PAM2804 [PAM]
1A Step-Down Constant Current, High Efficiency LED Driver; 1A降压型恒流，高效率LED驱动器
| 型号： | PAM2804 |
| 厂家： | 
POWER ANALOG MICOELECTRONICS |
| 描述： | 1A Step-Down Constant Current, High Efficiency LED Driver |
| 文件： | 总11页 (文件大小：213K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
PAM2804
1A Step-Down Constant Current, High Efficiency LED Driver
Features
General Description
The PAM2804 is a step-down constant current
n Efficiency up to 93%
LED driver. When the input voltage down to lower
than LED forward voltage, then PAM2804 run into
LDO mode.
n 180μA(TYP.) Quiescent Current
n Output Current: Up to 1A
n Internal Synchronous Rectifier
n 1.5MHz Switching Frequency
n Soft Start
n Under-Voltage Lockout
n Short LED Protection
n Open LED Protection
n Thermal Shutdown
The PAM2804 supports a range of input voltages
from 2.5V to 6.0V, allowing the use of a single
Li+/Li-polymer cell, 3AA or 4AA cell, USB, and
other standard power sources.
The FB voltage is only 0.1V to achieve high
efficiency.
n 5-pin Small SOT23-5 Packages
n Pb-Free Package
PAM2804 employ internal power switch and
synchronous rectifier to minimize external part
count and realize high efficiency.
Applications
n 3AA or 4AA Batteries Powered Flashlight
n 1 Cell Li-Ion Battery Powered Flashlight
During shutdown, the input is disconnected from
the output and the shutdown current is less than
1μA. Other key features include under-voltage
lockout to prevent deep battery discharge of the
Li+ battery.
.
Typical Application
1 Cell Li-Ion Battery
3AA or 4AA Batteries
VIN
L
4.7µH
VIN
SW
1~5W
WLED
CIN
10µF
Co
10µF
GND
FB
Rs
EN
ILED =0.1/Rs
Power Analog Microelectronics, Inc
www.poweranalog.com
10/2010 Rev1.0
1
PAM2804
1A Step-Down Constant Current, High Efficiency LED Driver
Block Diagram
+
IAMP
-
VIN
1.5M
OSC
SLOPE
COMP
FB
FREQ
SHIFT
OSC
S Q
MAIN
SWITCH( PCH)
SWITCHING
LOGIC
AND
BLANKING
CIRCUIT
R Q
RS LATCH
ANTI-
-
+
SW
SHOOT-
EA
THRU
VIN
SYNCHRONOUS
COMP
RECTIFIER(NCH)
0.6VREF
EN
+
IRCMP
-
SHUTDOWN
GND
Pin Configuration & Marking Information
Top View
SOT23-5
EE: Product Code
FB
1
2
3
EN
5
4
of PAM2804
X: Internal Code
Y: Year
GND
W: Week
SW
VIN
Pin Description
Name
VIN
Function
Chip main power supply pin
Ground
GND
Enable control input. Force this pin voltage above 1.5V, enables the chip, and below
0.3V shuts down the device.
EN
FB
Feedback voltage to internal error amplifier, the threshold voltage is 0.1V.
The drains of the internal main and synchronous power MOSFET.
SW
Power Analog Microelectronics, Inc
www.poweranalog.com
10/2010 Rev1.0
2
PAM2804
1A Step-Down Constant Current, High Efficiency LED Driver
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.
Input Voltage..................................-0.3V to 6.5V Junction Temperature................................150°C
EN, FB Pin Voltage...........................-0.3V to VIN Storage Temperature Range........-65°C to 150°C
SW Pi n Voltage.....................-0.3V to (VIN+0.3V)
Soldering Temperature......................300°C,5sec
Recommended Operating Conditions
Supply Voltage................................2.5V to 6.0V
Operation Temperature Range.........-40°C to 85°C
Junction Temperature Range........-40 °C to 125 °C
Thermal Information
Parameter
Package
Symbol
Maximum
Unit
°C/W
mW
Thermal Resistance
(Junction to Case)
SOT23-5Note
θJC
130
Thermal Resistance
(Junction to Ambient)
SOT23-5
SOT23-5
θJA
250
400
Internal Power Dissipation
PD
Note:
The maximun output current for SOT23-5 package is limited by internal power dissipation capacity as
described in Application Information herein after.
Power Analog Microelectronics, Inc
www.poweranalog.com
10/2010 Rev1.0
3
PAM2804
1A Step-Down Constant Current, High Efficiency LED Driver
Electrical Characteristic
TA =25°C, VIN =4.2V, Real WLED load, CIN =10µF, CO =10µF, L=4.7µH, unless otherwise noted.
