HDSP2000LP Datasheet, PDF (6/7 Pages) Infineon Technologies AG – 0.150 4-Character 5 x 7 Dot Matrix Serial Input Alphanumeric Display

Thermal Considerations
The small alphanumeric displays are hybrid LED and CMOS
assemblies that are designed for reliable operation in commer-
cial, industrial, and military environments. Optimum reliability
and optical performance will result when the junction tempera-
ture of the LEDs and CMOS ICs are kept as low as possible.
Thermal Modeling
HDSP200XLP displays consist of two driver ICs and four 5 x 7
LED matrixes. A thermal model of the display is shown in Fig-
ure 5. It illustrates that the junction temperature of the semi-
conductor = junction self heating + the case temperature rise +
the ambient temperature. Equation 1 shows this relationship.
Figure 5. Thermal model
LED _T1
R_θ1
IC _T2
R_θ2
LED _T1
R_θ1
LED _T1
R_θ1
IC _T2
R_θ2
LED _T1
R_θ1
LED Power IC Power LED Power LED Power IC Power LED Power
R_θCA
See Equation 1 below.
The junction rise within the LED is the product of the thermal
impedance of an individual LED (37°C/W, DF=20%, F=200 Hz),
times the forward voltage, V_F(LED), and forward current I_F(LED),
of 13–14.5 mA. This rise averages T_J(LED)=1°C. The table below
shows the V_F(LED) for the respective displays.
Model Number
HDSP2000LP
HDSP2001/2/3LP
Min.
1.6
1.9
VF
Typ.
1.7
2.2
Max.
2.0
3.0
The junction rise within the LED driver IC is the combination of
the power dissipated by the IC quiescent current and the 28
row driver current sinks. The IC junction rise is given in
Equation 2.
A thermal resistance of 28°C/W results in a typical junction
rise of 6°C.
For ease of calculations the maximum allowable electrical oper-
ating condition is dependent upon the aggregate thermal resis-
tance of the LED matrixes and the two driver ICs. All of the
thermal management calculations are based upon the parallel
combination of these two networks which is 15°C/W. Maxi-
mum allowable power dissipation is given in Equation 3.
Equation 3.
P_DISPLAY
=
T_{----J---(--M----A----X---)---–-----}T_---A--
R_θJC + R_θCA
P_DISPLAY = 5V_COL I_COL (n ⁄ 35) DF + V_CC I_CC
For further reference see Figures 2, 7, 8, 9, 10 and 11.
Key to equation symbols
DF
I_CC
I_COL
n
P_CASE
P_COL
P_DISPLAY
P_LED
R_θCA
R_θJC
T_A
T_J(IC)
T_J(LED)
T_J(MAX)
V_CC
V_COL
V_F(LED)
Z_θJC
Duty factor
Quiescent IC current
Column current
Number of LEDs on in a 5 x 7 array
Package power dissipation excluding LED
under consideration
Power dissipation of a column
Power dissipation of the display
Power dissipation of a LED
Thermal resistance case to ambient
Thermal resistance junction to case
Ambient temperature
Junction temperature of an IC
Junction temperature of a LED
Maximum junction temperature
IC voltage
Column voltage
Forward voltage of LED
Thermal impedance junction to case
Optical Considerations
The light output of the LEDs is inversely related to the LED
diode’s junction temperature as shown in Figure 6. For opti-
mum light output, keep the thermal resistance of the socket or
PC board as low as possible.
See Equation 2 below.
Equation 1.
T_J(LED) = P_LED Z _{θJ C} + P_CASE (R_θJC + R_θCA)+ T_A
T_J(LED) = [(I_COL ⁄ 28)V_{F (LED)} Z_θJC ] + [(n ⁄ 35)I_COL DF (5V_COL) + V_CC I_CC] ⋅ [R_θJC + R_θCA] + T_A
Equation 2.
T_J(IC) = P_COL(R_θJC + R_θCA) + T_A
T_J(IC) = [5(V_COL – V_F(LED)) ⋅ (I_COL ⁄ 2) ⋅ (n ⁄ 35)DF + V_CC ⋅ I_CC] ⋅ [R_θJC + R_θCA] + T_A
 2000 Infineon Technologies Corp. • Optoelectronics Division • San Jose, CA
www.infineon.com/opto • 1-888-Infineon (1-888-463-4636)
OSRAM Opto Semiconductors GmbH & Co. OHG • Regensburg, Germany
www.osram-os.com • [phone]
6
HDSP200LP/1LP/2LP/3LP
April 4, 2000-11