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PDF A1698 Data sheet ( Hoja de datos )
| Número de pieza | A1698 | |
| Descripción | High Accuracy Sensor IC | |
| Fabricantes | Allegro Micro Systems | |
| Logotipo |  |
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A1698
Two-Wire, True Zero-Speed, High Accuracy
Sensor IC with Speed and Direction Output
FEATURES AND BENEFITS
• Integrated capacitor for EMC suppression in a single
overmolded miniature package
• Wide leads facilitate ease of assembly
• True zero-speed operation
• Pulse-width output protocol
• Automatic Gain Control (AGC) for air gap independent
switchpoints
• Automatic Offset Adjustment (AOA) for signal
processing optimization, providing large operating air
gap range
• Single chip sensing IC for high reliability
• Fully synchronous digital logic with Scan and IDDQ
testing
Package: 2-pin SIP (suffix UB)
DESCRIPTION
The A1698 is a Hall-effect-based integrated circuit (IC) that
provides a user-friendly solution for two-wire speed sensing of
ring magnets or ferrous targets (when back-biased by the user)
down to zero-speed in applications where speed and direction
is required. The A1698 is offered in the UB package, which
integrates the IC and a high temperature ceramic capacitor in
a single overmolded SIP package. The integrated capacitor
provides enhanced EMC performance.
The integrated circuit incorporates Hall-effect circuits and signal
processing that switches in response to differential magnetic
signals created by magnetic encoders, or, when properly back-
biased with a magnet, from ferromagnetic targets. The circuitry
contains a sophisticated digital circuit that reduces magnet
and system offsets, calibrates the gain for air gap independent
switchpoints, and provides true zero-speed operation.
The regulated current output is configured for two-wire interface
circuitry and is ideally suited for obtaining speed and direction
information in wheel speed applications.The 2-pin SIP package
is lead (Pb) free, with tin leadframe plating.
Not to scale
1
SUPPLY
Internal Regulator
Offset Gain
Adjust Adjust
Amp
Chopper
Stabilization
Amp
Offset Gain
Adjust Adjust
Filter
ADC
Filter
ADC
Digital
Controller
Output
Control
GROUND
2
A1698-DS, Rev. 2
Functional Block Diagram
1 page  
A1698
Two-Wire, True Zero-Speed, High Accuracy
Sensor IC with Speed and Direction Output
1
A1698
CSUPPLY
2
RL
100 Ω
CL
VSUPPLY
Figure 1: Typical Application Circuit
BSEQ(n)
BSEQ(n+1)
Figure 2: Differential Signal Variation
Target
S
VPROC
NS
TTARGET
TVPROC
N
VPROC = the processed analog signal of the sinusoidal
magnetic input (per channel)
TTARGET = the period between successive sensed target
magnetic edges of the same polarity (either
both north-to-south or both south-to-north)
Figure 3: Definition of TTARGET
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
5 Page 
A1698
Two-Wire, True Zero-Speed, High Accuracy
Sensor IC with Speed and Direction Output
POWER DERATING
The device must be operated below the maximum junction
temperature of the device (TJ(max)). Under certain combinations
of peak conditions, reliable operation may require derating
supplied power or improving the heat dissipation properties of
the application. This section presents a procedure for correlating
factors affecting operating TJ. (Thermal data is also available on
the Allegro MicroSystems website.)
The Package Thermal Resistance (RθJA) is a figure of merit sum-
marizing the ability of the application and the device to dissipate
heat from the junction (die), through all paths to the ambient air.
Its primary component is the Effective Thermal Conductivity
(K) of the printed circuit board, including adjacent devices and
traces. Radiation from the die through the device case (RθJC )
is relatively small component of RθJA. Ambient air temperature
(TA ) and air motion are significant external factors, damped by
overmolding.
The effect of varying power levels (Power Dissipation or PD), can
be estimated. The following formulas represent the fundamental
relationships used to estimate TJ, at PD.
×PD = VIN IIN
(1)
ΔT = PD × RθJA
(2)
TJ = TA + ΔT
(3)
For example, given common conditions such as: TA= 25°C,
VCC = 12 V, ICC = 14 mA, and RθJA = 213 °C/W, then:
PD = VCC × ICC = 12 V × 7 mA = 84 mW
ΔT = PD × RθJA = 84 mW × 213 °C/W = 17.9°C
TJ = TA + ΔT = 25°C + 17.9°C = 42.9°C
A worst-case estimate, PD(max), represents the maximum allow-
able power level (VCC(max), ICC(max)), without exceeding TJ(max),
at a selected RθJA and TA.
Example: Reliability for VCC at TA = 150°C, package UB, using
minimum-K PCB.
Observe the worst-case ratings for the device, specifically:
RθJA = 213°C/W, TJ(max) = 165°C, VCC(max) = 24 V, and
ICC(AVG) = 14.66 mA. ICC(AVG) is computed using ICC(HIGH)(max)
and ICC(LOW)(max), with a duty cycle of 73% computed from
tw(REV)(max) on-time and tw(FW)(min) off-time (pulse width proto-
col). This condition happens at a select limiting frequency.
Calculate the maximum allowable power level (PD(max) ). First,
invert equation 3:
ΔTmax = TJ(max) – TA = 165 °C – 150 °C = 15 °C
This provides the allowable increase to TJ resulting from internal
power dissipation. Then, invert equation 2:
PD(max) = ΔTmax ÷ RθJA = 15°C ÷ 213 °C/W = 70.4 mW
Finally, invert equation 1 with respect to voltage:
VCC(est) = PD(max) ÷ ICC(AVG) = 70.4 mW ÷ 14.6 mA = 4.8 V
The result indicates that, at TA, the application and device can
dissipate adequate amounts of heat at voltages ≤VCC(est).
Compare VCC(est) to VCC(max). If VCC(est) ≤ VCC(max), then reliable
operation between VCC(est) and VCC(max) requires enhanced
RθJA. If VCC(est) ≥ VCC(max), then operation between VCC(est) and
VCC(max) is reliable under these conditions.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet A1698.PDF ] | |
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