LM2794/LM2795
Current Regulated Switched Capacitor LED Supply with
Analog and PWM Brightness Control
General Description
The LM2794/95 is a fractional CMOS charge-pump that
provides four regulated current sources. It accepts an input
voltage range from 2.7V to 5.5V and maintains a constant
current determined by an external sense resistor.
The LM2794/5 delivers up to 80mA of load current to accom-
modate four White LEDs. The switching frequency is
325kHz. (min.) to keep the conducted noise spectrum away
from sensitive frequencies within portable RF devices.
Brightness can be controlled by both linear and PWM tech-
niques. A voltage between 0V and 3.0V may be applied to
the BRGT pin to linearly vary the LED current. Alternatively,
a PWM signal can be applied to the SD pin to vary the
perceived brightness of the LED. The SD pin reduces the
operating current to 2.3A (typ.) The LM2794 is shut down
when the SD pin is low, and the LM2795 is shut down when
the SD pin is high.
The LM2794/95 is available in a micro SMD-14 CSP pack-
age.
Features
n
Regulated current sources with
0.5% matching
between any two outputs
n
High efficiency 3/2 boost function
n
Drives one, two, three or four white LEDs
n
2.7V to 5.5V Input Voltage
n
Up to 80mA output current
n
Analog brightness control
n
Active-low or high shutdown input ('94/95)
n
Very small solution size and no inductor
n
2.3A (typ.) shutdown current
n
325kHz switching frequency (min.)
n
Constant Frequency generates predictable noise
spectrum
n
Standard Micro SMD-14 package: 2.08mm X 2.403mm
X 0.845mm High
n
Thin Micro SMD-14 package: 2.08mm X 2.403mm X
0.600mm High
Applications
n
White LED Display Backlights
n
White LED Keypad Backlights
n
1-Cell Li-Ion battery-operated equipment including
PDAs, hand-held PCs, cellular phones
Basic Application Circuit
20028503
March 2004
LM2794/LM2795
Current
Regulated
Switched
Capacitor
LED
Supply
with
Analog
and
PWM
Brightness
Control
2004 National Semiconductor Corporation
DS200285
www.national.com
Connection Diagram
20028523
Bottom View
Ordering Information
Standard Micro SMD Package:
Order Number
Shutdown Polarity
Package Number
Package
Marking
Supplied As
LM2794BL
Active Low
BLP14EHB
I LOG
250 Units, Tape and Reel
LM2794BLX
Active Low
BLP14EHB
I LOG
3000 Units, Tape and Reel
LM2795BL
Active High
BLP14EHB
I LOJ
250 Units, Tape and Reel
LM2795BLX
Active High
BLP14EHB
I LOJ
3000 Units, Tape and Reel
Thin Micro SMD Package:
Order Number
Shutdown Polarity
Package Number
Package
Marking
Supplied As
LM2794TL
Active Low
TLP14EHA
I LOG
250 Units, Tape and Reel
LM2794TLX
Active Low
TLP14EHA
I LOG
3000 Units, Tape and Reel
LM2795TL
Active High
TLP14EHA
I LOJ
250 Units, Tape and Reel
LM2795TLX
Active High
TLP14EHA
I LOJ
3000 Units, Tape and Reel
Pin Description
Pin(*)
Name
Function
A1
C1+
Positive terminal of C1
B2
C1-
Negative terminal of C1
C1
V
IN
Power supply voltage input
D2
GND
Power supply ground input
E1
C2-
Negative terminal of C2
E3,E5,E7,D6
D1-4
Current source outputs. Connect directly to LED
C7
I
SET
Current Sense Input. Connect 1% resistor to ground to set constant current through LED
B6
BRGT
Variable voltage input controls output current
A7
SD
The LM2794 has an active-low shutdown pin (LOW = shutdown, HIGH = operating). The
LM2795 has an active-high shutdown pin (HIGH = shutdown, LOW = operating) that has a
pull-up to V
IN
.
A5
C2+
Positive terminal of C2
A3
P
OUT
Charge pump output
(*) Note that the pin numbering scheme for the Micro SMD package was revised in April, 2002 to conform to JEDEC standard. Only the pin numbers were revised.
No changes to the physical location of the inputs/outputs were made. For reference purpose, the obsolete numbering had C1+ as pin 1, C1- as pin 2, VIN as pin
3, GND as pin 4, C2- as pin 5, D1-D4 as pin 6,7,8 & 9, Iset as pin 10, BRGT as pin 11, SD as pin 12, C2+ as pin 13, Pout as pin 14
LM2794/LM2795
www.national.com
2
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
V
IN
-0.5 to 6.2V max
SD
-0.5 to (V
IN
+0.3V) w/
6.2V max
BRGT
-0.5 to (V
IN
+0.3V) w/
6.2V max
Continuous Power Dissipation
(Note 2)
Internally Limited
T
JMAX
(Note 2)
135C
JA
(Notes 2, 3)
125C/W
Storge Temperature
-65C to +150C
Lead Temp. (Soldering, 5 sec.)
