AN1625 STMicroelectronics, AN1625 Datasheet - Page 8

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

AN1625 APPLICATION NOTE
duce the inductance.
R
The following table shows R
examples of current peak values.
2.6 Charge pump external components
An internal oscillator, with its output at CP pin, switches from GND to 10 V with a typical frequency of 600 kHz
(see Figure 7).
Figure 7. Charge Pump.
When the oscillator output is at ground, C5 is charged by V
biased and the charge flows from C5 to C8 through D1, so the V
imum voltage of V
With a differential voltage between V
current drawn by the V
Resistor R4 is added to reduce the maximum current in the external components and to reduce the slew rate of
the rising and falling edges of the voltage at the CP pin, in order to minimize interferences with the rest of the
circuit. For the same reason care must be taken in realizing the PCB layout of R4, C5, D1, D2 connections (see
also the Layout Considerations section). Recommended values for the charge pump circuitry are:
8/39
SENSE
tolerance reflects on the peak current error: 1% resistors should be preferred.
0.5
1.5
I
pk
1
2
S
+ 10 V - V
BOOT
10 V
f =
SENSE
pin is 1.85mA.
V
600
S
D1
+ 10 V - V
kHz
V
R
BOOT
- V
SENSE
To High-Side
Gate Drivers
recommended values (to have 0.5V drop on it) and power ratings for typical
D2
S
D1
, which supplies the high-side gate drivers.
D1
and V
- V
0.33
0.25
0.5
C5
R4
Value [ ]
CP
1
D2
BOOT
10 V
D2
V
R
SA
R
of about 9V and the bridges switching at 50 kHz, the typical
DS (ON)
DS(ON)
V
S
V
V
+ 10 V - V
SB
= 70
S
= 70
- V
R
D1
SENSE
C8
D1
S
through D2. When it rises to 10 V, D2 is reverse
Charge Pump
f = 600 kHz
Oscillator
BOOT
Power Rating [W]
10 V
0.25
0.75
L6235
0.5
1
5 V
pin, after a few cycles, reaches the max-
2 X 1 , 0.25W paralleled
3 X 1 , 0.25W paralleled
4 X 1 , 0.25W paralleled
Alternatives