A6850
Dual Channel Switch Interface IC
Not for New Design
These parts are in production but have been determined to be NOT FOR
NEW DESIGN. This classification indicates that sale of this device is
currently restricted to existing customer applications. The device should
not be purchased for new design applications because obsolescence in
the near future is probable. Samples are no longer available.
Date of status change: October 1, 2022
Recommended Substitutions:
For existing customer transition, and for new customers or new applications, contact factory.
NOTE: For detailed information on purchasing options, contact your
local Allegro field applications engineer or sales representative.
Allegro MicroSystems reserves the right to make, from time to time, revisions to the anticipated product life cycle plan for a
product to accommodate changes in production capabilities, alternative product availabilities, or market demand. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems assumes no responsibility for
its use; nor for any infringements of patents or other rights of third parties which may result from its use.
A6850
Dual Channel Switch Interface IC
FEATURES AND BENEFITS
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DESCRIPTION
4.75 to 26.5 V operation
Low VIN-to-VOUT voltage drop
1/ current sense feedback
10
Survive short-to-battery and short-to-ground faults
Survive 40 V load dump
>4 kV ESD rating on the output pins, >2 kV on all other pins
Output current limiting
Low operating and Sleep mode currents
Integrates with Allegro A114x and A118x Hall effect
two-wire sensor ICs
The Allegro™ A6850 is designed to interface between a
microprocessor and a pair of 2-wire Hall effect sensor ICs.
The A6850 uses protected high-side low resistance DMOS
MOSFETs to switch the supply voltage to the two Hall effect
devices. Each switch can be controlled independently via
individual ENABLE pins and both switches are protected
with current-limiting circuitry. The output switches are rated
to operate to 26.5 V and will source at least 25 mA per channel
before current limiting.
Typical two-wire Hall device applications require the user to
measure the supply current to determine whether the Hall IC
is switched on (magnetic field present) or switched off (no
magnetic field present). This is usually accomplished by using
an external series shunt resistor and protection circuits for the
microprocessor. In many systems, the sensed voltage is used
as the input to a microprocessor analog-to-digital (A-to-D)
input. This provides the system with an indication of the status
of the two-wire switch as well as provides the capability for
diagnostic information if there is an open or shorted Hall device.
PACKAGE: 8-pin SOIC (suffix L)
Approximate Footprint
Continued on the next page…
Functional Block Diagram
VIN
ENABLE1
Control
Block
ENABLE2
SENSE1
× IOUTPUT1
1/
10
Fault
Detection
OUTPUT1
Fault
Detection
OUTPUT2
SENSE2
× IOUTPUT2
1/
10
GROUND
6850-DS, Rev. 8
MCO-0000882
October 1, 2022
A6850
Dual Channel Switch Interface IC
Description (continued)
The A6850 eliminates the need for the external series shunt resistor
in Hall device applications by incorporating an integrated current
mirror which reports the Hall IC supply current as a 1/10 value on
the SENSE1 or SENSE2 output pin. A low current Sleep mode is
Selection Guide
Part Number
available ( 7 V
VIN < 7 V
–
4.0
7.5
µs
–
–
–
–
35
–20
Ω
µA
–100
–
100
µA
–
0
0
2.0
–
125
–
–
–25.0
–
–
–
–
–
–
40
8.0
–35.0
10
6
VIN – 1
–
0.4
375
100
20
–45.0
µA
V
V
V
V
mV
µA
µA
mA
–
500
750
µA
27.0
–
–
–
–
2.0
175
15
33.0
–
–
–
V
V
°C
°C
Enable Delay Time2
tENdlyLH
Disable Delay Time2
tENdlyHL
OUTPUTx Source Resistance
OUTPUTx Leakage Current
SENSEx Output Current Offset3
SENSEx Voltage4
ENABLEx Input Voltage Range
ENABLEx Input Hysteresis
ENABLEx Current
OUTPUT Current Limit
OUTPUT Reverse Bias Current
Overvoltage Protection Threshold
Overvoltage Protection Hysteresis
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
1Delay
2R
ISENSE(ofs)
ISENSEQ
VSENSEx
VENABLEH
VENABLEL
VENABLEhys
IENABLE
IOUTPUTM
IOUTPUT(rvrs)
VOVP
VOVPhys
TTSD
TTSDhys
At least one output enabled
ENABLEx = 2.0 V
ENABLEx = 0.4 V
Reverse bias blocking: VIN = 4.75 V,
VOUTPUT = 26.5 V
Rising VIN
Temperature Increasing
from end of Sleep mode to outputs enabled.