PARAMETER
Input Voltage Range
SYMBOL
Test Conditions
MIN
2.5
TYP
MAX
6.0
UNITS
V
V
IN
Regulated Feedback Voltage
Peak Inductor Current
Quiescent Current
VFB
IPK
0.095
0.1
1.5
0.105
V
VIN=5V
A
IQ
No load
180
µA
µA
MHz
Ω
Shutdown Current
ISD
fOSC
VEN = 0V
VO = 100%
1
1.8
0.45
0.5
1
Oscillator Frequency
1.2
1.5
1.5
0.3
P MOSFET
N MOSFET
Drain-Source On-State Resistance
RDS(ON)
IDS=100mA
0.35
±0.01
93
Ω
SW Leakage Current
High Efficiency
ILSW
η
µA
%
EN Threshold High
EN Threshold Low
EN Leakage Current
Over Temperature Protection
OTP Hysteresis
VEH
VEL
V
0.3
V
IEN
±0.01
150
30
µA
°C
°C
OTP
OTH
Power Analog Microelectronics, Inc
www.poweranalog.com
10/2010 Rev1.0
4
PAM2804
1A Step-Down Constant Current, High Efficiency LED Driver
Typical Performance Characteristics
TA =25°C, CIN =10μF, CO =10μF, L=4.7μH, unless otherwise noted.
Eifficiency VS Input Voltage
Output Current VS Input Voltage
96%
94%
92%
90%
88%
86%
84%
82%
350
300
250
200
150
100
50
330m A
750m A
1A
Rcs=0.3ohm
0
3
3.5
4
4.5
5
5.5
6
2.5
3
3.5
4
4.5
Vin(V)
5
5.5
6
Input Voltage (V)
Output Current VS Input Voltage
Output Current VS Input Voltage
1200
1000
800
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
600
400
200
0
Rcs=0.135ohm
Rcs=0.1ohm
2.5
3
3.5
4
4.5
Vin(V)
5
5.5
6
3
3.5
4
4.5
Input Voltage (V)
Rdson VS Input Voltage
5
5.5
6
Rdson VS Temperature
Vin=3.6V
0.6
0.5
0.4
0.3
0.2
0.1
0
0.4
0.35
0.3
0.25
0.2
Vin=4.2V
0.15
0.1
Vin=3.6V
Vin=2.7V
2
3
4
5
6
20
70
120
Input Voltage
Temperature(℃)
Power Analog Microelectronics, Inc
www.poweranalog.com
10/2010 Rev1.0
5
PAM2804
1A Step-Down Constant Current, High Efficiency LED Driver
Typical Performance Characteristics
TA =25 OC, CIN =10μF, CO =10μF, L=4.7μH, unless otherwise noted.
Quiescent Current Vs Input Voltage
Start up with Enable
200
180
160
140
120
100
80
60
40
20
0
3
3.5
4
4.5
Input Voltage (V)
switch on switch off
5
5.5
6
Power Analog Microelectronics, Inc
www.poweranalog.com
10/2010 Rev1.0
6
PAM2804
1A Step-Down Constant Current, High Efficiency LED Driver
Application Information
The basic PAM2804 application circuit is shown
in Page 1. External component selection is
determined by the load requirement, selecting L
first and then Cin and Cout.
temperature should be maintained below 125°C.
The power dissipation is defined as:
VORDSONH+ V -V
R
(
)
DSONL + tSWFSIO +IQ
IN
O
2
PD=IO
V
)
IN
(
V
IN
Inductor Selection
IQ is the step-down converter quiescent current.
The term tsw is used to estimate the full load
step-down converter switching losses.
For most applications, the value of the inductor
will fall in the range of 1µH to 4.7µH. Its value is
chosen based on the desired ripple current.
Large value inductors lower ripple current and
small value inductors result in higher ripple
currents. Higher VIN or Vout also increases the
ripple current as shown in equation 1. A
reasonable starting point for setting ripple
current is △IL = 400mA (40% of 1A).
1
V
OUT
(1)
DIL =
V
OUT 1-
f
L
V
IN
( )( )
The DC current rating of the inductor should be
at least equal to the maximum load current plus
half the ripple current to prevent core saturation.
Thus, a 1.4A rated inductor should be enough for
most applications (1A + 400mA). For better
efficiency, choose a low DC-resistance inductor.
Using Ceramic Input and Output Capacitors
Higher values, lower cost ceramic capacitors are
now becoming available in smaller case sizes.
Their high ripple current, high voltage rating and
low ESR make them ideal for switching regulator
applications. Using ceramic capacitors can
achieve very low output ripple and small circuit
size.
When choosing the input and output ceramic
capacitors, choose the X5R or X7R dielectric
formulations. These dielectrics have the best
temperature and voltage characteristics of all
the ceramics for a given value and size.
