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PAM2861
1A LED DRIVER WITH INTERNAL SWITCH
Description
The PAM2861 is a continuous mode inductive step-down converter,
designed for driving single or multiple series connected LEDs
efficiently from a voltage source higher than the LED voltage. The
device operates from an input supply between 6V and 40V and
provides an externally adjustable output current of up to 1A.
Depending upon supply voltage and external components, this can
provide up to 30 watts of output power.
The PAM2861 includes the output switch and a high-side output
current sensing circuit, which uses an external resistor to set the
nominal average output current.
Output current can be adjusted below the set value, by applying an
external control signal to the VSET pin.
The VSET pin will accept either a DC voltage or a PWM waveform.
The soft-start time can be increased using an external capacitor from
the VSET pin to ground. Applying a voltage of 0.2V or lower to the
VSET pin turns the output off and switches the device into a low
current standby state.
Features
Simple Low Parts Count
Internal 40V NDMOS Switch
1A Output Current
Single Pin On/Off and Brightness Control Using DC Voltage or
PWM
Soft-Start
High Efficiency (up to 97%)
Wide Input Voltage Range: 6V to 40V
Output Shutdown
Open LED Protection
Short LED Protection
Up to 1MHz Switching Frequency
Inherent Open-Circuit LED Protection
Typical 5% Output Current Accuracy
Pb-free TSOT25 and SOT89-5 Packages
Pin Assignments
Top View
TSOT25
Applications
Low voltage halogen replacement LEDs
Low voltage industrial lighting
LED back-side lighting
Illuminated signs
PAM2861
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Typical Applications Circuit
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PAM2861
Pin Descriptions
Pin
Number
1 LX
2 GND
3 VSET
4 ISENSE
5 VIN
Pin
Name
Function
Drain of NDMOS switch.
Ground (0V)
• Multi-function On/Off and brightness control pin:
• Leave floating for normal operation.
• Drive to voltage below 0.2V to turn off output current
• Drive with DC voltage (0.3V < VSET< 2.5V) to adjust output current from 12% to 100% of I
• Drive with PWM signal from open-collector or open-drain transistor, to adjust output current. Adjustment range
1% to 100% of I
• Connect a capacitor from this pin to ground to increase soft-start time.
(Default soft-start time = 0.1ms. Additional soft-start time is approx.1.5ms/1nF)
Connect resistor RS from this pin to VIN to define nominal average output current
nom = 0.1/Rs
I
OUT
Input voltage (6V to 40V). Decouple to ground with 10F or higher X7R ceramic capacitor close to device.
nom for f < 500Hz
OUT
OUT
nom
PAM2861
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Functional Block Diagram
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PAM2861
Absolute Maximum Ratings (@T
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 Voltage Range -0.3 to +40
LX, I
VSET Pin Voltage -0.3 to +6.0
Maximum Junction Temperature 170
Storage Temperature -65 to +170
Soldering Temperature 300, 5sec
SENSE
Pin Voltage
Recommended Operating Conditions (@T
Parameter Rating Unit
Input Voltage Range 6 to 40 V
Ambient Temperature Range -40 to +85 °C
Junction Temperature Range -40 to +150
PAM2861
Document number: DSxxxxx Rev. 1 - 1
= +25°C, unless otherwise specified.)
A
-0.3 to +40
= +25°C, unless otherwise specified.)
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V
°C
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PAM2861
Thermal Information
Parameter Package Symbol Max Unit
Thermal Resistance (Junction to Ambient)
Thermal Resistance (Junction to Case)
TSOT25
SOT89-5 160
TSOT25
SOT89-5 45
JA
JC
Electrical Characteristics (@T
= +25°C, VIN = 16V, unless otherwise specified.)
A
Parameter Symbol Test Conditions Min Typ Max Units
Input Voltage
Output Current
Shutdown Current
Quiescent Current without Switching
Mean Current Sense Threshold Voltage
Sense Threshold Hysteresis
ISENSE Pin Input Current
VSET Range on VSET Pin
DC Voltage on VSET Pin to Enable
DC Voltage on VSET Pin to Disable
LX Switch On Resistance
LX Switch Leakage Current
Soft Start Time
Operating Frequency
Recommended Minimum Switch ON Time
Recommended Maximum Switch Frequency
V
IN
I
LED
I
SD
I
VSET Pin Floating, VIN = 16V
Q
V
SENSE
V
SENSE_HYS
I
SENSE
V
EN
V
EN(ON)
V
EN(OFF)
@ILX = 100mA
R
LX
I
LX(LEAK)
VIN = 16V, CEN = 1nF
T
SS
F
LX
T
ON_REC
F
LX(MAX)
= 0.3
R
S
RS = 0.1
VSET Pin Grouded 20 40 µA
Measured on I
Respect to V
±13 %
V
SENSE
IN
= VIN -0.1
For DC Dimming 0.3 2.5 V
VEN Rising
VEN Falling
5 µA
= 16V, VO = 9.6V (3 LEDs)
V
I
L = 47µF, I = 0.25A (I
For 4% Accuracy 500 Ns
1.0 MHz
Max Duty Circle 98 %
Recommended Duty Cycle Range
Internal Comparator Propagation Delay
Over Temperature Protection
Temp Protection Hysteresis
Current Limit
Note: 1. Parameters are not tested at production, but guaranteed by design. V
T
PD
T
OTP_HYS
I
XL(MAX)
D
LX
(Note 1)
T
OTP
25 75 %
45 ns
150 °C
40 °C
Peak Inductor Current 1.5 A
: level A: 95mV to 100mV; level B: 100mV to 105mV.