260C
ESD Rating (Note 4)
Human Body Model
2kV
Machine Model
200V
Operating Conditions
Input Voltage (V
IN
)
2.7V to 5.5V
Ambient Temperature (T
A
)
-30C to +85C
Junction Temperature (T
J
)
-30C to +100C
Electrical Characteristics
Limits in standard typeface are for T
J
= 25C and limits in boldface type apply over the full Operating Junction Temperature
Range (-30C
T
J
+100C). Unless otherwise specified, C1 = C2 = C
IN
= C
HOLD
= 1 F, V
IN
= 3.6V, BRGT pin = 0V; R
SET
=124
; LM2794:V
SD
= V
IN
(LM2795: V
SD
= 0V).
Symbol
Parameter
Conditions
Min
Typ
Max
Units
I
DX
Available Current at Output Dx
3.0V
V
IN
5.5V
V
DX
3.8V
BRGT = 50mV
15
16.8
mA
2.7V
V
IN
3.0V
V
DX
3.6V
BRGT = 0V
10
mA
V
DX
3.8V
BRGT = 200mV
20
mA
V
DX
Available Voltage at Output Dx
3.0V
V
IN
5.5V
I
DX
15mA
BRGT = 50mV
3.8
V
I
DX
Line Regulation of Dx Output
Current
3.0V
V
IN
5.5V
V
DX
= 3.6V
14.18
15.25
16.78
mA
3.0V
V
IN
4.4V
V
DX
= 3.6V
14.18
15.25
16.32
mA
I
DX
Load Regulation of Dx Output
Current
V
IN
= 3.6V
3.0V
V
DX
3.8V
14.18
15.25
16.32
mA
I
D-MATCH
Current Matching Between Any
Two Outputs
V
IN
= 3.6V, V
DX
= 3.6V
0.5
%
I
Q
Quiescent Supply Current
3.0V
V
IN
4.2V, Active, No
Load Current
R
SET
= OPEN
5.5
8.2
mA
I
SD
Shutdown Supply Current
3.0V
V
IN
5.5V, Shutdown
2.3
5
A
I
PULL-SD
Shutdown Pull-Up Current
(LM2795)
V
IN
= 3.6V
1.5
A
V
CP
Input Charge-Pump Mode To
Pass Mode Threshold
4.7
V
V
CPH
Input Charge-Pump Mode To
Pass Mode Hysteresis
(Note 5)
250
mV
V
IH
SD Input Logic High (LM2794)
3.0V
V
IN
5.5V
1.0
V
SD Input Logic High (LM2795)
0.8V
IN
V
IL
SD Input Logic Low (LM2794)
3.0V
V
IN
5.5V
0.2
V
SD Input Logic Low (LM2795)
0.2V
IN
I
LEAK-SD
SD Input Leakage Current
0V
V
SD
V
IN
100
nA
R
BRGT
BRGT Input Resistance
240
k
I
SET
I
SET
Pin Output Current
I
DX
/10
mA
LM2794/LM2795
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3
Electrical Characteristics
(Continued)
Limits in standard typeface are for T
J
= 25C and limits in boldface type apply over the full Operating Junction Temperature
Range (-30C
T
J
+100C). Unless otherwise specified, C1 = C2 = C
IN
= C
HOLD
= 1 F, V
IN
= 3.6V, BRGT pin = 0V; R
SET
=124
; LM2794:V
SD
= V
IN
(LM2795: V
SD
= 0V).
Symbol
Parameter
Conditions
Min
Typ
Max
Units
f
SW
Switching Frequency (Note 6)
3.0V
V
IN
4.4V
325
515
675
kHz
Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device
beyond its rated operating conditions.
Note 2: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at T
J
=150C (typ.) and disengages at
T
J
=140C (typ.). D1, D2, D3 and D4 may be shorted to GND without damage. P
OUT
may be shorted to GND for 1sec without damage.
Note 3: The value of
JA
is based on a two layer evaluation board with a dimension of 2in. x1.5in.
Note 4: In the test circuit, all capacitors are 1.0F, 0.3
maximum ESR capacitors. Capacitors with higher ESR will increase output resistance, reduce output
voltage and efficiency.
Note 5: Voltage at which the device switches from charge-pump mode to pass mode or pass mode to charge-pump mode. For example, during pass mode the
device output (Pout) follows the input voltage.
Note 6: The output switches operate at one eigth of the oscillator frequency, f
OSC
= 1/8f
SW
.
LM2794/LM2795
www.national.com
4
Typical Performance Characteristics
Unless otherwise specified, C1 = C2 = C
IN
= C
HOLD
= 1F,
V
IN
= 3.6V, BRGT pin = 0V, R
SET
= 124
.
I
DIODE
vs V
IN
I
DIODE
vs BRGT
20028512
20028509
I
DIODE
vs V
IN
BRGT = 3V
I
DIODE
vs R
SET
20028507
20028508
I
DIODE
vs R
SET
V
BRGT
= 0V
I
DIODE
vs V
DIODE
20028541
20028524
LM2794/LM2795
www.national.com
5
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