16
Remote current programming (External voltage control)
The output current limit of the module can be reduced using an external voltage source connected between the COM and
I
control
pins on the signals connector (J5) as shown below. In practice, this also means that the output can be used as a
modulated or constant current source.
In the diagram above, V
i_out
is an internal voltage source that is proportional to the internal inductor current and approximates
the equation,
V
i_out
= 0.6 + (I
out
/(I
rated
*1.25)), where I
rated
is the maximum rated current for the module.
In this configuration the output current limit will approximate the following equation,
I
limit
= (V
ctrl
-0.6)*I
rated
*1.25, where I
rated
is the maximum rated current for the module.
It is not possible to increase the maximum current limit of the module, and control voltages (V
ctrl
) exceeding 1.53 V will have
no effect on the current limit.
When using an output module as a modulated current source, the output voltage should be manually adjusted to the
maximum that will be required by the application and this will be the upper voltage limit. Once the load is connected, the
output current can then be modulated by applying a control voltage as described above.
Note that the power-good threshold level is fixed and defined by the manually preset voltage. Hence, while the output module
is limiting or modulating the output current this signal may go low.
Output current measurement
The output current of the module can be measured using the I
control
signal. If this pin is unloaded its output voltage will follow
the equation, V
i_out
= 0.6 + (I
out
/(I
rated
*1.25)), where I
rated
is the maximum rated current for the module.
Note that the I
control
output voltage is representative of the internal inductor current not the actual load current. However,
this will only have an influence during dynamic events. It is recommended to add an external amplifier (as shown above left)
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