AN4243 Datasheet, PDF (12/29 Pages) STMicroelectronics – The L6230 DMOS driver for three-phase brushless DC motor

Designing an application with the L6230
AN4243
2.7
Sharing the charge pump circuitry
If more than one device is used in the application, it is possible to use the charge pump from
one L6230 to supply the V_BOOT pins of several ICs. The unused CP pins on the slave
devices are left unconnected, as shown in Figure 8. A 100 nF capacitor (C_boot2) should be
connected to the V_BOOT pin of each device. Supply voltage pins (V_S) of the devices sharing
charge pump must be connected together.
The higher the number of devices sharing the same charge pump, the lower the differential
voltage available for gate drive (V_BOOT - V_S), causing a higher R_DS(on) for the high-side
DMOS, so higher dissipating power.
A better performance can also be obtained using a 33 nF capacitor for C_fly and using
Schottky diodes (for example BAT47 are recommended).
Sharing the same charge pump circuitry for more than 3 or 4 devices is not recommended,
since it reduces the V_BOOT voltage increasing the high-side MOS on-resistance and thus
power dissipation.
Figure 8. Sharing the charge pump circuitry
To other Devices
Cboot2
D1
D2
Cfly1
Cboot1
VBOOT
CP
VSA VSB
VBOOT
CP
VSA VSB
L6230
To High - Side
L6230
To High - Side
L6230
AM16570v1
2.8
How to generate a reference voltage for the current control
The device has an analog input (CP-) connected to the internal comparator, that can be
used to control the peak value of the motor current through an external control loop.
A fixed reference voltage can be easily obtained with a resistive divider from an available
pull-up voltage rail (maybe the one supplying the microcontroller or the rest of the
application) and GND.
A very simple way to obtain a variable voltage without using a DAC is to low-pass filter a
PWM output of a µC (Figure 9).
12/29
Doc ID 024199 Rev 1