AN709 データシートの表示（PDF） - Vishay Semiconductors
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AN709
Vishay Semiconductors
AN709 Datasheet PDF : 7 Pages
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AN709
Vishay Siliconix
IN
S1
V+
Window
GND
Window
300 ns
S1
–
VDD
+
V+ Transition Window
(300 ns)
200 ns
Figure 4. Short Circuit Protection
GND Transition Window
(200 ns)
Short
Circuit
Detect
FAULT OUTPUT
The FAULT output goes high whenever the Si9976DY detects
an output short circuit or a VDD undervoltage condition. The
detection of the short circuit inhibits operation and sets a fault
latch which is cleared by a rising edge on the enable line, EN.
The VDD undervoltage condition inhibits operation and
indicates a fault but is nonlatching.
TABLE 2: FAULT OUTPUT TRUTH TABLE
EN IN
Condition
FAULT G1
G2
Output Out Out
1
0
Normal Operation
0
1
1
Normal Operation
0
0
X
Disabled
X
1
0
Load Shorted to V+
1
1
1 Load Shorted to Ground
1
1
1 Undervoltage on CBOOT
0
1
0 Undervoltage on CBOOT
0
X
X
Undervoltage on VDD
1
Low
High
Low
Low
Low
Low
Low
Low
High
Low
Low
Low
Low
Low
High
Low
The system-logic supply voltage of 4.5 to 16.5 V can be applied
to VCC to facilitate interfacing of the FAULT output to the user’s
system. If VCC is not supplied, there will be no signal on the
FAULT output. However, the fault protection circuitry will
continue to function as described.
PWM CIRCUITS IN HĆBRIDGES
Anti-Phase Control
The Si9976 was designed to be used in an anti-phase control
strategy. This approach is unique in that the PWM signal
controls both speed and direction with duty cycle alone. Zero
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4
to 50% duty cycle defines zero to full speed in one direction,
50% duty cycle is zero speed, and 50% to 100% duty cycle
defines zero to full speed in the opposite direction. This
approach ensures that the bootstrap capacitor is always
charged, since the H-bridge is continuously switching.
The basic hook-up of an anti-phase H-bridge is very simple.
One half-bridge is driven directly with the PWM signal, and the
other half-bridge is driven with the inverse of the PWM signal
(see Figure 5).
Si9976
IN
Out
A
Dual
LITTLE
FOOT
MOSFET
Out
B
Dual
LITTLE
FOOT
MOSFET
Si9976
IN
Figure 5. Anti-Phase Control
Sign-Magnitude Control
As a secondary function, the Si9976 can be used in
sign-magnitude controls. In this approach, direction of rotation
is determined by the diagonal pair of MOSFETs that are turned
on, and speed is controlled by pulse width modulation of the
active diagonal pair.
The logic required to control the H-bridge is more complex due
to the need to steer the pulse width modulation signal to the
active MOSFET pair. The circuit in Figure 7a applies the PWM
signal only to the low-side active MOSFET.
Document Number: 70582
15-Jun-00
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