AMG-XB404 Datasheet, PDF (36/73 Pages) alpha microelectronics gmbh – Fully Integrated Single Motor Controller for Electrical Motors

AMG-XB404
Fully Integrated Single Motor Controller for Electrical Motors
transformer winding as the output voltage VAUX.
The constant switching frequency of the SMPS can be determined by a low-precision RC oscillator
which is part of the SMPS, or by an adjustable, digitally generated reference clock signal which is
adjustable via the IO expander (see section 5.2 p. 9). At start-up when no digitally generated clock
is available, the RC oscillator is used. Typically, the RC oscillator's frequency is significantly lower
than the optimum switching frequency to accommodate the oscillator's lack of precision. This
means that less than the rated power can be drawn at start-up. To achieve full performance the
SMPS must be operated using the well-defined, digitally generated switching frequency.
The SMPS is supplied through the SWVDD pin and must be biased for start-up. Zener diodes are
used to provide the supply voltage for the level shifter and SMPS. The SMPS's internal reference
voltage at the SWVREF pin needs to be stabilized using a capacitor connected to DGND. The
SMPS shares the digital ground pin DGND with the rest of the IC.
As shown in figure 19 a secondary winding of the transformer can be used to derive a secondary,
indirectly regulated output voltage, helping to improve over-all efficiency.
In the presence of low loads the SMPS enters a cycle skipping mode.
The SMPS is designed to limit the maximum power via the duty cycle of the switching signal. The
shunt resistor R4 must be dimensioned in such a way that the transformer's specifications are not
exceeded for the given switching frequency, the highest possible voltage across R4 (approx.
1.26V), and the given regulated output voltage. If this maximum load is exceeded for a duration of
more than one second (typical) the SMPS's output will be disabled in order to protect the circuit.
The secondary switching output is short-circuit protected by monitoring the power-on reset signal.
If the voltage present at the digital 5V pin of the AMG-XB404 remains below the minimum
operating voltage for longer than one second the SMPS's output will be disabled in order to protect
the circuit.
The AMG-XB404 requires a power-on cycling to resume to normal operation after the occurrence
of one of the error conditions described above.
AMG-XB404
Revision: A
2. Nov. 2012 © All rights reserved
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