PAM2804
Document number: DS36403 Rev. 3 - 2
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PAM2804
1A STEP-DOWN CONSTANT CURRENT, HIGH EFFICIENCY LED DRIVER
Description
The PAM2804 is a step-down constant current LED driver. When the
input voltage is down to lower than LED forward voltage, then
PAM2804 goes 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 employs 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
undervoltage 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
Undervoltage 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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PAM2804
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
Document number: DS36403 Rev. 3 - 2
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PAM2804
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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PAM2804
Application Information
PWM Dimming
The PAM2804 can be used to dim LED current dimming by driving the EN pin via PWM waveform. The SW pin current is then effectively
switched on and off causing the LED current to turn on and off. The recommended PWM frequency is 500Hz (see Figure on page 5 for details).
Inductor Selection
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.
For most applications, the value of the inductor will fall within 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).
V
V
1
V
Lf1
IIN
OUT
OUT
L
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 (Overtemperature
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:
VI
IF
t
VRVVRV
IP INQ
OS
SW
IN
L)ON(DSOINH)ON(DSO
2
OD
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(DS
2
OD
PAM2804
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PAM2804
Application Information (cont.)
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:
JA
A)MAX(J
DTT
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:
WWCCC
PD4.0/250/25125
Setting the Output Current
The internal feedback (FB) voltage is 0.1V (Typical). The output current is calculated as below:
R
/1.0
ISLED
The output Current is given by the following table.
RS(Ω)
ILED(mA)
0.286
350
0.143
700
0.1
1,000
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:
RRR
ILED
VV 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
Ordering Information
PAM2804 X X X xxx
Pin Configuration B: 5
A Type:1. EN
2. GND
3. SW
4. VIN
5. FB
A: TSOT25
Package Type Number of Pins FB Voltage
010: 0.1V
Part Number
Marking
Package Type
Standard Package
PAM2804AAB010
Refer to Marking
Information Below
TSOT25
3,000 Units/Tape & Reel
Marking Information
Top View
TSOT25
PAM2804
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PAM2804
Package Outline Dimensions
TSOT25
D
E1
E1/2
e1
E
E/2
e
A
A2
A1
Seating Plane
0
L2
L
Gauge Plane
01(4x)
01(4x)
c
b
Seating Plane
TSOT25
Dim
Min
Max
Typ
A
-
1.00
-
A1
0.01
0.10
-
A2
0.84
0.90
-
b
0.30
0.45
-
c
0.12
0.20
-
D
-
-
2.90
E
-
-
2.80
E1
-
-
1.60
e
0.95 BSC
e1
1.90 BSC
L
0.30
0.50
L2
0.25 BSC
θ
0°
8°
4°
θ1
4°
12°
-
All Dimensions in mm
Suggested Pad Layout
TSOT25
Y1
C
X
Y
Dimensions
Value (in mm)
C
0.950
X
0.700
Y
1.000
Y1
3.199
PAM2804
Document number: DS36403 Rev. 3 - 2
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PAM2804
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