sp7600 Exar Corporation, sp7600 Datasheet - Page 12

• Manufacturer Part Number: sp7600
• Description: 2amp, 29v Buck Converter For Led Driver Applications
• Manufacturer: Exar Corporation

Typical Performance Characteristics
The typical performance characteristics follow and begin with an illustration of the efficiencies that
can be obtained with the SP7600 driving white LEDs in parallel for up to 3A total current or in series
for 6 LEDs at up to 2A 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 2A or 3A 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 especially the inductor current signal ILX.
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.
12/17/07 rev: A
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SP7600
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©Copyright 2007 Exar Corporation
SP7600