PAM2804
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PAM2804
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1A STEP-DOWN CONSTANT CURRENT, HIGH EFFICIENCY LED DRIVER
Description
The PAM2804 is a step-down constant current LED driver. When the
input voltage down to lower than LED forward voltage, then PAM2804
run into LDO mode.
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.
PAM2804 employ internal power switch and synchronous rectifier to
minimize external part count and realize high efficiency.
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.
Features
• Efficiency up to 93%
• 180µA(typ) Quiescent Current
• Output Current: Up to 1A
• Internal Synchronous Rectifier
• 1.5MHz Switching Frequency
• Soft-Start
• Under-Voltage Lockout
• Short LED Protection
• Open LED Protection
• Thermal Shutdown
• 5-Pin Small TSOT25 Packages
• Pb-Free Package
Pin Assignments
Applications
• 3AA or 4AA Batteries Powered Flashlight
• 1 Cell Li-Ion Battery Powered Flashlight
Typical Applications Circuit
ILED = 0.1/RS
Top View
TSOT25
PAM2804
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Pin Description
Pin
Number
Pin
Name Function
1 EN Enable control input. Force this pin voltage above 1.5V, enables the chip, and below 0.3V shuts down the device.
2 GND Ground
3 SW The drains of the internal main and synchronous power MOSFET.
4 VIN Chip main power supply pin.
5 FB Feedback voltage to internal error amplifier, the threshold voltage is 0.1V.
Block Diagram
Absolute Maximum Ratings (@TA = +25°C, unless otherwise specified.)
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.
Parameter Rating Unit
Input Pin Voltage -0.3 to +6.5
V EN, FB Pin Voltage -0.3 to VIN
SW Pin Voltage -0.3 to (VIN +0.3)
Junction Temperature Range 150
°C Storage Temperature Range -65 to +150
Soldering Temperature 300, 5sec
PAM2804
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PAM2804
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Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.)
Parameter Rating Unit
Supply Voltage 2.5 to 6.0
°C Operation Temperature Range -40 to +85
Junction Temperature Range -40 to +125
Thermal Information
Parameter Symbol Package Max Unit
Thermal Resistance (Junction to Case) θJC TSOT25 (Note 1) 130
°C/W
Thermal Resistance (Junction to Ambient) θJA TSOT25 250
Internal Power Dissipation PD TSOT25 400 mW
Note: 1. The maximum output current for TSOT25 package is limited by internal power dissipation capacity as described in Application Information herein after.
Electrical Characteristics
(@TA = +25°C, VIN = 4.2V, Real WLED load, L = 4.7µH, CIN = 10µF, CO = 10µF, unless otherwise specified.)
Parameter Symbol Test Conditions Min Typ Max Units
Input Voltage Range VIN 2.5 6.0 V
Regulated Feedback Voltage VFB 0.095 0.100 0.105 V
Peak Inductor Current IPK VIN = 5V 1.5 A
Quiescent Current IQ No Load 180 µA
Shutdown Current ISD VEN = 0V 1 µA
Oscillator Frequency fOSC VO = 100% 1.2 1.5 1.8 MHz
Drain-Source On-State Resistance RDS(ON) IDS = 100mA
P MOSFET 0.30 0.45 Ω
N MOSFET 0.35 0.50 Ω
SW Leakage Current ILSW ±0.01 1 µA
High Efficiency η 93 %
EN Threshold High VEH 1.5 V
EN Threshold Low VEL 0.3 V
EN Leakage Current IEN ±0.01 µA
Over Temperature Protection OTP 150 °C
OTP Hysteresis OTH 30 °C
PAM2804
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Typical Performance Characteristics (@TA = +25°C, L = 4.7µF, CIN = 10µF, CO = 10µF, unless otherwise specified.)
PAM2804
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Typical Performance Characteristics (cont.) @TA = +25°C, L = 4.7µF, CIN = 10µF, CO = 10µF, unless otherwise specified.)
PAM2804
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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.
Inductor Selection
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 ΔIL = 400mA (40% of 1A).
( )( ) ⎟⎟⎠
⎞
⎜⎜⎝
⎛ −=Δ
V
V1VLf
1I
IN
OUT
OUTL Equation (1)
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 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 resumes operation after the junction temperature
drops below +120°C.
For continuous operation, the junction temperature should be maintained below +125°C. The power dissipation is defined as:
( ) ( )VIIFt
V
RVVRV
IP INQOSSW
IN
L)ON(DSOINH)ON(DSO2OD ++
−+=
IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down converter switching losses.
For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to:
VIRIP INQH)ON(DS2OD +=
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:
θ
−=
JA
A)MAX(J
D
TT
P
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 TSOT25 package is
250°C/W. The maximum power dissipation at TA = +25°C can be calculated by following formula:
( ) W4.0W/C250/C25C125PD =°°−°=
PAM2804
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Application Information
Setting the Output Current
The internal feedback(FB) voltage is 0.1V (Typical). The output current is calculated as below:
R/1.0I SLED =
The output Current is given by the following table.
RS(Ω) ILED(mA)
0.286 350
0.143 700
0.1 1000
As the input voltage approaches the LED forward voltage, the PAM2804 turns the P-Chan nel 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:
( )RRRILEDVV SL)ON(DSINLEDDROP ++−=
where RDS(ON) = P-Channel switch ON resistance, ILED = LED current, RL = Inductor DC Resistance, RS = Inductor DC Resistance.
Thermal Shutdown
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.
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.
PAM2804
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PAM2804
A Product Line of
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Ordering Information
Part Number Marking Package Type Standard Package
PAM2804AAB010 Refer to Marking Information Below TSOT25 3000 Units/Tape&Reel
Marking Information
Top View
TSOT25
PAM2804
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Package Outline Dimensions (All dimensions in mm.)
TSOT25
PAM2804
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IMPORTANT NOTICE
DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
(AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).
Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes
without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the
application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or
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website, harmless against all damages.
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This document is written in English but may be translated into multiple languages for reference. Only the English version of this document is the
final and determinative format released by Diodes Incorporated.
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Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express
written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body, or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the
labeling can be reasonably expected to result in significant injury to the user.
B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the
failure of the life support device or to affect its safety or effectiveness.
Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and
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any use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related
information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and its
representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or
systems.
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