SP7121 View Datasheet(PDF) - Exar Corporation
Part Name
Description
MFG CO.
'SP7121' PDF : 10 Pages View PDF
SP7121
2-Channel Adjustable Low Dropout High Side Linear
LED Driver
THERMAL CONSIDERATIONS
The SP7121 does not have over temperature
protection. Special care needs to be taken to
ensure that the driver’s junction temperature
stays below 125°C. The thermal resistance of
the package is 190°C per Watt. Under normal
operation conditions with about 30mA of
current per LED and a voltage drop across the
part of 1V, the part will still only dissipate 0.06
Watts, giving a temperature rise of only
11.4°C.
Example of thermal calculation:
Where P is the total power dissipation, VD is
the voltage drop across the SP7121, IOUT is the
total output current.
Where P is the total power dissipation, θJA is
the thermal resistance of the package per
Watt.
Above example:
1 60
0.06
0.06 190 11.4°
The device will be able to operate up to 85°C
under these conditions.
BOARD LAYOUT AND GROUNDING
Although the SP7121 does not require an input
capacitor for normal operation, a 1nF capacitor
can be used to obtain better overall circuit
performance. To obtain the best performance
from the SP7121, a printed circuit board with
ground plane is required. High quality, low
series resistance ceramic 1nF bypass
capacitors should be used at the Vcc and GND
pins (pins 1 and 2). This capacitor must be
located as close to the pins as possible. The
traces connecting the pins and the capacitor
must be kept short and should be made as
wide as possible.
APPLICATION SCHEMATICS
© 2010 Exar Corporation
8/10
Rev. 2.0.0
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