AVR430
9
8124C-AVR-10/08
4.1.4 Hall sensors
VHall (VHa) is available on J7 as power source for Hall sensors, typically found on
BLDC motors. With J1 VHa can be connected to Vcc or to a 5V regulator (U2). A
separate 5V regulator for the Hall sensors is included so Vcc can be 3,3V while using
Hall sensors, since most Hall sensors will not work on 3,3V.
4.2 Half bridges
The half bridge consists of two n-channel power MOSFETs, driven by an integrated
high and low side driver IC (IR2101S). The integrated driver IC is powered from Vin
and provides gate voltages to the high and low side power MOSFETs. Schematics for
the half bridge for phase U is shown in Figure 4-2
Figure 4-2.
Phase U half bridge.
4.2.1 High side driving considerations
The high side of the half-bridge uses a bootstrap circuit. This means the duty cycle
and the on-time are limited by the requirement to refresh the charge in the bootstrap
capacitor. If the driving logic fails to do this, the gate voltage to the high side MOS will
decrease and the R
DS
will increase. This may result in high power dissipation in the
high side MOS, and consequently destroy it.
Refer with IR2101S datasheets for detailed information about the bootstrap circuit.
4.2.2 Test points
Each half bridge has several testpoints to allow for measurements. MOS gate
voltages for high (VGh) and low-side (VGl) and bootstrap voltage (Vboot) are
available. Both sides of the shunt resistors (- and +) can also be measured.
