must not be exceeded.

Table 2. Driver Bank Maximum Allotted Current per Dxx Sink

DRIVER TYPE

DxA

MAXIMUM Dxx CURRENT

30mA per DxA Pin

30mA per DxB Pin

80mA

DxB

DKEY

The 180mA load can be distributed in many different configurations. Special care must be taken when running

the LM27964 at the maximum output current to ensure proper functionality.

PARALLEL CONNECTED OUTPUTS

Outputs D1A-4A or D1B-D2B may be connected together to drive one or two LEDs at higher currents. In such a

configuration, all four parallel current sinks (BankA) of equal value can drive a single LED. The LED current

programmed for BankA should be chosen so that the current through each of the outputs is programmed to 25%

of the total desired LED current. For example, if 60mA is the desired drive current for a single LED, R_SETAshould

be selected such that the current through each of the current sink inputs is 15mA. Similarly, if two LEDs are to be

driven by pairing up the D1A-4A inputs (i.e D1A-2A, D3A-4A), R_SETAshould be selected such that the current

through each current sink input is 50% of the desired LED current. The same RSETx selection guidelines apply

to BankB diodes.

Connecting the outputs in parallel does not affect internal operation of the LM27964 and has no impact on the

Electrical Characteristics and limits previously presented. The available diode output current, maximum diode

voltage, and all other specifications provided in the Electrical Characteristics table apply to this parallel output

configuration, just as they do to the standard 4-LED application circuit.

Both BankA and BankB utilize LED forward voltage sensing circuitry on each Dxx pin to optimize the charge-

pump gain for maximum efficiency. Due to the nature of the sensing circuitry, it is not recommended to leave any

of the DxA or DxB pins unused if either diode bank is going to be used during normal operation. Leaving DxA

and/or DxB pins unconnected will force the charge-pump into 3/2× mode over the entire V_INrange negating any

efficiency gain that could be achieve by switching to 1× mode at higher input voltages.

Care must be taken when selecting the proper R_SETxvalue. The current on any Dxx pin must not exceed the

maximum current rating for any given current sink pin.

POWER EFFICIENCY

Efficiency of LED drivers is commonly taken to be the ratio of power consumed by the LEDs (P_LED) to the power

drawn at the input of the part (P_IN). With a 1.5x/1x charge pump, the input current is equal to the charge pump

gain times the output current (total LED current). The efficiency of the LM27964 can be predicted as follows:

P_LEDTOTAL= (V_LEDA× N_A× I_LEDA) + (V_LEDB× N_B× I_LEDB) + (V_LEDK× N_K× I_LEDK

)

(5)

(6)

(7)

(8)

P_IN= V_IN× I_IN

P_IN= V_IN× (GAIN × I_LEDTOTAL+ I_Q)

E = (P_LEDTOTAL÷ P_IN)

It is also worth noting that efficiency as defined here is in part dependent on LED voltage. Variation in LED

voltage does not affect power consumed by the circuit and typically does not relate to the brightness of the LED.

For an advanced analysis, it is recommended that power consumed by the circuit (V_INx I_IN) be evaluated rather

than power efficiency.

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POWER DISSIPATION

The power dissipation (P_DISS) and junction temperature (T_J) can be approximated with the equations below. P_INis

the power generated by the 1.5x/1x charge pump, P_LEDis the power consumed by the LEDs, T_Ais the ambient

temperature, and θ_JAis the junction-to-ambient thermal resistance for the WQFN-24 package. V_INis the input

voltage to the LM27964, V_LEDis the nominal LED forward voltage, N is the number of LEDs and I_LEDis the

programmed LED current.

P_DISS= P_IN- P_LEDA- P_LEDB- P_LEDK

(9)

(10)

(11)

P_DISS= (GAIN × V_IN× I_{LEDA + LEDB + LEDK}) - (V_LEDA× N_A× I_LEDA) - (V_LEDB× N_B× I_LEDB) - (V_LEDK× N_K× I_LEDK

)

T_J= T_A+ (P_DISSx θ_JA)

The junction temperature rating takes precedence over the ambient temperature rating. The LM27964 may be

operated outside the ambient temperature rating, so long as the junction temperature of the device does not

exceed the maximum operating rating of 100°C. The maximum ambient temperature rating must be derated in

applications where high power dissipation and/or poor thermal resistance causes the junction temperature to

exceed 100°C.

THERMAL PROTECTION

Internal thermal protection circuitry disables the LM27964 when the junction temperature exceeds 170°C (typ.).

This feature protects the device from being damaged by high die temperatures that might otherwise result from

excessive power dissipation. The device will recover and operate normally when the junction temperature falls

below 165°C (typ.). It is important that the board layout provide good thermal conduction to keep the junction

temperature within the specified operating ratings.

CAPACITOR SELECTION

The LM27964 requires 4 external capacitors for proper operation (C₁= C₂= 1µF, C_IN= C_OUT= 2.2µF). Surface-

mount multi-layer ceramic capacitors are recommended. These capacitors are small, inexpensive and have very

low equivalent series resistance (ESR <20mΩ typ.). Tantalum capacitors, OS-CON capacitors, and aluminum

electrolytic capacitors are not recommended for use with the LM27964 due to their high ESR, as compared to

ceramic capacitors.

