LM27953
White LED Driver with Four LED Current Sinks and 3/2x
Switched Capacitor Boost
General Description
The LM27953 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. Regu-
lated internal current sources deliver excellent current and
brightness matching in all LEDs.
The LED driver current sinks can be used to backlight a main
phone display with up to 4 LEDs. The low-side current
drivers accommodate common-anode-type LEDs. The cur-
rent sinks can also drive standard two-terminal LEDs, and
provide other general lighting functions (keypad lighting, fun
lighting, etc). The brightness of the LEDs can be adjusted
independently with an external resistor.
The LM27953 works off an extended Li-Ion input voltage
range (2.7V to 5.5V). Voltage boost is achieved with a high-
efficiency 3/2x-gain charge pump.
The LM27953 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
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
20128001
November 2004
LM27953
White
LED
Driver
with
Four
LED
Current
Sinks
and
3/2x
Switched
Capacitor
Boost
2004 National Semiconductor Corporation
DS201280
www.national.com
Connection Diagram
18-Bump Thin Micro SMD Package, Large Bump
NS Package Number TLA18
20128002
Pin Description
Pin #s
Pin Names
Pin Descriptions
C1
V
IN
Input voltage. Input range: 2.7V to 5.5V.
D2
PWR GND
Power Ground
A3
PWR P
OUT
Charge pump output. Approximately 1.5xV
IN
A1, B2, A5, E1
C1+, C1-, C2+,
C2-
Flying capacitor connections.
D6, E5, D4, E3
D1, D2, D3, D4
LED Outputs - Group A
C5, B4, C3
SIG P
OUT
Signal P
OUT
: Tie pins externally to PWR P
OUT
B6
EN
Enable for Charge Pump and LEDs (current outputs). Logic input.
High = LEDs ON. Low = LEDs OFF.
Pulsing this pin with a PWM signal (100Hz-1kHz) can be used to dim LEDs.
A7
SIG GND
Signal Ground. Tie pin externally to PWR GND
E7
I
SET
Placing a resistor (R
SET
) between this pin and GND sets the LED current. LED
Current = 100 x (1.25V R
SET
).
C7
NC
No Connect
Operational States
EN
Mode of Operation
L
Shutdown
H
Charge Pump Enabled. LEDs ON.
Ordering Information
Order Information
Package
Supplied As
LM27953TL
TLA18 Micro SMD
250 Units, Tape & Reel
LM27953TLX
3000 Units, Tape & Reel
LM27953
www.national.com
2
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.
V
IN
pin voltage
-0.3V to 7.1V
EN pin voltages
-0.3V to (V
IN
+0.3V)
w/ 6.0V max
I
Dx
Pin Voltages
-0.3V to
(V
POUT
+0.3V)
w/ 6.0V max
Continuous Power Dissipation
(Note 3)
Internally Limited
Junction Temperature (T
J-MAX
)
150
o
C
Storage Temperature Range
-65
o
C to +150
o
C
Maximum Lead Temperature
(Soldering, 10 sec.)
265
o
C
ESD Rating (Note 4)
Human Body Model - I
Dx
Pins:
Human Body Model - All other Pins:
Machine Model - I
Dx
Pins:
Machine Model - All Other Pins:
1.0kV
2.0kV
100V
200V
Operating Rating
(Notes 1, 2)
Input Voltage Range
2.7V to 5.5V
Junction Temperature (T
J
) Range
-30C to +125C
Ambient Temperature (T
A
) Range
(Note 5)
-30C to +85C
Thermal Properties
Juntion-to-Ambient Thermal
Resistance (
JA
), (Note 6)
100C/W
Electrical Characteristics
(Notes 2, 7)
Limits in standard typeface are for T
J
= 25C, and limits in boldface type apply over the full operating temperature range. Un-
less otherwise specified: V
IN
= 3.6V; V
Dx
= 0.6V; EN = 1.5V; R
SET
= 8.35k
; C
IN
, C
1
, C
2
, and C
POUT
= 1F. (Note 8)
Symbol
Parameter
Condition
Min
Typ
Max
Units
I
Dx
Output Current Regulation
3.0V
V
IN
4.2V, and V
IN
= 5.5V
0.45V
V
Dx
3.8V
R
SET
= 8.35k
13.5
(-10%)
15
16.5
(+10%)
mA
(%)
3.0V
V
IN
5.5V;
0.6V
V
Dx
3.8V
R
SET
= 6.25k
20
mA
3.0V
V
IN
5.5V;
0.3V
V
Dx
