National Semiconductor LM27961 Technical data

LM27961
Dual-Display White LED Driver with 3/2x Switched
Capacitor Boost

LM27961 Dual-Display White LED Driver with 3/2x Switched Capacitor Boost

November 2004

General Description

The LM27961 is a charge-pump-based white-LED driver that
is ideal for mobile phone display backlighting. It is intended
to drive 4 LEDs for a main phone display backlight and 3
LEDs for a sub-display backlight. Regulated internal current
sources deliver excellent current and brightness matching in
all LEDs.

The LED driver current sources are split into two indepen­dently controlled groups. The primary group (Group A) can
be used to backlight a main phone display with up to 4 LEDs.
The low-side current drivers of Group A accommodate
common-anode-type LEDs. The second group (Group B)
can backlight a secondary display with up to 3 LEDs. The
high-side current drivers of Group B accommodate common­cathode-type LEDs. Both Group A and Group B can also
drive standard two-terminal LEDs, and provide other general
lighting functions (keypad lighting, fun lighting, etc). The
brightness of the two LED groups can be adjusted indepen­dently with external resistors.

The LM27961 works off an extended Li-Ion input voltage
range (2.7V to 5.5V). Voltage boost is achieved with a high­efficiency 3/2x-gain charge pump.

The LM27961 is available in National’s chip-scale 18-bump
micro SMD package.

Features

n Drives 4 Individual Common-Anode LEDs with up to

20mA each for a Main Display Backlight

n Drives 3 Individual Common-Cathode LEDs with up to

20mA each for a Sub-Display Backlight

n Independent Resistor-Programmable Current Setting
n Excellent Current and Brightness Matching
n High-Efficiency 3/2x Charge Pump
n Extended Li-Ion Input: 2.7V to 5.5V
n PWM Brightness Control: 100Hz - 1kHz
n 18-bump Thin Micro SMD Package:

(2.1mm x 2.4mm x 0.6mm)

Applications

n Mobile Phone Display Lighting
n Mobile Phone Keypad Lighting
n PDAs
n General LED Lighting

Typical Application Circuit

20127901

© 2004 National Semiconductor Corporation DS201279 www.national.com

Connection Diagram

LM27961

Pin Description

Pin #s Pin Names Pin Descriptions

C1 V

D2 GND Ground

A3 P

A1, B2, A5, E1 C1+, C1-, C2+,

D6, E5, D4, E3 D1A, D2A, D3A,

C5, B4, C3 D1B, D2B, D3B LED Outputs - Group B

B6 EN-A Enable for Group-A LEDs (current outputs). Logic input.

A7 EN-B Enable for Group-B LEDs (current outputs). Logic input.

E7 I

C7 I

18-Bump Thin Micro SMD Package, Large Bump

NS Package Number TLA18

IN

OUT

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

Charge pump output. Approximately 1.5xV

Flying capacitor connections.

C2-

LED Outputs - Group A

D4A

High = Group-A LEDs ON. Low = Group A LEDs OFF.
Pulsing this pin with a PWM signal (100Hz-1kHz) can be used to dim LEDs.

High = Group-B LEDs ON. Low = Group B LEDs OFF.
Pulsing this pin with a PWM signal (100Hz-1kHz) can be used to dim LEDs.

SETA

Placing a resistor (R

SETA

Group A LEDs. LED Current = 100 x (1.25V ÷ R

SETB

Placing a resistor (R

SETB

Group B LEDs. LED Current = 100 x (1.25V ÷ R

20127902

IN

) between this pin and GND sets the LED current for

).

SETA

) between this pin and GND sets the LED current for

).

SETB

Operational States

ENA ENB Mode of Operation

L L Shutdown

H L Enabled. Group A LEDs ON. Group B LEDs OFF

L H Enabled. Group B LEDs ON. Group A LEDs OFF

H H Invalid for normal operation

Ordering Information

Order Information Package Supplied As

LM27961TL TLA18 Micro SMD 250 Units, Tape & Reel

LM27961TLX 3000 Units, Tape & Reel

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LM27961

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.

pin voltage -0.3V to 7.1V

V

IN

ENA, ENB pin voltages -0.3V to (V

+0.3V)

IN

Operating Rating (Notes 1, 2)

Input Voltage Range 2.7V to 5.5V

Junction Temperature (T

Ambient Temperature (T
(Note 5)

) Range -30˚C to +125˚C

J

) Range

A

-30˚C to +85˚C

w/ 6.0V max

Pin Voltages -0.3V to

I

Dxx

(V

POUT

w/ 6.0V max

Continuous Power Dissipation

Internally Limited

+0.3V)

Thermal Properties

Juntion-to-Ambient Thermal
Resistance (θ

), (Note 6)

JA

100˚C/W

(Note 3)

Junction Temperature (T

Storage Temperature Range -65

Maximum Lead Temperature

) 150oC

J-MAX

o

C to +150oC

265

o

C

(Soldering, 10 sec.)

