EUP2539
Shutdown Voltage vs. Input Voltage
1
0.8
0.6
0.4
0.2
-40
℃
-25
℃
85
℃
125
℃
3
3.5
4
4.5
5
Figure 6. Filtered PWM Dimming Control
Filtered PWM Dimming (0V to 2.5V)
Input Voltage (V)
Figure 9.
25
20
15
10
5
Enable to Open LED Waveforms
VEN
2V/div
VOUT
20V/div
0
0
10 20 30 40 50 60 70 80 90 100
PWM Duty Cycle (%)
SW
20V/div
Figure 7.
50.0µs/div
Open Load Shutdown
Figure 10.
In the event of an “Open LED” fault condition, the
EUP2539 will continue to boost the output voltage with
maximum power until the output voltage reaches
approximately 38V. Once the output exceeds this level,
the device will cease operation until the EN pin is cycled
off and on.
Thermal Shutdown
Thermal overload protection circuitry has been included
to prevent the device from operating at unsafe junction
temperatures above 150ºC. In the event of a thermal
overload condition the device will automatically
shutdown and wait till the junction temperatures cools to
130ºC before normal operation is resumed.
Capacitors Selection
A 4.7µF to 10µF ceramic input capacitor (CIN) and a
0.22µF to 4.7µF ceramic output capacitor (COUT) are
sufficient for most applications. During Direct PWM
Dimming control,
a larger output capacitor will
significantly reduce audio noise induced by output
capacitor, and a smaller will enlarge the audio noise, a
2.2uF COUT is recommended. Under normal condition, a
4.7µF input capacitor is sufficient. For applications with
higher output power, a larger input capacitor of 10µF
may be appropriate. X5R and X7R capacitor types are
ideal due to their stability across temperature range.
Figure 8. Open LED Protection
DS2539 Ver1.1 Apr. 2009
9
EUTECH [ EUTECH MICROELECTRONICS INC ]
