AN1625 STMicroelectronics, AN1625 Datasheet - Page 3

• Manufacturer Part Number: AN1625
• Description: L6235 THREE PHASE BRUSHLESS DC MOTOR DRIVER
• Manufacturer: STMicroelectronics

2
2.1 Current Ratings
With MOSFET (DMOS) devices, unlike bipolar transistors, current under short circuit conditions is, at first ap-
proximation, limited by the R
and the two V
values are meant to avoid damaging metal structures, including the metallization on the die and bond wires. In
practical applications, though, maximum allowable current is less than these values, due to power dissipation
limits (see Power Management section).
The device has a built-in Over Current Detection (OCD) that allows protection against short circuits between the
outputs and between an output and ground (see Over Current Detection Section).
2.2 Voltage Ratings and Operating Range
The L6235 requires a single supply voltage (V
5V and 10 V required for the internal circuitry. The operating range for V
undesirable low supply voltage an Under Voltage Lock Out (UVLO) circuit shuts down the device when supply
voltage falls below 6 V; to resume normal operating conditions, V
vided to avoid false intervention of the UVLO function during fast V
DMOS's R
affected, and this is particularly true for the High Side DMOS that are driven from V
obtained through a charge pump from the internal 10V supply, which will tend to reduce its output voltage when
V
supply voltage (V
Figure 2. High side gate drivers supply voltage versus supply voltage.
Note that V
for the two H-bridges. The integrated DMOS have a rated Drain-Source breakdown voltage of 60 V. However
V
V
the other outputs (OUT2 in Figure 3) is high (during the off-time all active bridges turn their high-side on) the
load current starts flowing in the low-side freewheeling diode and the SENSE pin sees a negative spike due to
a not negligible parasitic inductance of the PCB path from the pin to GND. This spike is followed by a stable
negative voltage due to the drop on R
voltage due to the forward recovery time of the integrated freewheeling diode and the forward voltage drop
across it. Typical duration of this spike is 30 ns. At the same time, the OUT2 pin (in the example of Figure 3)
S
S
S
should be kept below 52 V, since in normal working conditions the DMOS see a Vds voltage that will exceed
supply. In particular when a high-side DMOS turns off due to a phase change (OUT1 in Figure 3), if one of
goes below 10V. Figure 2 shows the supply voltage of the high side gate drivers (V
DESIGNING AN APPLICATION WITH L6235
V
BOOT
DS(ON)
[V]
S
must be connected to both V
SA
- V
and V
S
S
is a function of the V
).
7 .6
7 .2
6 .8
6 .4
SB
8
6
pins are rated for a maximum of 2.8 A r.m.s. and 5.6 A peak (typical values). These
DS(ON)
8
of the DMOS themselves and could reach very high values. L6235 Out pins
S
SENSE
supply voltage. Actually, when V
8 .5
SA
and V
. The output pin sees a similar behavior, but with a slightly larger
S
), for the motor supply. Internal voltage regulators provide the
SB
because the bootstrap voltage (at V
9
V
S
[V]
S
9 .5
must then exceed 7 V. The hysteresis is pro-
S
ringings. It should be noted, however, that
S
S
is less than 10V, R
AN1625 APPLICATION NOTE
is 8 to 52 V. To prevent working into
1 0
BOOT
BOOT
supply. This supply is
BOOT
1 0 .5
DS(ON)
- V
pin) is the same
S
) versus the
is adversely
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