3.8V
R
SET
= 12.5k
10
mA
2.7V
V
IN
3.0V;
0.45V
V
Dx
3.8V
R
SET
= 8.35k
15
mA
I
Dx-MATCH
Current Matching Between
Outputs
V
IN
= 3.0V (Note 9)
0.6
%
I
Q
Quiescent Supply Current
2.7V
V
IN
4.2V;
No Load Current,
EN = ON
4.4
6.75
mA
I
SD
Shutdown Supply Current
2.7V
V
IN
5.5V,
ENA OFF
2.3
5
A
V
SET
I
SET
Pin Voltage
2.7V
V
IN
5.5V
1.25
V
I
Dx
/I
SET
Output Current to Current Set
Ratio
100
R
OUT
Charge Pump Output Resistance
(Note 10)
V
IN
= 3.0V
2.7
V
HR
Current Source Headroom
Voltage Requirement (Note 11)
I
Dx
= 95% X I
Dx
(nom)
R
SET
= 8.35k
(I
Dx
(nom)
15mA)
320
mV
f
SW
Switching Frequency
3.0V
V
IN
4.2V
375
500
625
kHz
LM27953
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3
Electrical Characteristics
(Notes 2, 7) (Continued)
Limits in standard typeface are for T
J
= 25C, and limits in boldface type apply over the full operating temperature range. Un-
less otherwise specified: V
IN
= 3.6V; V
Dx
= 0.6V; EN = 1.5V; R
SET
= 8.35k
; C
IN
, C
1
, C
2
, and C
POUT
= 1F. (Note 8)
Symbol
Parameter
Condition
Min
Typ
Max
Units
t
START
Start-up Time
I
Dx
= 90% steady state
350
s
1.5x/1x
Charge pump gain cross-over:
Gain = 1.5 when V
IN
is below
threshold. Gain = 1 when V
IN
is
above threshold.
1.5x to 1x Threshold
4.75
V
1x to 1.5x Threshold
4.55
V
Logic Pin Specifications: EN
V
IL
Input Logic Low
2.7V
V
IN
5.5V
0
0.5
V
V
IH
Input Logic High
2.7V
V
IN
5.5V
1.1
V
IN
V
I
LEAK
Input Leakage Current
V
EN
= 0V
0.1
A
V
EN
= 3V (Note 12)
10
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
J
= 160C (typ.) and disengages at T
J
=
120C (typ.). The thermal shutdown function is guaranteed by design.
Note 4: The Human body model is a 100pF capacitor discharged through a 1.5k
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
A-MAX
) is dependent on the maximum operating junction temperature (T
J-MAX-OP
= 125C), 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 (
JA
), as given by the
following equation: T
A-MAX
= T
J-MAX-OP
(
JA
x P
D-MAX
).
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
IN
, C
POUT
, C
1
, and C
2
: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics
Note 9: For the group of outputs on a part, 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 the 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 typical specification provided is the most likely norm of the matching figure for
all parts.
Note 10: Output resistance (R
OUT
) models all voltage losses in the charge pump. R
OUT
can be used to estimate the voltage at the charge pump output (P
OUT
):
V
Pout
= (1.5 x V
IN
) (R
OUT
x I
OUT
). In the equation, I
OUT
is the total output current: the sum of all active Dxx output currents and all current drawn from P
OUT
. The
equation applies when the charge pump is operating with a gain of 3/2 (V
IN
4.75V typ.).
Note 11: Headroom voltage: V
HR
= V
Pout
V
LEDx
. If headroom voltage requirement is not met, LED current regulation will be compromised.
Note 12: There is a 300k
(typ.) pull-down resistor connected internally between the enable pin (EN) and GND.
LM27953
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4
Typical Performance Characteristics
Unless otherwise specified: V
IN
= 3.6V; V
LED
= 3.6V; EN =
V
IN
; R
SET
= 8.35k
; C
IN
, C
1
, C
2
, and C
POUT
= 1F.
LED Current (D1, D2,D3, D4)
vs. Input Voltage
LED Current (Dx) vs. Input Voltage
20128004
20128005
Quiescent Current vs. Input Voltage,
Charge Pump Output Voltage
vs. Output Current
20128006
20128007
LM27953
www.national.com
5
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