PAM PAM2805

PAM2805
3-Modes/3W WLED Driver with 1 or 2 Cell Battery
Features
General Descriptio n
n 3 Modes Cycling Function:
The PAM2805 is a step-up DC-DC WLED driver
with 3 modes cycling function(100%
brightness,25% brightness and 8.5Hz blinking).
Power Off
<5S
Power Off
<5S
Dimming
Blinking
Power Off
<5S
Bright
The un i qu e 3 mo de s c y cl i n g fu n ct i on ca n
eliminate the needs of extra functional MCU or IC.
n Reset to Bright mode if Power Off time
more than 5S
n Adjustable Output Current: up to 750mA
n 8.5Hz Blinking Mode
n Low Start-Up Voltage: 0.9V(Typ.)
n Low SW on Resis tanc e: 1 00mΩ
n Over Temperature Protection
n Over Voltage Protection
n SOT23-6 Package
n Pb-Free Package
The PAM2805 can deliver up to 750mA output
current by setting an external resistor.
The PAM2805 switches at a 1.0MHz constant
frequency, allowing for the use of small value
external inductor and ceramic capacitors.
A low 95mV feedback voltage reduces the power
loss in the Rs for better efficiency. With its internal
2A, 100 mΩ NMOS switch, the device can provide
high efficiency even at heavy load.
Applications
n White LED Torch (Flashlight)
The PAM2805 is available in SOT23-6 package.
Typical Application
Block Diagram
VOUT
95mV
Reference
L
V IN
+
A1
-
V OUT
2.2 μH
10uF
A2
+
Rc
20uF
VIN
FB
VOUT
+
Σ
PAM2805
1uF
PWM
Logic
Cc
SW
BLK
SW
VIN
Comparator
FB
GND
BLK
Dimming
and
Blinking
Logic
Rs
Ramp
Generator
1.0MHz
Oscillator
PGND
ILED=95mV/Rs
Power Analog Microelectronics, Inc
www.poweranalog.com
11/2011 Rev1.0
1
PAM2805
3-Modes/3W WLED Driver with 1 or 2 Cell Battery
Pin Configuration& Marking Information
Top View
SOT23-6
VIN 1
GND 2
BLK 3
6
X: Internal Code
Y: Year
W: Weekly
SW
5 VOUT
4 FB
Pin Number
Name
Function
1
VIN
2
GND
3
BLK
Connect A 1uF CAP for Blinking
4
FB
Feedback
5
VOUT
6
SW
Input Voltage
Power Ground
Output Voltage
Connected to an internal NMOS switc h
Absolute Maximum Ratings
These are stress ratings only and functional operation is not implied . Exposure to absolute
maximum ratings for prolonged time periods may affect device reliability . All voltages are with
respect to ground .
Storage Temperature Range......... –65 
C to 150 
C
Lead Temperature (Soldering, 5 sec) ...........300 
C
Supply Voltage...............................................6V
Output Voltage...............................................6V
Recommended Operating Conditions
Junction Temperature...............- 40
C to 125
C
Operating Temperature Range .......-40 
C to 85 
C
Thermal Information
Param eter
Thermal Resistance
(Junction to Case)
Thermal Resistance
(J unction to Ambient)
Internal Power Dissipation
@TA=25℃
Package
Sym bol
Maximum
SOT23-6
θJ C
130
Unit
℃/W
SOT23-6
θJ A
250
SOT23-6
PD
400
mW
Power Analog Microelectronics, Inc
www.poweranalog.com
11/2011 Rev1.0
2
PAM2805
3-Modes/3W WLED Driver with 1 or 2 Cell Battery
Electrical Characteristic
TA =25 ℃ , L=2.2uH, CΙΝ =10uF, C OUT=10uF, C BLK=1uF, V F =3.4V, unless
otherwise noted.
