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Operation
The SC120/SC121 EVB provides confi guration options for
any SC120 or SC121 application. The following describes
the standard confi guration. If an EVB is requested with a
non-standard confi guration, some of the standard values
or confi gurations will diff er from this description.
The output voltage can be set to 3.3V using internal pro-
gramming by installing a jumper on JP1. Any other
voltage from 1.8V to 5.0V can be programmed using resis-
tors R1, R2, R6, and capacitor C5. R1 and R2 are the
programming resistors described in the datasheet, there
designated R
and R
, respectively. The EVB is provided
1
2
with R1 = 499kΩ and R2 = 1MΩ, for an output voltage of
1.8V. R6 is in series with R1, and is useful for obtaining
high values for R
as the sum of R1 and R6, or for dividing
1
R
into two resistors to mitigate environmental concerns if
1
a large value of R
is desired. The EVB is provided with
1
R6 = 0Ω. C5 is also described in the datasheet, there des-
ignated C
. It is used to improve the PSAVE ripple
FB
amplitude if needed, as described in the datasheet. The
EVB is provided with C5 removed.
The input supply is connected using banana jacks J1. The
IN sense test point (TP3) is provided for input monitoring,
or for Kelvin sense feedback to the input supply. The
output load is connected using banana jacks J2. The OUT
sense test point (TP6) provides a sense connection to the
output capacitor. Two sets of capacitor pads are provided
for both the input and output capacitors to permit devices
of diff erent package sizes, either 0805 or 1206.
The enable pin is pulled up to IN with a 100kΩ resistor, R3.
The pushbutton switch connects EN to ground to disable
the SC120/SC121 when the button is in the up position.
When the pushbutton is in the down position, the switch
is open, EN is pulled high, and the SC120/SC121 is
enabled.
The inductor is connected from IN to LX by one of three
methods. A jumper can be installed on JP1 to complete
the inductor current path from the input supply. A wire
loop can be connected across JP1 for use with a current
probe to monitor inductor current. R4 is in parallel with
JP1. A shorting bar is included soldered to only one R4
pad. Replace the shorting bar across both R4 pads to
bypass the current sense loop. A Tektronix scope probe
connection point (PTP2) is provided to monitor the LX pin
voltage. Alternatively, LX pin voltage can be monitored
using TP1.
R5 is an unpopulated resistor pad that is provided for con-
nection of a fi xed load resistor directly on the board.
SC120/SC121 EVB
9
9
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