XRP7604 Datasheet, PDF (5/13 Pages) Exar Corporation – 1A 29V Non-Sync. Buck High Power LED Driver

XRP7604
1A 29V Non-Sync. Buck High Power LED Driver
TYPICAL PERFORMANCE CHARACTERISTICS
The typical performance characteristics follow and begin with an illustration of the efficiencies that
can be obtained with the XRP7604 driving 1 or 6 white LEDs in series for up to 500mA output
current. For the 6 LED applications with a 24V input, the duty cycle is high and an efficiency of
94% can be obtained. For 12V input and 1 LED at 1A output, the duty cycle is much lower, but the
efficiency is still over 80%. Note: to improve line regulation a small 22pF ceramic capacitor C6
should be placed from VFB to GND to filter out any noise obtained on the sensitive FB pin.
Scope photos of output ripple are shown for the typical application circuit for 6V input at 150mVpp
ripple and at 29V input with over 400mVpp output ripple, both shown with no output capacitor. For
comparison, an output ripple scope photo is shown with only 70mVpp when a 1uF capacitor is used
at the output. For applications sensitive to output ripple, adding this relatively small 1206 sized 1uF
50V ceramic capacitor to the output provides a very good reduction in output ripple but since the
value is only 1uF the circuit will still provide good PWM output response.
Vin startup scope photos are shown for 6V, 12V and 29V input with no problems in startup as
shown in the Vout, VFB and the outpt current Io.
The last scope photos are for the output short circuit which causes a hiccup mode. The output can
be shorted which causes a controlled automatic reset or hiccup mode of about 50 to 100msec
period.
All data taken at V_IN = 12V, T_A = 25°C, unless otherwise specified - Schematic and BOM from Application Information
section of this datasheet.
Efficiency versus Vin at Iout = 750mA
100
1 LED
2 LED
3 LED
6 LED
90
80
70
60
5
10
15
20
25
30
Vin (V)
Fig. 4: Efficiency vs Input Voltage
0.800
0.775
Iout versus Vin
1 LED
2 LED
3 LED
6 LED
0.750
0.725
0.700
5
10
15
20
25
30
Vin (V)
Fig. 5: Output Current vs Input Voltage
© 2009 Exar Corporation
5/13
Rev. 1.0.0