SENSEx
3For
RDS(on)
IOUTPUTQ
= 1.5 kΩ.
input and output current specifications, negative current is defined as coming out of (sourced from) the specified device pin.
4User to ensure that V
SENSEx remains within the specified range. If VSENSEx exceeds the maximum value, the device is self-protected by an
internal clamp, but not all parameters perform as specified.
Allegro MicroSystems
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3
A6850
Dual Channel Switch Interface IC
Characteristic Performance
0 mA
OUTPUTx
current
10%
90%
– 10 mA
trLH
tfHL
90%
SENSEx
voltage
10%
0V
Figure 1. Signal Channel Timing, ENABLE1 = ENABLE1 = High, RSENSE = 1.5 kΩ
50%
ENABLEx
Voltage
0V
0 mA
OUTPUTx
Current
tENdlyHL
tENdlyLH
50%
SENSEx
Voltage
0V
Figure 2. Enable Delays, one ENABLE input held high to prevent the IC going into Sleep mode
Allegro MicroSystems
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A6850
Dual Channel Switch Interface IC
Functional Description
SENSE Pin Outputs
The A6850 divides the OUTPUTx pin current by 10 and mirrors
it onto the corresponding SENSEx pin. Putting sense resistors,
RSENSE , from these pins to ground will create a voltage that
can be read by an ADC (analog-to-digital converter). The value
of RSENSE should be chosen so that the voltage drop across the
sense resistor (VRSENSE) does not exceed the maximum voltage
rating of the ADC. For further protection of the ADC, an external
clamping circuit, such as a Zener diode, can be used to clamp any
transient current spikes that may occur on the output that would
be translated onto the SENSE pins.
Overvoltage Protection
The A6850 has built-in overvoltage protection against a load
dump on the supply bus. In the case of a load dump, or when VIN
is connected to the battery supply bus and VIN rises above the
overvoltage threshold, VOVP , the A6850 will shut off the outputs.
The sense current is one tenth of the output current, plus an offset
current. This offset current is consistent across the whole range
of the output current. The sense current can be calculated by the
following formula:
When enabling an output, the part must first come out of sleep
mode. Consequently, the wake-up time amounts to a propagation
delay before the outputs turn on. Also, the ENABLE pins do not
switch with hysteresis until the regulators stabilize.
ISENSEx = (IOUTPUTx / 10) + ISENSE(ofs) .
(1)
The sense resistor must also be chosen to meet the voltage limits
on the sense pin (see Electrical Characteristics table).
Sleep Mode
Low-leakage or sleep modes are required in automotive applications to minimize battery drain when the vehicle is parked. The
A6850 enters sleep mode when both ENABLE pins are low. In
sleep mode, the internal regulators and all other internal circuitry
are disabled.
After the internal regulators stabilize, internal circuitry is enabled
and the outputs turn on, as shown in figure 3. As long as one
ENABLE pin is held high, the A6850 operates with hysteresis.
Output Current Limit
The A6850 limits the output current to a maximum current of
IOUTPUTM. The output current will remain at the current limit
until the output load is reduced or the A6850 goes into thermal
shutdown.
The high output current limit allows the bypass capacitor, CBYP ,
on the Hall sensor IC to charge up quickly. This allows a high slew
rate on the VCC pin of the Hall sensor IC, ensuring that the sensor
IC Power-On State will be correct. See the Applications Information section for schematic diagrams and power calculations.
Output Faults
The A6850 withstands short-to-ground or short-to-battery of the
OUTPUTx pins. In the case of short-to-ground, current is held to
the current limit (IOUTPUTM).
If VOUTPUTx > (VIN + 0.7 V) during a short-to-battery event, the
A6850 monitors VOUTPUTx and disables the outputs. Because the
protection circuitry requires a finite amount of time to disable the
outputs, a bypass capacitor of 1 µF is necessary on VIN. Although
OUTPUTx sinks current into the A6850 in this state, the reverse
current is shunted to ground and does not appear on the VIN pin.