ESD Rating (Note 4)
Human Body Model - I
Human Body Model - All other Pins:
Machine Model - I

Dxx

Machine Model - All Other Pins:

Dxx

Pins:

Pins:

1.0kV

2.0kV
100V
200V

Electrical Characteristics (Notes 2, 7)

Limits in standard typeface are for TJ= 25˚C, and limits in boldface type apply over the full operating temperature range. Un­less otherwise specified: V

1.5V; R

SETA=RSETB

pins (I

Dxx

and I

) apply to both Group A and Group B. (Note 8)

SETx

= 3.6V; V

IN

= 8.35kΩ;CIN,C1,C2, and C

Symbol Parameter Condition Min Typ Max Units

I

Dxx

I

Dxx-MATCH

Output Current Regulation

Current Matching Between Any
Two Group A Outputs or Group
B Outputs

I

Q

I

SD

V

SET

I

Dxx/ISET

Quiescent Supply Current 2.7V ≤ VIN≤ 4.2V;

Shutdown Supply Current 2.7V ≤ VIN≤ 5.5V,

I

Pin Voltage 2.7V ≤ VIN≤ 5.5V 1.25 V

SET

Output Current to Current Set
Ratio

= 0.6V; V

DxA

DxB

POUT

3.0V ≤ V

0.45V ≤ V

2.5V ≤ V
= 8.35kΩ

R

SET

3.0V ≤ V

0.6V ≤ V

2.5V ≤ V
= 6.25kΩ

R

SET

3.0V ≤ V

0.3V ≤ V

2.5V ≤ V
= 12.5kΩ

R

SET

2.7V ≤ V

0.45V ≤ V

2.5V ≤ V
= 8.35kΩ

R

SET

= 3.0V (Note 9) 0.6 %

V

IN

No Load Current,
ENA or ENB = ON

ENA and ENB = OFF

= 3.6V; ENA = 1.5V and ENB = GND, or ENA = GND and ENB =

= 1µF. Specifications related to output current(s) and current setting

≤ 4.2V, and VIN= 5.5V

IN

DxA

DxB

≤ 5.5V;

IN

DxA

DxB

≤ 5.5V;

IN

DxA

DxB

≤ 3.0V;

IN

DxA

DxB

≤ 3.8V or

≤ 3.8V;

≤ 3.8V or
≤ 3.8V;

≤ 3.8V or
≤ 3.8V;

≤ 3.8V or

≤ 3.8V;

13.5

(-10%)

15

16.5

(+10%)mA(%)

20 mA

10 mA

15 mA

4.4 6.75 mA

2.3 5 µA

100

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Electrical Characteristics (Notes 2, 7) (Continued)

Limits in standard typeface are for TJ= 25˚C, and limits in boldface type apply over the full operating temperature range. Un-

LM27961

less otherwise specified: V

Dxx

SETA

=R

and I

SETB

) apply to both Group A and Group B. (Note 8)

SETx

1.5V; R
pins (I

Symbol Parameter Condition Min Typ Max Units

R

OUT

Charge Pump Output Resistance
(Note 10)

V

HR

Current Source Headroom
Voltage Requirement (Note 11)

f

SW

t

START

Switching Frequency 3.0V ≤ VIN≤ 4.2V 375 500 625 kHz

Start-up Time IDx= 90% steady state 350 µs

1.5x/1x Charge pump gain cross-over:
Gain = 1.5 when VINis below
threshold. Gain = 1 when V
above threshold.

Logic Pin Specifications: EN, ENA, ENB

V

IL

V

IH

I

LEAK

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 pin.

Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at T

120˚C (typ.). The thermal shutdown function is guaranteed by design.

Note 4: The Human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. The machine model is a 200pF capacitor discharged
directly into each pin. MIL-STD-883 3015.7

Note 5: 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 6: 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.

Note 7: 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 8: C

Note 9: For the two groups of outputs on a part (GroupA and Group B), 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 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 10: Output resistance (R
V

Pout

equation applies when the charge pump is operating with a gain of 3/2 (V

Note 11: Headroom voltage: V

Note 12: There is a 300kΩ(typ.) pull-down resistor connected internally between each enable pin (ENA, ENB) and GND.

Input Logic Low 2.7V ≤ VIN≤ 5.5V 0 0.5 V

Input Logic High 2.7V ≤ VIN≤ 5.5V 1.1 V

Input Leakage Current V

A-MAX=TJ-MAX-OP

IN,CPOUT,C1

=(1.5xVIN)–(R

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

OUTxIOUT

= 3.6V; V

IN

= 8.35kΩ;CIN,C1,C2, and C

DxA

= 0.6V; V

DxB

POUT

VIN= 3.0V 2.7 Ω

I

=95%XI

Dxx

= 8.35kΩ

R

SET

(nom) ≈ 15mA)

(I

Dxx

1.5x to 1x Threshold 4.75 V

is

1x to 1.5x Threshold 4.55 V

IN

= 0V 0.1 µA

ENx

V

= 3V (Note 12) 10

ENx

) 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

–(θJAxP

) models all voltage losses in the charge pump. R

OUT

). In the equation, I

HR=VPout–VLEDx

).

D-MAX

is the total output current: the sum of all active Dxx output currents and all current drawn from P

OUT

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

= 3.6V; ENA = 1.5V and ENB = GND, or ENA = GND and ENB =

= 1µF. Specifications related to output current(s) and current setting

(nom)

Dxx

≤ 4.75V typ.).

IN

J

J-MAX-OP

can be used to estimate the voltage at the charge pump output (P

OUT

320 mV

IN

= 160˚C (typ.) and disengages at TJ=

= 125˚C), the maximum power

OUT

V

OUT

. The

):

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