QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 474
4A, 500KHZ STEP DOWN SWITCHING REGULATOR
4.
To turn the circuit off, ground the
terminal labeled SHDN
5.
To test the synchronization feature
of the demo board apply a sync sig-
nal to the sync terminal and note
the shift in the operating fre-
quency. The Sync signal should have
an amplitude greater than 2.2V,
duty cycle of between 10% and 90%
and a frequency of 580kHz–1000kHz
MEASUREMENT NOTES
Voltage measurements
The correct way to measure voltage is
at the terminal of the demo board.
Attempts to measure output voltage at
the load will result in a too low
output voltage due to wiring loss.
This is especially true at high cur-
rent. Needless to say any efficiency
calculation should be made using demo
circuit terminal voltages as opposed
to load or power source terminal
voltages.
Ripple Voltage Measurements
The ceramic capacitors used in this
demo board have almost no ESR and are
extremely effective filters. In order
to correctly measure output ripple
voltage correct technique is impor-
tant. The scope ground lead and
sheath should be removed and the out-
put ripple measured by placing the
scope probe directly across the out-
put Vout and GND pins as illustrated
in Figure 4.
5V TO 25V
SUPPLY
25W
+
–
+
–
+
–
+
–
+
–
+
–
LOAD
Figure 3.
Proper Measurement Equipment Setup
2