Parameter
Symbol
Conditions
Min
Input Voltage Range
V IN
0.9
Feedback Voltage
V FB
90
VIN: 0V→3V
Typ
Max
V F-0.2
(note 1)
95
100
Unit
V
mV
Start-up Voltage
V START
Hold Voltage
VHO LD
Oscillator Frequenc y
FO SC
Over Temperature Shutdown
OTS
150
℃
Over Temperature Hysteresis
OTH
30
℃
Maximum O utput Current
Range
IO(M AX)
Quiescent Current
Switch on Resis tance
IQ
ILED =200mA
VIN: 3V→0V
ILED :750mA→100mA
0.85
V IN =2.4V
ILIM
VO=3.4V
Current Limit
Over Voltage Protection(VOUT)
V OVP
Blinking Frequency
FBL K
0.7
V
1.0
1.15
3
2
A
4.5
7
mA
Ω
0.1
CBL K=1uF
MHz
mA
1
Device Switching at 1MHz
VO=3.4V
V
750
ILED =0mA, V O=3.4V,
RDS ON
0.9
8.5
V
10
Hz
Note1: V F --- LED Forward Voltage
Power Analog Microelectronics, Inc
www.poweranalog.com
11/2011 Rev1.0
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PAM2805
3-Modes/3W WLED Driver with 1 or 2 Cell Battery
Typical Performance Characteristics
TA =25 ℃ , L=2.2uH , C ΙΝ =10uF, C ΟUT =10uF, C BLK=1uF, unless otherwise noted.
1. LED Power Efficiency vs Input Voltage
2. LED Current vs Input Voltage
100
800
90
700
80
ILED=750mA( 100% brightnes s )
600
70
60
500
50
400
40
ILED=350mA( 100% brightnes s )
300
30
ILED=750mA(25% brightness )
200
20
ILED=350mA
ILED=750mA
10
100
ILED=350 mA(25% brightnes s )
0
0
3.1
2.8
2.5
2.2
1.9
1.6
1.3
1.0
0.7
3.1
2.8
2.5
2.2
1. 9
1.6
1.3
1.0
0. 7
Input Volt age(V)
Input Voltage(V)
3. DC Input Current vs Input Voltage
4. Feedback Voltage vs Input Voltage
2500
ILED=350mA( 100% brightness)
100
90
2000
ILED=750mA(100% br ightnes s)
80
ILED=750mA( 100% brightness)
70
1500
60
50
1000
40
ILED=350mA (25% brightnes s)
30
500
20
ILED=350mA(100% brightnes s)
ILED=750 mA( 25% br ightness )
10
0
3.4
3.1
2.8
2. 5
2.2
1.9
1.6
1.3
1. 0
0
3. 4
0.7
Input Volt age(V)
3.1
2.8
2. 5
2.2
1.9
1.6
1.3
1.0
0.7
Input Voltage(V)
Power Analog Microelectronics, Inc
www.poweranalog.com
11/2011 Rev1.0
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PAM2805
3-Modes/3W WLED Driver with 1 or 2 Cell Battery
Typical Performance Characteristics
TA =25 ℃ , L=2.2uH , C ΙΝ =10uF, C ΟUT =10uF, C BLK=1uF, unless otherwise noted.
5. 3 Modes Change
6. Start-Up Waveform
VIN
VIN
ILED
VOUT
SW
IL
7. Overvoltage Protection
8. Switching Waveform
VOUT
VOUT
IL
SW
IL
Power Analog Microelectronics, Inc
www.poweranalog.com
11/2011 Rev1.0
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PAM2805
3-Modes/3W WLED Driver with 1 or 2 Cell Battery
Application Information
Inductor Selection
selection is shown as follows:
The PAM2805 can use small value inductors due
to its switching frequency of 1 MHz. The value of
inductor will focus in the range of 2.2uH to 4.7uH
for most PAM2805 applications. In typical high
current white LED applications, it is
recommended to use a 4.7uH inductor. The
inductor should have low DCR (DC resistance) to
2
minimize the I R power loss, and it requires a
current rating of 2A to handle the peak inductor
current without saturating.
Rs(Ohm)=95mV/I LED(mA) at VIN=3V.
Typically, for 1W(330mA) and 3W(750mA) LED
light applications, the Rs are 0.288ohm and
0.127Ohm respectively.
3 Modes Cycling
T h e PA M 2 8 0 5 h a s t h r e e m o d e s : 1 0 0 %
brightness, 25% brightness and blinking(typical
8.5Hz).
Capacitor Selection
The mode change is triggered by power on/off
actions and cycles in the following sequence:
bright, dimming, blinking and back to bright
mode.
An input capacitor is required to reduce the input
ripple and noise for proper operation of the
PAM2805. For good input decoupling, Low ESR
(equivalent series resistance) capacitors should
be used at the input. At least 2.2uF input
capacitor is recommended for most applications.