For most applications, ceramic capacitors with X7R or X5R temperature characteristic are preferred for use with

the LM27964. These capacitors have tight capacitance tolerance (as good as ±10%) and hold their value over

temperature (X7R: ±15% over -55°C to 125°C; X5R: ±15% over -55°C to 85°C).

Capacitors with Y5V or Z5U temperature characteristic are generally not recommended for use with the

LM27964. Capacitors with these temperature characteristics typically have wide capacitance tolerance (+80%, -

20%) and vary significantly over temperature (Y5V: +22%, -82% over -30°C to +85°C range; Z5U: +22%, -56%

over +10°C to +85°C range). Under some conditions, a nominal 1µF Y5V or Z5U capacitor could have a

capacitance of only 0.1µF. Such detrimental deviation is likely to cause Y5V and Z5U capacitors to fail to meet

the minimum capacitance requirements of the LM27964.

The minimum voltage rating acceptable for all capacitors is 6.3V. The recommended voltage rating of the output

capacitor is 10V to account for DC bias capacitance losses.

PCB LAYOUT CONSIDERATIONS

The WQFN is a leadframe based Chip Scale Package (CSP) with very good thermal properties. This package

has an exposed DAP (die attach pad) at the center of the package measuring 2.6mm x 2.5mm. The main

advantage of this exposed DAP is to offer lower thermal resistance when it is soldered to the thermal land on the

PCB. For PCB layout, TI highly recommends a 1:1 ratio between the package and the PCB thermal land. To

further enhance thermal conductivity, the PCB thermal land may include vias to a ground plane. For more

detailed instructions on mounting WQFN packages, see the TI AN-1187 Application Report (SNOA401).

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REVISION HISTORY

Changes from Revision C (May 2013) to Revision D

Page

•

Changed layout of National Data Sheet to TI format .......................................................................................................... 15

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PACKAGE OPTION ADDENDUM

www.ti.com

7-Oct-2013

PACKAGING INFORMATION

Orderable Device

LM27964SQ-A/NOPB

LM27964SQ-C/NOPB

LM27964SQ-I/NOPB

LM27964SQX-A/NOPB

LM27964SQX-C/NOPB

LM27964SQX-I/NOPB

Status Package Type Package Pins Package

Eco Plan Lead/Ball Finish

MSL Peak Temp

Op Temp (°C)

Device Marking

Samples

Drawing

Qty

(1)

(2)

(3)

(4/5)

ACTIVE

WQFN

RTW

1000

Green (RoHS

& no Sb/Br)

CU SN

Level-1-260C-UNLIM

27964-A

ACTIVE

RTW

1000

4500

Green (RoHS

& no Sb/Br)

27964-C

L27964S

27964-A

27964-C

L27964S

Green (RoHS

& no Sb/Br)

-30 to 85

Green (RoHS

& no Sb/Br)

Green (RoHS

& no Sb/Br)

Green (RoHS

& no Sb/Br)

-30 to 85

⁽¹⁾The marketing status values are defined as follows:

ACTIVE: Product device recommended for new designs.

LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.

NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.

PREVIEW: Device has been announced but is not in production. Samples may or may not be available.

OBSOLETE: TI has discontinued the production of the device.

⁽²⁾Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability

information and additional product content details.

TBD: The Pb-Free/Green conversion plan has not been defined.

Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that

lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.

Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between

the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.

Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight

in homogeneous material)

⁽³⁾MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

⁽⁴⁾There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.

⁽⁵⁾Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation

of the previous line and the two combined represent the entire Device Marking for that device.

Addendum-Page 1

PACKAGE OPTION ADDENDUM

www.ti.com

7-Oct-2013

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information

provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and

continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.

TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

Addendum-Page 2

PACKAGE MATERIALS INFORMATION

www.ti.com

23-Sep-2013

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device

Package Package Pins

Type Drawing

SPQ

Reel

Pin1

Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant

(mm) W1 (mm)

LM27964SQ-A/NOPB

LM27964SQ-C/NOPB

LM27964SQ-I/NOPB

LM27964SQX-A/NOPB

LM27964SQX-C/NOPB

LM27964SQX-I/NOPB

WQFN

RTW

1000

4500

178.0

330.0

12.4

4.3

1.3

8.0

12.0

Pack Materials-Page 1

PACKAGE MATERIALS INFORMATION

www.ti.com

23-Sep-2013

*All dimensions are nominal

Device

Package Type Package Drawing Pins

SPQ

Length (mm) Width (mm) Height (mm)

LM27964SQ-A/NOPB

LM27964SQ-C/NOPB

LM27964SQ-I/NOPB

LM27964SQX-A/NOPB

LM27964SQX-C/NOPB

LM27964SQX-I/NOPB

WQFN

RTW

1000

4500

210.0

367.0

185.0

367.0

35.0

Pack Materials-Page 2

MECHANICAL DATA

RTW0024A

SQA24A (Rev B)

www.ti.com

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LM27964 [TI]

相关型号：

LM27964SQ-A

LM27964SQ-A/NOPB

LM27964SQ-C

LM27964SQ-C/NOPB

LM27964SQ-I

LM27964SQ-I/NOPB

LM27964SQX-A

LM27964SQX-A

LM27964SQX-C

LM27964SQX-C/NOPB

LM27964SQX-I

LM27964SQX-I