ML4425CP Ver la hoja de datos (PDF) - Fairchild Semiconductor
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ML4425CP Datasheet PDF : 16 Pages
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ML4425
PRODUCT SPECIFICATION
Cross Conduction Comparator
When the ML4425 goes from align mode into ramp mode,
there is a possibility of cross conduction in phase 3 of the
bridge power stage. This cross conduction can happen when
HC is on in the align mode shown as state R in Table 1, and
the controller transitions to state A in ramp mode where HC
is turned off and LC is turned on. Cross conduction can
appear due to the differences in turn on and turn off times of
the power devices. To solve this problem, the LC output
driver is gated off until the HC is equal to VDD – 3V as
shown in Figure 10.
Braking
When the BRAKE pin is pulled below 1.4V, the low side
output drivers LA, LB, and LC are turned on and the high
side output drivers HA, HB, HC are turned off. Braking
causes rapid deceleration of the motor and current limiting is
de-activated, and care should be taken when using the
BRAKE pin. BRAKE is has an internal 4kΩ pull-up as
shown in Figure 10, and can be driven by a switch to ground,
an open collector or drain logic signal, or a TTL logic signal.
Undervoltage Lockout
Undervoltage lockout is used to protect the 3-phase bridge
power stage from a low VDD condition. Undervoltage is trig-
gered at VDD of 9.5V or less and is indicated by a TTL low
output on the UV FAULT pin. Undervoltage lockout also
turns off all output drivers (LA, LB, LC, HA, HB, and HC).
The comparator that triggers undervoltage lockout has
150mV of hystresis.
The most flexible configuration is to use high side drivers to
control N-Channel MOSFETs (or IGBTs) which allows
applications from less than 12V up to 600V. Figure 12 shows
the interface between the ML4425 and IR2118 high side
drivers from International Rectifier. This configuration is
capable of driving motors from busses of up to 320V. The
BRAKE pin can be pulsed prior to startup with an RC
circuit. This charges the bootstrap capacitors (C19, C20, and
C21) for the three high side drivers, allowing the reset phase
to operate normally. These capacitors must be sized so that
they stay sufficiently charged during the align mode. Refer to
AN-43 for additional applications information on the
ML4425.
FROM
COMMUTATION
STATE MACHINE
FROM
SPEED CONTROL LOOP
& CURRENT LIMIT
1.4V
VDD
–
+
9.5V +
–
GATING
LOGIC
&
OUTPUT
DRIVERS
4kΩ
REFERENCE
HA
2
HB
3
HC
4
LA
9
LB
10
LC
11
UV FAULT
18
BRAKE
25
VDD
GND
RREF VREF
14
28
27
7
Design Considerations
Figure 10. Cross Conduction, Brake, and UVLO Circuits
Interfacing to a 3-Phase Bridge Power Stage
The ML4425 output drivers are configured to drive a 3 phase
bridge power stage. For applications with buss voltages from
12V up to 80V, level shifting circuitry can be used to drive
higher voltage P-channel MOSFETS for the high side
switches as shown in Figure 11.
12
REV. 1.0.2 7/2/01
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