ENABLE
VENABLEL
> tON
RegOk
VREG
OUTPUT
Figure 3. Activation Timing Diagram. Exiting Sleep mode via ENABLE
signal to output waveform.
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5
A6850
Dual Channel Switch Interface IC
Signal and Enable delays
When ENABLEx = 1, current signals applied to the OUTPUTx
pins will appear scaled and delayed on the SENSEx pins. The
transfer characteristic can be considered that of a low pass filter.
The response time definitions are given in figures 1 and 2, in the
Characteristic Performance section.
The rise time response is dependent on the effective capacitance
loading on the SENSEx pin.
The RC time constant, τ, can be estimated using:
τ = RSENSEx (90 + CSENSE) (2)
where RSENSEx is in kΩ and CSENSE is in pF; the result will
be in ns.
The 10% to 90% rise time, trLH , may be estimated from:
trLH = 2.2 × τ (3)
When a capacitor is added in parallel with the signal source connected to an OUTPUTx pin, additional allowance must be made
for settling time caused by the inrush current needed to recharge a
partially, or fully discharged, capacitor which has decayed during
the disabled period.
During this time the current required may reach IOUTPUTM, the
current limit value for the OUTPUTx pins.
The effects will be most noticeable on a SENSEx pin and will
usually cause a signal overshoot as shown as tENsettle in figure 4.
Thermal Shutdown (TSD)
The A6850 protects itself from excessive heat damage by
disabling both outputs when the junction temperature, TJ , rises
above the TSD threshold (TTSD). The outputs will remain off
until the junction temperature falls below the TTSD level minus
the TSD hysteresis, TTSDhys.
The small signal low pass filter bandwidth based on a single pole
response may be estimated using:
BW = 350 / trLH
(4)
The result is in MHz when trLH is in ns.
If the values of trLH and tfHL are significantly different then a better estimate may be given by:
BW = 700 / (trLH + tfHL ) (5)
The result is in MHz when trLH and tfHL are in ns.
Each signal channel may be enabled or disabled individually via
their respective ENABLEx pins, as shown in table 1.
ENABLEx
50%
0 mA
OUTPUTx
tENdlyLH
Table 1. Enable/Disable Signal Channel Truth Table
EN1
EN2
IOU1
IOU2
SEN1
SEN2
L*
L*
0
0
0
0
H
L
I1
0
I1 / 10
0
L
H
0
I2
0
I2 / 10
H
H
I1
I2
I1 / 10
I2 / 10
*Sleep mode
SENSEx
tENsettle
0V
Figure 4. Overshoot resulting from additional capacitance.
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A6850
Dual Channel Switch Interface IC
TJ can be estimated by calculating the power dissipation (PD) of
the A6850. To calculate PD:
Example: Calculating the power dissipation and temperature rise,
given:
TA = 25°C ,
PD = VIN IINQ (6)
– VOUTPUT1 IOUTPUT1 – VOUTPUT2 IOUTPUT2
IINQ = 5 mA ,
– VSENSE1 ISENSE1 – VSENSE2 ISENSE2 .
PD = VIN IINQ
VIN = 5 V ,
(7)
IOUTPUT1 = IOUTPUT2 = 15 mA ,
ISENSEx = IOUTPUTx /10 = 1.5 mA ,
+ (VIN – VOUTPUT1 ) IOUTPUT1
RSENSE1 = RSENSE2 = 2 kΩ , and
+ (VIN – VOUTPUT2 ) IOUTPUT2
+ (VIN – VSENSE1) ISENSE1
+ (VIN – VSENSE2) ISENSE2 .
Then:
PD = 5 V × 5 mA
When IOUTPUTx × RDS(on) < approximately 700 mV, then:
+ 0.525 V×15 mA+[5 V – (1.5 mA×2 kΩ)]×1.5 mA
(VIN – VOUTPUTx ) = IOUTPUTx × RDS(on) .
+ 0.525 V×15 mA+[5 V – (1.5 mA×2 kΩ)]×1.5 mA
When IOUTPUTx × RDS(on) > approximately 700 mV, then:
IOUTPUTx = IOUTPUT (max) ,
and VOUTPUTx is set by the loading on the OUTPUTx pin.
