EVAL6229PD STMicroelectronics, EVAL6229PD Datasheet - Page 11

• Manufacturer Part Number: EVAL6229PD
• Description: EVAL BOARD FOR L6229PD SOIC
• Manufacturer: STMicroelectronics

Specifications of EVAL6229PD

• Mfg Application Notes: L6235, AN1625 App Note
• Main Purpose: Power Management, Motor Control
• Embedded: No
• Utilized Ic / Part: L6229PD SOIC
• Primary Attributes: 3-Ph BLDC, 8 ~ 52V Output, PWM Current Control, Brake Function
• Secondary Attributes: Over Current, Cross Conduction & Temperature Protection
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-5491

2.8 Reference Voltage for PWM Current Control
The device has two analog inputs, V
peak value of the motor current through the integrated PWM circuitry. In typical applications these pins are con-
nected together, in order to obtain the same current in the two motor windings (one exception is the microstep-
ping operation; see the related section). A fixed reference voltage can be easily obtained through a resistive
divider from an available 5 V voltage rail (maybe the one supplying the µC 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
(see Figure 9).
Assuming that the PWM output swings from 0 to 5V, the resulting voltage will be:
where D
Assuming that the µC output impedance is lower than 1k
µC PWM switching from 0 to 5V at 100kHz, the low pass filter time constant is about 0.12 ms and the remaining
ripple on the V
but the reference voltage will take more time to vary after changing the duty-cycle of the µC PWM, and too high
values of R
As sensing resistor values are typically kept small, a small noise on V
error in the output current. It's then recommended to decouple these pins with ceramic capacitors of some tens
of nF, placed very close to V
to GND, zero current is not guaranteed due to voltage offset in the sense comparator. The best way to cut down
(IC) power consumption and clear the load current is pulling down the EN pin. In slow decay, with very small
reference voltage, PWM integrated circuitry can loose control of the current due to the minimum allowed dura-
tion of t
Figure 9. Obtaining a variable voltage through a PWM output of a µC.
ON
µC
(see the Programmable off-time Monostable section).
LP
is the duty-cycle of the PWM output of the µC.
will also increase the impedance of the V
ref
voltage will be about 20 mV. Using higher values for R
ref
and GND pins. Note that V
PWM Output
refA
of a µC
and V
V
re f
refB
=
R
, connected to the internal sense comparators, to control the
LP
5V D
---------------------------------------- -
R
R
ref
DIV
LP
ref
net at low frequencies, causing a poor noise immunity.
+
C
pins cannot be left unconnected, while, if connected
R
with R
DIV
R
DIV
GND
LP
= 56k , R
C
ref
LP
LP
V
input pins might cause a considerable
AN1451 APPLICATION NOTE
ref
, R
DIV
DIV
and C
= 15k , C
LP
will reduce the ripple,
LP
= 10nF and a
11/43