AMIS-30421 Datasheet, PDF (13/41 Pages) ON Semiconductor – Micro-Stepping Stepper Motor Bridge Controller

AMIS−30421
FUNCTIONAL DESCRIPTION
H−Bridge Pre−Drivers
The H−bridge pre−drivers for external N−type MOSFETs
are controlled by means of current sources for slope
regulation (Figure 10). The current source value can be set
through SPI (see p35 and further). During the MOSFET
switch−on and switch−off phase this current source will be
applied for a certain time (respectively t_on and t_off where t_on
is divided in t₁ and t₂). After this time (t_on or t_off) the gate of
the MOSFET is pulled high or low by means of a switch
(SW_on or SW_off). The timings can also be set through SPI
(see p37 and further).
To prevent short circuits, an additional time t_nocross can be
added between switching off one MOSFET and switching
on the other MOSFET of a half H−bridge (SPI bits
<NO_CROSS[1:0]>).
More information on the current sources and timings can
be found in Table 5. A detailed description of the SPI
settings for the H−bridge pre−drivers can be found at p31
and further.
Figure 11 gives a detailed view on the different stages
during switching of the MOSFET.
Ion
SWon
External
MOSFET
I_off
SW_off
AMIS−30421
Figure 10. Pre−driver Topology
V_gate
5
1
2
3
I_ON1
I_ON2
4
5
I_OFF
t1
t2
t_on
t
t_off
t_nocross
Figure 11. Detailed View on MOSFET Switching
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