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A3966SLB-T 参数 Datasheet PDF下载

A3966SLB-T图片预览
型号: A3966SLB-T
PDF下载: 下载PDF文件 查看货源
内容描述: 双路全桥式PWM电动机驱动器 [DUAL FULL-BRIDGE PWM MOTOR DRIVER]
分类和应用: 驱动器
文件页数/大小: 9 页 / 805 K
品牌: ALLEGRO [ ALLEGRO MICROSYSTEMS ]
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3966  
DUAL FULL-BRIDGE  
PWM MOTOR DRIVER  
FUNCTIONAL DESCRIPTION  
Internal PWM Current Control. The A3966SA and  
A3966SLB dual H-bridges are designed to drive both  
windings of a bipolar stepper motor. Load current can be  
controlled in each motor winding by an internal fixed-  
frequency PWM control circuit. The current-control  
circuitry works as follows: when the outputs of the H-  
bridge are turned on, current increases in the motor wind-  
ing. The load current is sensed by the current-control  
comparator via an external sense resistor (RS). Load  
current continues to increase until it reaches the predeter-  
mined value, set by the selection of external current-  
The frequency of the internal clock oscillator is set by  
the external timing components RTCT. The frequency  
can be approximately calculated as:  
f
osc = 1/(RT CT + tblank  
)
where tblank is defined below.  
The range of recommended values for RT and CT are  
20 kΩ to 100 kΩ and 470 pF to 1000 pF respectively.  
Nominal values of 56 kΩ and 680 pF result in a clock  
frequency of 25 kHz.  
Current-Sense Comparator Blanking. When the  
source driver is turned on, a current spike occurs due to  
the reverse-recovery currents of the clamp diodes and  
switching transients related to distributed capacitance in  
the load. To prevent this current spike from erroneously  
resetting the source enable latch, the current-control  
comparator output is blanked for a short period of time  
when the source driver is turned on. The blanking time is  
set by the timing component CT according to the equa-  
tion:  
sensing resistors and reference input voltage (VREF  
according to the equation:  
)
I
TRIP = IOUT + ISO = VREF/(4 RS)  
where ISO is the sense-current error (typically 18 mA) due  
to the base-drive current of the sink driver transistor.  
At the trip point, the comparator resets the source-  
enable latch, turning off the source driver of that H-bridge.  
The source turn off of one H-bridge is independent of the  
other H-bridge. Load inductance causes the current to  
recirculate through the sink driver and ground-clamp  
diode. The current decreases until the internal clock  
oscillator sets the source-enable latches of both H-bridges,  
turning on the source drivers of both bridges. Load current  
increases again, and the cycle is repeated.  
tblank = 1900 CT (µs).  
A nominal CT value of 680 pF will give a blanking  
time of 1.3 µs.  
The current-control comparator is also blanked when  
the H-bridge outputs are switched by the PHASE or  
ENABLE inputs. This internally generated blank time is  
approximately 1 µs.  
V
BB  
V
PHASE  
See Enlargement A  
BRIDGE  
BRIDGE ON  
SOURCE OFF  
ALL OFF  
ON  
+
ALL  
OFF  
0
I
OUT  
BRIDGE  
ON  
I
SOURCE  
OFF  
TRIP  
Enlargement A  
t
d
t
R
S
blank  
INTERNAL  
OSCILLATOR  
R
C
T
T
Dwg. WM-003-2  
Dwg. EP-006-16  
www.allegromicro.com  
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