ML4425CP 查看數據表（PDF） - Fairchild Semiconductor
零件编号
产品描述 (功能)
生产厂家
ML4425CP Datasheet PDF : 16 Pages
| |||
PRODUCT SPECIFICATION
ML4425
The maximum frequency on the VCO pin is found by:
fMAX = 0.05 × N × RPMMAX
(3)
CVCO
RVCO
The voltage at the VCO/TACH pin is equal to the rotor
speed. The voltage at SPEED FB is controlled by the back
EMF sampler.
Back EMF Sampler
The input to the voltage controlled oscillator is the back
EMF sampler. The back EMF sense pins FB A, FB B, and
FB C inputs to the back EMF sampler require a signal from
the motor phase leads that is below the VDD of the ML4425.
The phase sense input impedance is 8kΩ. This requires a
series resistor RES1 from the motor phase lead as shown in
Figure 6 based on the following equation:
RES1 = 670Ω ⁄ V × (VMOTOR – 10V)
(4)
The back EMF sampler takes the motor phase voltages
divided down to signals that are less than VDD (12V nomi-
nal) and calculates the neutral point of the motor by the fol-
lowing equation:
Neutral = P-----H-----1----+-----P-----H3----2-----+-----P----H-----3--
(5)
This allows the ML4425 to compare the back EMF signal to
the motor’s neutral point without the need for bringing out an
extra wire on a WYE wound motor. For DELTA wound
motors there is no physical neutral to bring out, so this refer-
ence point must be calculated in any case.
SPEED CVCO
FB
RVCO
FROM
BACK EMF
SAMPLER
& RAMP
GENERATOR
RESET
(FROM CAT)
VOLTAGE
CONTROLLED
OSCILLATOR
VCO/TACH
4.3V
CVCO
2.3V
5V
VCO/TACH
0V
Figure 5. External VCO Component Connections
The back EMF sampler measures the motor phase that is not
driven (i.e. if LA and HB are on, then phase A is driven low,
phase B is driven high, and phase C is sampled). The sam-
pled phase provides a back EMF signal that is compared
against the neutral of the motor. The sampler is controlled by
the commutation state machine. The sampled back EMF is
compared to the neutral through an error amplifier. The out-
put of the error amplifier outputs a charging or discharging
current to SPEED FB, which provides the control voltage to
the VCO.
MOTOR ΦA
MOTOR ΦB
MOTOR ΦC
RES1
RES2
RES3
FB A
FB B
FB C
4kΩ 4kΩ 4kΩ
NEUTRAL
SIMULATOR
ΦA + ΦB + ΦC
6
MULTIPLEXER
SIGN
CHANGER
1
gm = 8kΩ
+
–
TO
SPEED FB
4kΩ 4kΩ 4kΩ
F/R
F/R
COMMUTATION
STATE MACHINE
Figure 6. Back EMF Sampler Detailed Block Diagram
REV. 1.0.2 7/2/01
9
Share Link: 