SENSE
PAM2861
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SENSE
250
130
Pin with
= 1A)
LED
°C/W
6 40 V
333 mA
1 A
0.6 mA
95 100 105 mV
8 µA
0.25 V
0.2 V
0.3
1.5 ms
233 kHz
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Typical Performance Characteristics (@T
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= +25°C, VIN = 16V, unless otherwise specified.)
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PAM2861
PAM2861
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Typical Performance Characteristics (cont.) (@T
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= +25°C, VIN = 16V, unless otherwise specified.)
A
PAM2861
PAM2861
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Typical Performance Characteristics (cont.) (@T
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PAM2861
= +25°C, CIN = 10µF, CO = 10µF, L = 4.7µH, unless otherwise specified.)
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PAM2861
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PAM2861
Application Information
Setting Nominal Average Output Current with External Resistor RS
The nominal average output current in the LED(s) is determined by the value of the external current sense resistor (RS) connected between VIN
and I
I
The table below gives values of nominal average output current for several preferred values of current setting resistor (R
application circuit shown on page 1.
The above values assume that the VSET pin is floating and at a nominal voltage of VREF (1.25V). Note that R
value of sense resistor under these conditions to maintain switch current below the specified maximum value. It is possible to use different
values of R
Capacitor Selection
A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in series with the supply source impedance and
lowers overall efficiency. This capacitor has to supply the relatively high peak current to the coil and smooth the current ripple on the input
supply.
A minimum value of 4.7µF is acceptable if the input source is close to the device, but higher values will improve performance at lower input
voltages, especially when the source impedance is high. The input capacitor should be placed as close as possible to the IC.
For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better dielectric are recommended. Capacitors with
Y5Vdielectric are not suitable for decoupling in this application and should NOT be used.
Inductor Selection
Recommended inductor values for the PAM2861 are in the range 33µH to 100µH. Higher values of inductance are recommended at higher
supply voltages in order to minimize errors due to switching delays, which in increased ripple and lower efficiency. Higher values of inductance
also result in a smaller change in output current over the supply voltage range. The inductor should be mounted as close to the device as
possilbe with low resistance connections to the LX and VIN pins. The chosen coil should have a saturation current higher than the peak output
current and a continuous current rating above the required mean output current.
The inductor value should be chosen to maintain operating duty cycle and switch ‘on’/’off’ times within the specified limits over the supply voltage
and load current range. The following equations can be used as a guide.
LX Switch ‘On’ time
Lx Switch ‘Off’ time
Where: L is the coil inductance; R
peak ripple current (Internally set to 0.25 x I
(0.3 nominal); V
PAM2861
Document number: DSxxxxx Rev. 1 - 1
and is given by:
SENSE
1.0
)NOM(OUT
R
S
(Ω)
R
S
0.1 1000
0.13 760
0.15 667
0.3 333
Nominal Average Output
Current (mA)
if the VSET pin is driven from an external voltage.
S
IL
T
ON
T
OFF
is the diode forward voltage at the required load current
D
(
IVV
IL
(
IVV
is the coil resistance; RS is the current sense resistance I
L
RR
LED
)
RRR
LXLSLEDLEDIN
)
LSLEDDLED
); VIN is the supply voltage; V
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) in the typical
S
= 0.1 is the minimum allowed
S
is the required LED current; I is the coil peak-
LED
is the total LED forward voltage; RLX is the switch resistance
LED
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PAM2861
Application Information (cont.)
Diode Selection
For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode with low reverse leakage at the
maximum operating voltage and temperature. They also provide better efficiency than silicon diodes, due to a combination of lower forward
voltage and reduced recovery time.
It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher than the maximum
output load current. It is very important to consider the reverse leakage of the diode when operating above +85°C. Excess leakage will increase
the power dissipation in the device and if close to the load may create a thermal runaway condition.
The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak voltage on the LX output. If a
silicon diode is used, care should be taken to ensure that the total voltage appearing on the LX pin including supply ripple, d oes not exceed the
specified maximum value.
Ordering Information
Part Number Part Marking Package Type Standard Package
PAM2861ABR EQXYW TSOT25 3000 Units/ Tape&Reel
PAM2861CBR
Marking Information
XXXYW
Top View
TSOT25
P2861
SOT89-5 1000 Units/ Tape&Reel
PAM2861
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Package Outline Dimensions (All dimensions in mm.)
TSOT25
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PAM2861
PAM2861
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Package Outline Dimensions (cont.) (All dimensions in mm.)
SOT89-5
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PAM2861
PAM2861
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PAM2861
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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).
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This document is written in English but may be translated into multiple languages for reference. Onl y the English version of this document is the
final and determinative format released by Diodes Incorporated.
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:
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Copyright © 2013, Diodes Incorporated
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IMPORTANT NOTICE
LIFE SUPPORT
PAM2861
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