AN1625 STMicroelectronics, AN1625 Datasheet - Page 4

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

AN1625 APPLICATION NOTE
sees a voltage above V
rent reverses direction and flows into the bulk capacitor. It turns out that the highest differential voltage is ob-
served between two OUT pins when a phase change turns a high-side off during an off-time, and this must
always be kept below 60 V [2].
Figure 3. Currents and voltages if a phase change turns a high-side off during off-time.
Figure 4 shows the voltage waveforms at the OUT pins referring to a possible practical situation, with a peak
output current of 2.8 A, V
ground spike amplitude is -2.64 V for one output; the other OUT pin is at about 55 V. In these conditions, total
differential voltage reaches almost 60 V, which is the absolute maximum rating for the DMOS. Keeping differ-
ential voltage between two Output pins within rated values is a must that can be accomplished with proper se-
lection of Bulk capacitor value and equivalent series resistance (ESR), according to current peaks and adopting
good layout practices to minimize PCB parasitic inductances (see below) [2].
Figure 4. Voltage at the two outputs if a phase change turns a high-side off during off-time.
4/39
on-time
S
, due to voltage drop across the high-side (integrated) freewheeling diode, as the cur-
S
= 52 V, R
SENSE
OUT2
OUT1
= 0.33 , TJ = 25 °C (approximately) and a good PCB layout. Below
off-time
SENSE
Equivalent
Capacitor
Circuit
R
Bulk
SENSE
*I+ V
F(Diode)
ESR
ESL
PCB Parasitic
Inductance
a phase change can occur
during off-time
R
SENSE
*I
V
S
PCB Parasitic
Inductance
third half bridge
Current starts
flowing in the