APPLICATION NOTES
Operation
Remote Sense
The remote sense feature of the SLC100 can be used
to compensate for voltage drops in the output power
lines by sensing output voltage directly at the point of
load. To enable this feature, connect the +Sense and
–Sense pins to the +Vout and –Vout pins, respective-
ly, at the point in the circuit where the tightest regula-
tion is required (Figure
1).
The sense leads conduct
very little current compared with the power leads and
therefore provide a more accurate indication of load
voltage for regulation purposes. This enables the
converter to increase (or decrease) its output volt-
age to compensate for any load distribution losses,
allowing for a more precise load voltage. Refer to the
product data sheet for the maximum output voltage
compensation range of the sense function.
When using remote sense with dynamic loads, the
transient response at the point of load may be limited
by the inductance present in the power lines. Severe
load steps may require the addition of a capacitor
C
L
across the output lines. When the load demands
an immediate increase in load current, this capacitor
helps to supply a portion of the current and reduces
the burden on the converter.
When the load is physically distanced from the con-
verter, the inductance of the power leads, and any by-
pass conductance at the load, can result in increased
phase shift in the converter’s feedback loop, causing
instability. This situation can be eliminated by insert-
ing bypass capacitors (C
B
) from the outputs to the
sense leads directly at the output pins. These capaci-
tors de-couple any AC on the power lines and assure
that only the DC voltage is sensed.
If remote sensing is not desired then +Sense and
-Sense must be tied to their respective outputs
for proper operation.
•
•
Output Voltage Trim
Figure 1 – Remote Sensing Circuit
The SLC100’s output voltage may be adjusted high
or low by an amount indicated on the product data
sheet. As shown in
Figure 2,
to raise the converter’s
output voltage a resistor must be placed between the
Trim pin and +Vout pin.
In general, the line resistance, or load drop, between
the output pins of the converter and load should be
minimized. Using remote sense, a large line resis-
tance, with a regulated load voltage, will result in
a higher output voltage at the output of the DC/DC
Converter. To prevent exceeding the converter’s
output power limits, a higher output voltage will
require a reduction in the maximum allowable output
current in accordance with the voltage/current power
relationship. To minimize the line resistance between
the converter and the load, the converter should be
placed as close to the load as possible. Line resis-
tance can further be decreased by using heavy gauge
wire or by increasing the cross sectional area of the
PC board traces.
Figure 2 – Trim Up Circuit
Product: www.cdpoweronline.com
SLC100 1.2V Rev C 11/2004
5
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