Field-Programmable, Chopper-Stabilized,
Unipolar Hall-Effect Switches
A3250
and
A3251
9
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
V
PH
V+
t
V
PM
V
PL
0
T
d(1)
T
d(0)
T
d(P)
Figure 1. Pulse amplitudes and durations
PROGRAMMING PROTOCOL CHARACTERISTICS, T
A
= 25ºC, unless otherwise noted
Characteristic Symbol Test Conditions Min. Typ. Max. Units
Programming Voltage
1
V
PL
Minimum voltage range during programming 4.5 5.0 5.5 V
V
PM
10 11 12 V
V
PH
23 25 26 V
Programming Current
2
I
PP
Maximum supply current during programming – 500 – mA
Pulse Width
t
d(0)
OFF time between programming bits 20 – – s
t
d(1)
Pulse duration (ON time) for enable, address, fuse
blowing or lock bits
20 – – s
t
d(P)
Pulse duration (ON time) for fuse blowing 100 300 – s
Pulse Rise Time t
r
V
PL
to V
PM
;
V
PL
to V
PH
11 – – s
Pulse Fall Time t
f
V
PM
to V
PL
; V
PH
to V
PL
5––s
1
Programming voltages are measured at the VCC pin.
2
A bypass capacitor with a minimum capacitance of 0.1 F must be connected from VCC to the GND pin of the device in order to provide
the current necessary to blow the fuse.
Additional information on device programming and program-
ming products is available on www. allegromicro.com. Program-
ming hardware is available for purchase, and programming
software is available free of charge.
Programming Protocol
The operate switchpoint, B
OP
, can be field-programmed. To do
so, a coded series of voltage pulses through the VCC pin is used
to set bitfields in onboard registers. The effect on the device
output can be monitored, and the registers can be cleared and
set repeatedly until the required B
OP
is achieved. To make the
setting permanent, bitfield-level solid state fuses are blown, and
finally, a device-level fuse is blown, blocking any further cod-
ing. It is not necessary to program the release switchpoint, B
RP
,
because the difference between B
OP
and B
RP
, referred to as the
hysteresis, B
HYS
, is fixed.
The range of values between B
OP(min)
and B
OP(max)
is scaled to
64 increments. The actual change in magnetic flux (G) repre-
sented by each increment is indicated by B
RES
(see the Operating
Characteristics table; however, testing is the only method for
verifying the resulting B
OP
). For programming, the 64 incre-
ments are individually identified using 6 data bits, which are
physically represented by 6 bitfields in the onboard registers.
By setting these bitfields, the corresponding calibration value is
programmed into the device.
Three voltage levels are used in programming the device: a low
voltage, V
PL
, a minimum required to sustain register settings; a
mid-level voltage, V
PM
, used to increment the address counter
in the device; and a high voltage, V
PH
, used to separate sets of
V
PM
pulses (when short in duration) and to blow fuses (when
long in duration). A fourth voltage level, essentially 0 V, is used
to clear the registers between pulse sequences. The pulse values
are shown in the Programming Protocol Characteristics table and
in figure 1.
Code Programming. Each bitfield must be individually set. To
do so, a pulse sequence must be transmitted for each bitfield that
is being set to 1. If more than one bitfield is being set to 1, all
pulse sequences must be sent, one after the other, without allow-
ing V
CC
to fall to zero (which clears the registers).
The same pulse sequence is used to provisionally set bitfields as
is used to permanently set bitfield-level fuses. The only differ-
ence is that when provisionally setting bitfields, no fuse-blowing
pulse is sent at the end of the pulse sequence.
