A3992 Datasheet, PDF (6/13 Pages) Allegro MicroSystems – DMOS Dual Full-Bridge Microstepping PWM Motor Driver

A3992
DMOS Dual Full-Bridge
Microstepping PWM Motor Driver
Word 1 Bit Assignments
Word 1 is selected by setting D0 = 1. Assignments are
summarized in the following table, and desribed in
detail in the remainder of this section.
Word 1 Bit Assignments
Bit
Function
D0
Word Select = 1
D1
Blank Time LSB
D2
Blank Time MSB
D3
Off Time LSB
D4
Off Time Bit1
D5
Off Time Bit2
D6
Off Time Bit3
D7
Off Time MSB
D8
Fast Decay Time LSB
D9
Fast Decay Time Bit1
D10
Fast Decay Time Bit2
D11
Fast Decay Time MSB
D12
C0 Oscillator Control
D13
C1 Oscillator Control
D14
SR Control Bit 1
D15
SR Control Bit 2
D16
Reserved for testing
D17
Reserved for testing
D18
Idle Mode
D1 – D2 Blank Time. 2 bits to set the blank time scal-
ing factor for the current sense comparator:
D2
D1
Time
0
0
4 × P_OSC
0
1
6 × P_OSC
1
0
8 × P_OSC
1
1
12 × P_OSC
When a source driver turns on, a current spike occurs
due to the reverse recovery currents of the clamp di-
odes and/or switching transients related to distributed
capacitance in the load. To prevent this current spike
from erroneously resetting the source enable latch,
the sense comparator is blanked. The blank timer runs
after the off time counter to provide the programmable
blanking function. The blank timer is reset when
PHASE is changed.
D3 – D7 Fixed Off Time. 5 bits to set the fixed
off-time for the internal PWM control circuitry. Fixed
off-time is defined by:
t_OFF = (1 + n) × P_OSC × 8 – P_{OSC ,}
where n = 0 to 31.
For example, with a master oscillator frequency of
4 MHz ( P_OSC = 250 ns), the fixed off-time is adjust-
able from 1.75 to 63.75 μs, in increments of 2 μs.
D8 – D11 Fast Decay Time. 4 bits to set the fast
decay portion of fixed off-time for the internal PWM
control circuitry. The fast decay portion is defined by:
t_fd = (1 + n) × P_OSC × 8 – P_{OSC ,}
where n = 0 to 15.
For example, with a master oscillator frequency of
4 MHz ( P_OSC = 250 ns), the fixed off-time is adjust-
able from 1.75 to 31.75 μs, in increments of 2 μs. For
t_fd > t_off , the device will effectively operate in fast
decay mode.
D12 – D13 Oscillator Control. 2 bits to set timing
options:
D13
D12
Source and Rate
0
0
Internal clock 4 MHz
0
1
External clock f ÷ 1
1
0
External clock f ÷ 2
1
1
External clock f ÷ 4
A 4 MHz internal oscillator can be used for the tim-
ing functions. If more precise control is required, an
external oscillator can be input to OSC pin. To accom-
modate a wider range of system clocks, an internal
divider is provided to generate the desired MO fre-
quency.
Allegro MicroSystems, Inc.
6
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com