A3974SED Allegro Microsystems Inc, A3974SED Datasheet - Page 7

• Manufacturer Part Number: A3974SED
• Description: IC MOTOR DRVR PWM DUAL 44-PLCC
• Manufacturer: Allegro Microsystems Inc

Specifications of A3974SED

• Applications: DC Motor Driver
• Number Of Outputs: 2
• Current - Output: ±1.5A
• Voltage - Load: 15 V ~ 50 V
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: -20°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 44-LCC (J-Lead)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

A3974
Serial Interface. The A3974SED is controlled via a 3-wire
(clock, data,strobe) serial port. The programmable functions
allow maximum fl exibility in confi guring the PWM to the mo-
tor drive requirements. The serial data is written as two 20-bit
words: 1 bit to select the word and 19 bits of data. The data is
clocked in starting with D19.
Word 0 Bit Assignments
D0 – D1 Blank Time. The current-sense comparator is blanked
when any output driver is switched on, according to the table
below. f
Select Word 0 (D18 = 0)
Bit
D0
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
D11
D12
D13
D14
D15
D16
D17
D18
D19
osc
D1
is the oscillator input frequency.
0
0
1
1
D0
0
1
0
1
Function
Bridge 1 blank time LSB
Bridge 1 blank time MSB
Bridge 1 off-time LSB
Bridge 1 off-time bit 1
Bridge 1 off-time bit 2
Bridge 1 off-time bit 3
Bridge 1 off-time MSB
Bridge 1 fast-decay time bit LSB
Bridge 1 fast-decay time bit 1
Bridge 1 fast-decay time bit 2
Bridge 1 fast-decay time MSB
Bridge 1 sync. rect. control
Bridge 1 sync. rect. control
Bridge 1 external PWM mode
Bridge 1 enable
Bridge 1 phase
Bridge 1 reference range select
Bridge 1 internal PWM mode
Word select = 0
Test mode
Blank Time
4/f
6/f
12/f
24/f
OSC
OSC
OSC
OSC
DMOS Dual Full-Bridge PWM Motor Driver
FUNCTIONAL DESCRIPTION
D2 – D6 Fixed Off Time. This fi ve-bit word sets the fi xed
off-time for the internal PWM control circuitry. The off-time is
defi ned by
where N = 0 .... 31
For example, with an oscillator frequency of 4 MHz, the fi xed
off-time will be adjustable from 1.75 μs to 63.75 μs in incre-
ments of 2 μs.
D7 – D10 Fast Decay Time. This four-bit word sets the fast-
decay portion of the fi xed off-time for the internal PWM control
circuitry. This will only have impact if mixed-decay mode is
selected (via bit D17). For t
operate in fast-decay mode. The fast-decay portion is defi ned by
where N = 0 .... 15
For example, with an oscillator frequency of 4 MHz, the fast-
decay time will be adjustable from 1.75 μs to 31.75 μs in incre-
ments of 2 μs.
D11 – D12 Synchronous Rectifi cation.
The different modes of operation are described in the synchro-
nous rectifi cation section of the functional description.
D13 External PWM Decay Mode. This bit determines the
current-decay mode when using ENABLE chopping for external
PWM current control.
D12
0
0
1
1
t
t
off
fd
= (8[1 + N]/f
=(8 [1 + N]/f
D13
0
1
D11
0
1
0
1
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
fd
OSC
OSC
> t
Synchronous Rectifi er
Disabled
Low side only
Active
Passive
continued next page ...
] - 1/f
) - 1/f
off
Mode
Fast
Slow
, the device will effectively
OSC
OSC
6