May 2003
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 accommodate 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 techniques. 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 2.3µA (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 package.
Features
nRegulated current sources with ±0.5% matching between any two outputs
nHigh efficiency 3/2 boost function
nDrives one, two, three or four white LEDs
n2.7V to 5.5V Input Voltage
nUp to 80mA output current
nAnalog brightness control
nActive-low or high shutdown input (’94/95)
nVery small solution size and no inductor
n2.3µA (typ.) shutdown current
n325kHz switching frequency (min.)
nConstant Frequency generates predictable noise spectrum
nStandard Micro SMD-14 package: 2.08mm X 2.403mm X 0.845mm High
nThin 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
PWM and Analog with Supply LED Capacitor Switched Regulated Current LM2794/LM2795
Control Brightness
© 2003 National Semiconductor Corporation |
DS200285 |
www.national.com |
LM2794/LM2795
Connection Diagram
20028523
Bottom View
Ordering Information
Standard Micro SMD Package:
Order Number |
Shutdown Polarity |
Package Number |
Package |
Supplied As |
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Marking |
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LM2794BL |
Active Low |
BLP14EHB |
I LOG |
250 Units, Tape and Reel |
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LM2794BLX |
Active Low |
BLP14EHB |
I LOG |
3000 Units, Tape and Reel |
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LM2795BL |
Active High |
BLP14EHB |
I LOJ |
250 Units, Tape and Reel |
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LM2795BLX |
Active High |
BLP14EHB |
I LOJ |
3000 Units, Tape and Reel |
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Thin Micro SMD Package: |
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Order Number |
Shutdown Polarity |
Package Number |
Package |
Supplied As |
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Marking |
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LM2794TL |
Active Low |
TLP14EHA |
I LOG |
250 Units, Tape and Reel |
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LM2794TLX |
Active Low |
TLP14EHA |
I LOG |
3000 Units, Tape and Reel |
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LM2795TL |
Active High |
TLP14EHA |
I LOJ |
250 Units, Tape and Reel |
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LM2795TLX |
Active High |
TLP14EHA |
I LOJ |
3000 Units, Tape and Reel |
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Pin Description
Pin(*) |
Name |
Function |
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A1 |
C1+ |
Positive terminal of C1 |
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B2 |
C1− |
Negative terminal of C1 |
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C1 |
VIN |
Power supply voltage input |
D2 |
GND |
Power supply ground input |
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E1 |
C2− |
Negative terminal of C2 |
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E3,E5,E7,D6 |
D1−4 |
Current source outputs. Connect directly to LED |
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C7 |
ISET |
Current Sense Input. Connect 1% resistor to ground to set constant current through LED |
B6 |
BRGT |
Variable voltage input controls output current |
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A7 |
SD |
The LM2794 has an active-low shutdown pin (LOW = shutdown, HIGH = operating). The |
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LM2795 has an active-high shutdown pin (HIGH = shutdown, LOW = operating) that has a |
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pull-up to VIN. |
A5 |
C2+ |
Positive terminal of C2 |
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A3 |
POUT |
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, C1as pin 2, VIN as pin 3, GND as pin 4, C2as 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
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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.
VIN |
−0.5 to 6.2V max |
SD |
−0.5 to (VIN+0.3V) w/ |
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6.2V max |
BRGT |
−0.5 to (VIN+0.3V) w/ |
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6.2V max |
Continuous Power Dissipation |
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(Note 2) |
Internally Limited |
TJMAX (Note 2) |
135˚C |
θJA (Notes 2, 3) |
125˚C/W |
Storge Temperature |
−65˚C to +150˚C |
Lead Temp. (Soldering, 5 sec.) |
260˚C |
ESD Rating (Note 4) |
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Human Body Model |
2kV |
Machine Model |
200V |
Operating Conditions
Input Voltage (VIN) |
2.7V to 5.5V |
Ambient Temperature (TA) |
−30˚C to +85˚C |
Junction Temperature (TJ) |
−30˚C to +100˚C |
Electrical Characteristics
Limits in standard typeface are for TJ = 25˚C and limits in boldface type apply over the full Operating Junction Temperature
Range (−30˚C ≤ TJ ≤ +100˚C). Unless otherwise specified, C1 = C2 = CIN = CHOLD = 1 µF, VIN = 3.6V, BRGT pin = 0V; RSET =124Ω ; LM2794:VSD = VIN (LM2795: VSD = 0V).