The temperature rise of the A6850 can be calculated by multiplying PD and the thermal resistance from junction to ambient, RθJA .
The formula for temperature rise, ∆T, is:
∆T = PD × RθJA .
IOUTPUTx × RDS(on) = 15 × 35 = 525 mV = VIN – VOUTPUTx .
(8)
The RθJA for an 8-pin SOIC (Allegro L package) on a one-layer
board with minimum copper area is 140 °C/W. (More thermal
data is available on the Allegro MicroSystems website.)
= 46.75 mW .
Substituting in equation 8:
∆T = 46.75 mW × 140 °C/W = 6.5°C .
Substituting in equation 9:
TJ = 25°C + 6.5°C = 31.5°C .
The total junction temperature can be calculated by:
TJ = TA + ∆T ,
(9)
where TA is the ambient air temperature.
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
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A6850
Dual Channel Switch Interface IC
Applications Information
Two-Wire Hall IC Interfacing
When voltage is applied to two-wire Hall effect ICs, current
flows within one of two narrow ranges. Any current level not
within these ranges indicates a fault condition.
The following table describes some of the possible output
conditions that can be monitored through the SENSE pins.
Figure 5 is a typical application using the A6850 with dual
Hall effect ICs.
Signal and Fault Table
Output Pin Current
(mA)
Sense Pin Current
(mA)
Sense Pin Voltage,
Rsense= 1.5 kΩ
(V)
OUTPUT Pin Short-to-Ground
25 to 45
2.5 to 4.5
3.75 to 6.75
Logic High from Hall IC
12 to 17
1.2 to 1.7
1.8 to 2.55
0.0
0.0
0
2 to 6.9
0.2 to 0.69
0.3 to 1.04
Thermal Shutdown
0.0
0.0
0
OUTPUT Pin Open
0.0
0.0
0
Condition
Short-to-Battery
Logic Low from Hall
*This
IC*
current range includes all A114x and A118x devices.
VCC or
VBAT
VCC
VIN
Digital Output
Digital Output
1 µF
1
ENABLE1
3
ENABLE2
5
VIN
OUTPUT1
8
CBYP
0.01 µF
A6850
Controller
ADC
ADC
2
SENSE1
4
SENSE2
Wiring Harness
OUTPUT2
6
A114x or
A118x
GROUND
RSENSE1
1.5 kΩ
RSENSE2
1.5 kΩ
CBYP
0.01 µF
7
A114x or
A118x
Figure 5. Typical Application with 2-Wire Hall Effect ICs
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A6850
Dual Channel Switch Interface IC
Mechanical Switch Interfacing
A series resistor included in the circuit reduces power dis-
The A6850 can be used as an interface between mechanical
switches, set in a switch-to-ground configuration, and a low
voltage microprocessor. A series resistor must be placed in
the circuit to limit current when the mechanical switch is
closed, in order to prevent excessive power dissipation in the
A6850.
sipation in the OUTPUTx section of the A6850.
For example, to calculate the power dissipation in the A6850
driving two mechanical switches with 1 kΩ series resistors,
with VIN = 12 V, assume that the current limit for each of
the outputs is set to the maximum value, IOUTPUTM (max) =
45 mA.
When the mechanical switch is closed without a series resistor, the A6850 will be at the current limit. The full 12 V of the
power supply will drop across the A6850 at 45mA The power
dissipation for one mechanical switch closed would be:
PD1 = VDrop1 × IOUTPUT1
= 12 V × 45 mA
= 540 mW
(6)
VCC or
VBAT
VCC
VIN
Digital Output
Digital Output
The current is then limited to:
IOUTPUT1 = VIN / (35 + RSERIES)
= 12 V / 1035 Ω
= 11.59 mA
(7)
VDrop1 = 35 × IOUTPUT1
(8)
= 405.7 mV
The power dissipation in the A6850 from this switch is much
lower:
PD1 = VDrop1 × IOUTPUT1
= 0.4057 V × 11.3 mA
= 4.58 mW
1 µF
1
ENABLE1
3
ENABLE2
5
VIN
OUTPUT1
8
(9)
Wiring Harness
RSERIES
A6850
Controller
Input1
Input2
2
SENSE1
4
SENSE2
OUTPUT2
GROUND
RSENSE1
RSENSE2
6
RSERIES
7
Figure 6. Typical Application with Mechanical Switches
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A6850
Dual Channel Switch Interface IC
Ganging SENSE1 and SENSE2
and ENABLE2 may be activated simultaneously, with the
In certain applications both outputs may be read with a
single ADC channel. The OUTPUTx loads are enabled by
alternatively activating ENABLEx. In fact, both ENABLE1
SENSE1 and SENSE2 currents added together. For valid
measurements the load resistor need only be selected so that
VSENSEx remain within specification.