Thermal consideration
Thermal protection limits power dissipation in
the PAM2804. When the junction temperature
exceeds 150°C, the OTP (Over Temperature
Protection) starts the thermal shutdown and
turns the pass transistor off. The pass transistor
r e s u m e s o p e r a t i o n a f t e r t h e j u n c t i o n
temperature drops below 120°C.
Fo r c o nt i n uo u s op e ra ti o n, th e j un c t io n
Power Analog Microelectronics, Inc
www.poweranalog.com
10/2010 Rev1.0
7
PAM2804
1A Step-Down Constant Current, High Efficiency LED Driver
Application Information
For the condition where the step-down converter
is in dropout at 100% duty cycle, the total device
dissipation reduces to:
As the input voltage approaches the LED forward
voltage, the PAM2804 turns the P-channel
transistor continuously on. In this mode the
Voltage drop on LED is equal to the input voltage
minus the voltage drop across the P - channel
transistor, Inductor and current resistor:
2
P =IO RDSONH+IQV
D
IN
Since RDS(ON), quiescent current, and switching
losses all vary with input voltage, the total losses
should be investigated over the complete input
voltage range. The maximum power dissipation
depends on the thermal resistance of IC
package, PCB layout, the rate of surrounding
airflow and temperature difference between
junction and ambient. The maximum power
dissipation can be calculated by the following
formula:
VLEDDROP = VIN – ILED (Rdson + RL+ RS)
where Rdson = P-channel switch ON resistance,
ILED = LED current, RL = Inductor DC resistance,
RS = Inductor DC resistance.
Thermal Shutdown
T
J(MAX) -TA
When the die temperature exceeds 150°C, a
reset occurs and the reset remains until the
temperature decrease to 120°C, at which time
the circuit can be restarted.
PD=
θJA
Where TJ(max) is the maximum allowable
junction temperature 125°C.TA is the ambient
temperature and θJA is the thermal resistance
from the junction to the ambient. Based on the
standard JEDEC for a two layers thermal test
board, the thermal resistance θJA of SOT23-5
package is 250°C/W. The maximum power
dissipation at TA = 25°C can be calculated by
following formula:
PD=(125°C-25°C)/250°C/W=0.4W
Setting the Output Current
The internal feedback(FB) voltage is 0.1V
(Typical). The output current is calculated as
below:
ILED=0.1/Rs
The output Current is given by the following
table.
Rs(Ω)
0.286
0.143
0.1
ILED(mA)
350
700
1000
100% Duty Cycle Operation
Power Analog Microelectronics, Inc
www.poweranalog.com
10/2010 Rev1.0
8
PAM2804
1A Step-Down Constant Current, High Efficiency LED Driver
Application Information
PCB Layout Check List
When laying out the printed circuit board, the following checklist should be used to ensure proper operation of
the PAM2804. These items are also illustrated graphically in Figure 1. Check the following in your layout:
1. The power traces, consisting of the GND trace, the SW trace and the VIN trace should be kept short, direct
and wide.
2. Does the VFB pin connect directly to the current sense resistor? The current sense resistor to GND trace
should be kept short, direct and wide.
3. Does the (+) plate of CIN connect to VIN as closely as possible? This capacitor provides the AC current to
the internal power MOSFETs.
4. Keep the switching node, SW, away from the sensitive VFB node.
5. Keep the (–) plates of CIN and COUT as close as possible.
Power Analog Microelectronics, Inc
www.poweranalog.com
10/2010 Rev1.0
9
PAM2804
1A Step-Down Constant Current, High Efficiency LED Driver
Ordering Information
PAM 2804 X X X XXX
FB Voltage
Number of Pins
Package Type
Pin Configuration
Pin Configuration
A Type
Package Type
Number of Pins
FB Voltage
A: SOT-23
B: 5
010: 0.1V
1. EN
2. GND
3. SW
4. VIN
5. FB
Part Number
Marking
Package Type
Standard Package
PAM2804AAB010
Refer to P2
SOT-23-5
3,000Units/Tape&Reel
Power Analog Microelectronics, Inc
www.poweranalog.com
10/2010 Rev1.0
10
PAM2804
1A Step-Down Constant Current, High Efficiency LED Driver
Outline Dimensions
SOT23-5
D
e1
θ
L REF.
L1 (REF.)
e
b
Millimeter
REF.
Min
Max
A
A1
A2
c
1.10MAX
0
0.10
1
0.70
0.12REF.
D
2.70
2.60
1.40
0.45REF.
0.60REF.
0º
0.30
3.10
3.00
1.80
E
E1
L
L1
θ
b
10º
0.50
e
e1
0.95REF.
1.90REF.
Power Analog Microelectronics, Inc
www.poweranalog.com
10/2010 Rev1.0
11
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