Symbol |
Parameter |
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Conditions |
Min |
Typ |
Max |
Units |
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IDX |
Available Current at Output Dx |
3.0V |
≤ VIN ≤ 5.5V |
15 |
16.8 |
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mA |
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VDX ≤ 3.8V |
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BRGT = 50mV |
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2.7V |
≤ VIN ≤ 3.0V |
10 |
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VDX ≤ 3.6V |
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mA |
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BRGT = 0V |
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VDX ≤ 3.8V |
20 |
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mA |
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BRGT = 200mV |
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VDX |
Available Voltage at Output Dx |
3.0V |
≤ VIN ≤ 5.5V |
3.8 |
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V |
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IDX ≤ 15mA |
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BRGT = 50mV |
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IDX |
Line Regulation of Dx Output |
3.0V |
≤ VIN ≤ 5.5V |
14.18 |
15.25 |
16.78 |
mA |
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Current |
VDX = 3.6V |
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3.0V |
≤ VIN ≤ 4.4V |
14.18 |
15.25 |
16.32 |
mA |
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VDX = 3.6V |
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IDX |
Load Regulation of Dx Output |
VIN = 3.6V |
14.18 |
15.25 |
16.32 |
mA |
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Current |
3.0V |
≤ VDX ≤ 3.8V |
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ID-MATCH |
Current Matching Between Any |
VIN = 3.6V, VDX = 3.6V |
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0.5 |
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% |
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Two Outputs |
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IQ |
Quiescent Supply Current |
3.0V |
≤ VIN ≤ 4.2V, Active, No |
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5.5 |
8.2 |
mA |
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Load Current |
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RSET = OPEN |
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ISD |
Shutdown Supply Current |
3.0V |
≤ VIN ≤ 5.5V, Shutdown |
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2.3 |
5 |
µA |
IPULL-SD |
Shutdown Pull-Up Current |
VIN = 3.6V |
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1.5 |
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µA |
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(LM2795) |
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VCP |
Input Charge-Pump Mode To |
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4.7 |
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V |
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Pass Mode Threshold |
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VCPH |
Input Charge-Pump Mode To |
(Note 5) |
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250 |
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mV |
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Pass Mode Hysteresis |
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VIH |
SD Input Logic High (LM2794) |
3.0V |
≤ VIN ≤ 5.5V |
1.0 |
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V |
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SD Input Logic High (LM2795) |
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0.8VIN |
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VIL |
SD Input Logic Low (LM2794) |
3.0V |
≤ VIN ≤ 5.5V |
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0.2 |
V |
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SD Input Logic Low (LM2795) |
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0.2VIN |
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ILEAK-SD |
SD Input Leakage Current |
0V ≤ VSD ≤ VIN |
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100 |
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nA |
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RBRGT |
BRGT Input Resistance |
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240 |
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kΩ |
ISET |
ISET Pin Output Current |
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IDX/10 |
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mA |
LM2794/LM2795
3 |
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LM2794/LM2795
Electrical Characteristics (Continued)
Limits in standard typeface are for TJ = 25˚C and limits in boldface type apply over the full Operating Junction Temperature
Range (−30˚C ≤ TJ ≤ +100˚C). Unless otherwise specified, C1 = C2 = CIN = CHOLD = 1 µF, VIN = 3.6V, BRGT pin = 0V; RSET =124Ω ; LM2794:VSD = VIN (LM2795: VSD = 0V).
Symbol |
Parameter |
Conditions |
Min |
Typ |
Max |
Units |
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fSW |
Switching Frequency (Note 6) |
3.0V ≤ VIN ≤ 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 TJ=150˚C (typ.) and disengages at TJ=140˚C (typ.). D1, D2, D3 and D4 may be shorted to GND without damage. POUT may be shorted to GND for 1sec without damage.
Note 3: The value of θJA is based on a two layer evaluation board with a dimension of 2in. x1.5in.
Note 4: In the test circuit, all capacitors are 1.0µF, 0.3Ω 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, fOSC = 1/8fSW.
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4 |
Typical Performance Characteristics Unless otherwise specified, C1 = C2 = CIN = CHOLD = 1µF, VIN = 3.6V, BRGT pin = 0V, RSET = 124Ω.
IDIODE vs VIN |
IDIODE vs BRGT |
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20028512 |
20028509 |
IDIODE vs VIN |
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BRGT = 3V |
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IDIODE vs RSET |
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20028507 |
20028508 |
IDIODE vs RSET |
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VBRGT = 0V |
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IDIODE vs VDIODE |
20028524
20028541
LM2794/LM2795
5 |
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LM2794/LM2795
Typical Performance Characteristics Unless otherwise specified, C1 = C2 = CIN = CHOLD = 1µF, VIN = 3.6V, BRGT pin = 0V, RSET = 124Ω. (Continued)
VSET vs VBRGT |
Duty Cycle vs. Led Current (LM2794) |
RSET = 1KΩ |
IDIODE 1- 4 = 15mA |
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20028506 |
20028532 |
Supply Current vs VIN |
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Supply Current vs VIN |
IDIODE 1-4 = 15mA |
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IDIODE 1-4 = Open |
20028514 |
20028515 |
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Shutdown Supply Current vs VIN |
Shutdown Threshold vs VIN |
20028505
20028513
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6 |
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