Analog Devices DC2733A Demo Manual page 4

DEMO MANUAL DC2733A
QUICK START PROCEDURE
CURRENT
FLOW
+
-
KELVIN
GROUND
Figure 1. Source and Load Connections. Current Return Outside
of Board.
Connect input power supplies to IN1 and IN2 inputs, and
connect independent loads to OUT1 and OUT2 ports, as in
Figure 1. The same input supply may connect to both IN1
and IN2. The LTC4249 draws power from the IN1 port,
so powering IN1 is a minimal requirement. Driving IN2
is optional. If channel 2 is unused tie IN2 to GND. OUT2
may be left floating.
The board has several connections labeled GROUND.
When connecting power supplies and loads, the cur-
rents naturally flow from INn pins, through the LTC4249,
then out through the OUTn pins. On the current return
path, however, it is best to avoid ground currents flowing
through the GROUND plane of the demo board. Instead,
connect a single wire from ground near the power sup-
plies to one of the GROUND connections on the board,
forming a Kelvin connection back to the system ground
point. This avoids load currents flowing through the
GROUND plane on the board. See Figure 1.
In the configuration of Figure 1 when the forward current
through CH1 exceeds the programmed circuit breaker
threshold the channel will turn off. The current through CH2
will be unaffected. Re-enable a channel by toggling ENn.
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It is also possible to use channels in parallel, as shown in
Figure 2. Channels will share current, but remember that
channel impedances are not perfectly matched, so cur-
rents will share slightly unevenly. When the circuit breaker
trips it will trip in one channel first, followed quickly by
the other channel, usually within about 20μs.
CURRENT
FLOW
+
-
KELVIN
GROUND
Figure 2. Parallel Channel Operation
A transient fault will trip the circuit breaker then allow the
LTC4249 to restart after the retry interval. A fault lasting
longer than 3 seconds (3 retries) will result in a persistent
off condition. Clear a faulted channel by toggling ENn low
then high.
The demo board has 10kΩ resistors at both of the IMON
pins. This is the recommended value to give a circuit
breaker current threshold of 1.2A (1.2V on IMON). While
10kΩ is the smallest recommended resistor value, it is
possible to replace R1 and R2 on the board with larger
valued resistors to lower the circuit breaker current
threshold. The relationship between resistance and CB
threshold is:
1.2 • 10k
I
=
CB
R
IMON
Note that circuit breaker accuracy is directly related to the
accuracy of R1 and R2. We use 0.1% resistor tolerance
for best results.
In addition to controlling the circuit breaker, the IMON pins
can be used by an external circuit to read channel current.
(1)
Rev. A