The PAM2805 will reset to the bright mode after
being power off for more than 5 seconds.
Low Voltage Startup and Soft Start
A minimum output capacitor value of 6.8uF is
recommended under normal operating
conditions, while a 10uF-22uF capacitor may be
required for higher power LED current. A
r e a s on a b l e v a l u e o f t h e o u tp u t c a p ac i t o r
depends on the LED current. The ESR of the
output capacitor is the important parameter to
determine the output voltage ripple of the
converter, so low ESR capacitors should be used
at the output to reduce the output voltage ripple.
The small size of ceramic capacitors is an
excellent choice for PAM2805 applications. The
X5R and X7R types are preferred because they
maintain capacitance over wide voltage and
temperature ranges.
The PAM2805 has a build-in low voltage startup
circuit for the best battery life solution. It can
start up at 0.9V VIN typically when the preset
LED current is 200mA.
The soft-start function is made by clamping the
output voltage of error amplifier with another
voltage source which increases slowly from zero
t o ne a r V IN du r i n g th e s of t- s ta r t p e r i o d .
Therefore, the duty cycle of the PWM will be
increased from zero to maximum in this
period. The charging time of the inductor will be
limited by the smaller duty so that the inrush
current can be reduced to an acceptable
value.`
Diode Selection
Over Voltage Protection
It's indispensable to use a Schottky diode rated
at 2A with the PAM2805. Using a Schottky diode
with a lower forward voltage drop is better to
improve the power LED efficiency, and its voltage
rating should be greater than the output voltage.
SS22 is recommended Schottky diode for
rectifier.
The output voltage of PAM2805 is monitored by
Over Voltage Protection circuit. Once VOUT
goes over VOVP , typically 4.5V, the power NMOS
is turned off and SW pin stops switching.
Then, the VOUT is clamped to around V OVP.
LED Current Setting
The LED current is set by the single external Rs
resistor connected to the FB pin as shown in the
typical application circuit on page 1. The typical
FB reference is internally regulated to 95mV. The
LED current is 95mV/R1. It's recommended to
use a 1% or better precision resistor for the
better LED current accuracy. The formula for Rs
Power Analog Microelectronics, Inc
www.poweranalog.com
11/2011 Rev1.0
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PAM2805
3-Modes/3W WLED Driver with 1 or 2 Cell Battery
Application Information
Over Current Protection
The inductor current during charging period is
detected by a current sensing circuit. When the
value is larger than current limiting I LIM , the power
NMOS is turned off so that the inductor will be
forced to leave charging stage and enter
discharging stage. Therefore, the inductor
peak current will not exceed I LIM , whose minimum
value is 2A.
PCB Layout Guidelines
As for all switching power supplies, the layout
and components placement of the PAM2805 is
an important step in the design; especially at
high peak currents and high switching
frequencies.
The input capacitor and output capacitor should
be placed respectively as close as possible to
the input pin and output pin of the IC; the inductor
and schottky diode should be placed as close as
possible to the switch pin by using wide and short
traces for the main current path; the current
sense resistor should be placed as close as
possible between the ground pin and feedback
pin.
Power Analog Microelectronics, Inc
www.poweranalog.com
11/2011 Rev1.0
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PAM2805
3-Modes/3W WLED Driver with 1 or 2 Cell Battery
Ordering Information
PAM2805 X X X X
Number of Pins: F(6)
Package Type: A
Part Number
Marking
P ackage Type
Standar d Package
PAM2805AF
ECXYW
SOT23-6
3,000Units/Tape&Reel
Power Analog Microelectronics, Inc
www.poweranalog.com
11/2011 Rev1.0
8
PAM2805
3-Modes/3W WLED Driver with 1 or 2 Cell Battery
Outline Dimensions
θ
L REF.
REF.
A
A1
A2
c
D
E
E1
L
L1
θ
b
e
e1
L1 (REF.)
Millimeter
Min
Max
1.35
0.04
0.15
0.70
1.2
0.12REF.
2.70
3.10
2.60
3.00
1.40
1.80
0.45REF.
0.60REF.
0º
10º
0.30
0.50
0.95REF.
1.90REF.
Power Analog Microelectronics, Inc
www.poweranalog.com
11/2011 Rev1.0
9