下载
© Semiconductor Components Industries, LLC, 2012
May, 2012 − Rev. 2
1 Publication Order Number:
AND9008/D
AND9008/D
Thermal Considerations for
the ON Semiconductor
Family of Discrete Constant
Current Regulators (CCR) in
DPAK, SMC and SMB
packages for Driving LEDs
Prepared by: Mike Sweador and David Helzer
ON Semiconductor
Introduction:
This application note supplements AND8391/D adding
thermal information for DPAK, SMB and SMC packages
and includes performance data for both FR4 and Thermal
(aluminum backed) MCPCB ( Metal Clad PCB) material.
The ON Semiconductor Constant Current Regulator
(CCR) family of devices offers outstanding regulation for
LEDs and other current based loads, such as battery
charging circuits. The CCR reduces the complexity of
resistor biased designs for sensitive loads, such as LED
strings connected in series. The CCR can also be connected
in parallel for higher load current applications. See
application note AND8349/D for basic circuit
considerations.
The two−terminal CCR requires no external components
to regulate at the specified current. The three−terminal
device allows for current adjustment by using an external
resistor. In the automotive lighting market (see app note
AND8349/D), these devices can be used wherever a
constant current is needed to maintain luminosity under
varying voltage conditions.
The purpose of this paper is to explore the temperature and
power boundaries for devices in the DPAK, SMB and SMC
package operating from typical currents of 50 mA to
350 mA in LED lighting applications. The DPAK adjustable
devices available are rated at 60 mA to 100 mA and 90 mA
to 160 mA. The fixed DPAK and SMC devices are rated at
350 mA. The SMB devices are rated at 50 mA ±10%, 30 mA
±10% and 20 mA ±15% with a higher breakdown voltage of
120 V. See appendix A for device list.
Reference to Data Sheet:
The data sheet describes the devices and defines the
following terms that will be used throughout this note:
Vak = Voltage applied between the Anode and Cathode of
the device.
Ireg−ss = The current through the device supplied to the
LEDs under steady−state operating conditions (device on
≥5 min.)
Ireg−p = The current through the device supplied to the
LEDs under pulse test conditions (≤ 300 msec).
V
R
= Reverse Voltage
P
D
= Device power dissipation, typically in mW.
T
A
= Ambient Temperature in °C
T
J
= Device Junction Temperature in °C
The DPAK adjustable CCR Data Sheet Thermal
Characteristics table lists the thermal performance of each
device as related to the heat spreader area and thickness.
These datasheet tables and curves show thermal
specifications and limits with the device junction
temperature (T
J
) operating at 150°C, the maximum
allowable continuous junction temperature mounted on FR4
PCB material.
Operating at T
J
max
continuously is not recommended for
long term reliability.
http://onsemi.com
APPLICATION NOTE
