SC1548CSK-1.8TR View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
'SC1548CSK-1.8TR' PDF : 14 Pages View PDF
SC1548
POWER MANAGEMENT
Applications Infomation (Cont.)
It is possible to adjust the output voltage of the fixed
voltage options, by applying an external resistor divider
to the sense pin (please refer to Figure 1 below). Since
the sense pin sinks a nominal 100µA, the resistor
values should be selected to allow 10mA to flow through
the divider. This will ensure that variations in this current
do not adversely affect output voltage regulation. Thus a
target value for R2 (maximum) can be calculated:
R2 ≤
VOUT (FIXED )
10 mA
Ω
The output voltage can only be adjusted upwards from the fixed
output voltage, and can be calculated using the
following equation:
VOUT ( ADJUSTED
)
=
VOUT (FIXED )
• 1 +
R1
R2
+
R1
•
100
µA
Volts
VOUT
Q1
R1
+
C1
100uF
+
C2
100uF
+
C3
22uF
R2
VPWR
12V IN
U1
1 SNS EN 5
2 GND
3 DRV IN 4
SC1548CSK-X.X
ENABLE
C4
0.1uF
VOUT
Figure 1: Adjusting The Output Voltage of Fixed Output Voltage Options
VPWR
12V IN
Q1
R1
+ C1
+ C2
100uF
100uF
R2
+ C3
22uF
U1
1 ADJ EN 5
2 GND
3 DRV IN 4
SC1548CSK
ENABLE
C4
0.1uF
Figure 2: Setting The Output Voltage of the Adjustable Output Voltage Option
Adjustable Output Voltage Option
The adjustable output voltage option does not have an
internal resistor divider. The adjust pin connects directly
to the inverting input of the error amplifier, and the
output voltage is set using external resistors (please
refer to Figure 2 above). In this case, the adjust pin
sources a nominal 0.5µA, so the resistor values should
be selected to allow 50µA to flow through the divider.
Again, a target value for R2 (maximum) can be
calculated:
R2
≤
1.263 V
50 µA
Ω
The output voltage can be calculated as follows:
VOUT
=
1.263
•
1 +
R1
R2
−
0.5µA
•
R1
2004 Semtech Corp.
12
www.semtech.com
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