A1351
High Precision Linear Hall Effect Sensor IC
with a Push/Pull, Pulse Width Modulated Output
19
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Programming State Machine
Initial State
After system power-up, the programming logic is reset to a
known state. This is referred to as the Initial state. All the bit field
locations that have intact fuses are set to logic 0. While in the
Initial state, any V
PM
pulses on the PWMOUT pin are ignored.
To enter the Parameter Selection state, apply a single V
PH
pulse
on the PWMOUT pin.
Parameter Selection State
This state allows the selection of the parameter register con-
taining the bit fields to be programmed. To select a parameter
register, increment through the keys by sending V
PM
pulses on
the PWMOUT pin. Register keys select among the following
programming parameters:
1 pulse Sens / Coarse D
(Q)
2 pulses D
(Q)
3 pulses PWM Frequency / Calibration Test Mode
5 pulses LOCK
Bit Field Addressing State
To enter the Bit Field Addressing state, apply one V
PH
pulse on
the PWMOUT pin. This state allows the selection of the individ-
ual bit fields to be programmed in the selected parameter register
(see the Programming Logic table). To leave this state, either
cycle device power or blow the fuses for the selected code.
Note: Merely addressing the bit field does not permanently set
the value of the selected programming parameter; fuses must be
blown to do so.
Fuse Blowing State
To blow an addressed bit field, apply a V
PH
pulse on the PWM-
OUT pin. Power to the device should then be cycled before
additional programming is attempted.
Note: Each bit representing a decimal code must be blown indi-
vidually (see the Fuse Blowing section).
Power-up
Initial
Parameter Selection
Bit Field Addressing
Sens/
Coarse
D
(Q)
D(Q)
(Fine)
V
PH
V
PM
V
PH
V
PH
V
PH
V
PH
V
PH
V
PH
V
PH
V
PH
V
PH
V
PH
V
PM
[Key sequence]
[Code sequence]
V
PM
V
PM
V
PM
V
PM
V
PM
1
2
Null
Lock
V
PM
V
PM
V
PM
V
PM
f
PWM
/
Calibration
Test Mode
2
n
1
n= bits in
register
Fuse Blowing
User Power-down
Required
V
PM
= V
P(LOW)
?V
P(MID)
?V
P(LOW)
V
PH
= V
P(LOW)
?V
P(HIGH)
?V
P(LOW)