Vin
Digital Output
Digital Output
1 µF
Enable 1
Enable 2
Controller
Vin
Output 1
LOAD1
Vcc
or
Vbat
Vcc
A6850
Sense 1
Sense 2
ADC
Output 2
LOAD2
R
Figure 7. Outline of ganged configuration
VENABLE1
VENABLE2
IOUTPUT1
ILOAD1
ILOAD2
IOUTPUT2
VADC
ILOAD1
R×ILOAD1/10
ILOAD2
R×ILOAD2/10
R× (ILOAD1/10 + ILOAD2/10)
Figure 8. Functional response in ganged configuration
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A6850
Dual Channel Switch Interface IC
Protection from EMI
Transients generated by electromagnetic interference (EMI)
can disturb operation of the A6850 or add unwanted noise to the
signals being processed.
The scheme shown in figure 9 illustrates possible supply decoupling and signal filtering options. The selection of protection and
filtering component values will depend on the details of the final
application.
The A6850 must be protected with a suitable bypass capacitor to
prevent transients entering VIN. The capacitor should be as close
to the VIN and GND pins as feasible.
A pi-filter placed between the OUTPUTx pins and the sensor IC
has been shown to demonstrate excellent performance in normal automotive Bulk Cable Injection (BCI) testing. However,
component selection and layout as well as cable specification and
placement must be tailored to the individual application. EMC
results should be validated.
1 µF
VIN
OUTPUT1
ENABLE1
1000 pF
ENABLE2
VBAT
A6850
SENSE1
SENSE2
100 Ω
1
0.1 µF
Hall
Device
2
OUTPUT2
GROUND
Figure 9. Decoupling and filtering suggestions
Allegro MicroSystems
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11
A6850
Dual Channel Switch Interface IC
L Package, 8-Pin SOIC
For Reference Only; not for tooling use
(reference Allegro DWG-0000385, Rev. 2 or JEDEC MS-012AA)
Dimensions in millimeters – Not to scale
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
4.90 BSC
8°
0°
8
0.65
1.27
8
0.21 ±0.04
3.90 BSC
Pin 1 Mark Area
1
6.00 BSC
1.75
2
0.84 +0.43
–0.44
Branded Face
C
8×
0.10 C
0.41 ±0.10
1.27 BSC
5.60
SEATING
PLANE
+0.13
1.62 –0.27
0.15 +0.10
–0.05
0.25 BSC
SEATING PLANE
GAUGE PLANE
1
2
PCB Layout Reference View
Reference land pattern layout
(reference IPC7351 SOIC127P600X175-8M);
all pads a minimum of 0.20 mm from all adjacent pads;
adjust as necessary to meet application process
requirements and PCB layout tolerances.
Allegro MicroSystems
955 Perimeter Road
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12
A6850
Dual Channel Switch Interface IC
Revision Table
Number
Date
6
May 29, 2020
Description
Minor editorial updates
7
June 4, 2021
Updated Package Outline Drawing
8
October 1, 2022
Changed product status: Not for new design
Copyright 2022, Allegro MicroSystems.
Allegro MicroSystems reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit
improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the
information being relied upon is current.
Allegro’s products are not to be used in any devices or systems, including but not limited to life support devices or systems, in which a failure of
Allegro’s product can reasonably be expected to cause bodily harm.
The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems assumes no responsibility for its use; nor
for any infringement of patents or other rights of third parties which may result from its use.
Copies of this document are considered uncontrolled documents.
For the latest version of this document, visit our website:
www.allegromicro.com
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