OSRAM OPTOTRONIC Constant current LED power supplies with 3DIM - Manual (Page 29)

29
3.3.1.5. Application solution 5 – MM3488 solution
The MM3488 (MITSuMI) is a temperature switch IC that
changes the IC output level from “low” to “high” when the
temperature around the IC reaches the detection tempera-
ture. With the hysteresis function (5 °C, 10 °C, 15 °C), the IC
output level returns to “low” when the ambient temperature
drops to the temperature hysteresis selected after detection.
Detection temperature Tset
TH
can be selected in steps of
1.0 °C between 60 and 90 °C with rank expansion (available
as factory-trimmed value), with a detection temperature
accuracy of ±2.0 °C.
The very-small-outline package SSON-4B allows saving
space on the LED module, compensating for the higher
overall number of components with respect to the previous
solutions.
A noise rejection time t
noise
between 250 and 500 µs allows
debouncing the temperature signal, preventing unstable out-
put switching caused by possible noise.
In fi gure 21, a reference schematic is shown. Since the maxi-
mum operating voltage is limited to 5.5 V, a voltage regulator
is needed in order to supply the MM3488 via the LEDset
interface. The simplest solution is to clamp the supply volt-
age with a Zener diode (D
1
). In order to ensure a suffi cient
reverse current to the diode, a proper value of R
1
has to be
selected. A by-pass capacitor (C
1
) between pin 4 and ground
(pin 2) is recommended.
LEDset APPLICATIONS
Figure 21: Thermal protection – MM3488 solution (via output transistor).
D
1
= 5 V1 5 % signal Zener diode (i.e. NXP BZT52H-C5V1)
C
1
= 100 nF 25 V 10 % X7R 0603
Q
1
= NPN signal transistor (BC847)
R
1
= 1K 5 % 0603
R
2
= 10K 5 % 0603
R
3
= 100K 5 % 0603
Since the IC output is only an open drain, a pull-up resistor
is needed.
Example:
Considering a Tset
TH
of 75 °C and a hysteresis of 5 °C,
the following device can be used:
• MM3488575RRE
For more information, please see the general notes on page 33.