A2550 データシートの表示（PDF） - Allegro MicroSystems
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A2550 Datasheet PDF : 15 Pages
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A2550
Relay Driver with 5 V Regulator
for Automotive Applications
Applications Information
Dropout Voltage
For operation with VBB below the specified range of operat-
ing voltages, use the Pass Transistor On-Resistance RREG5
to determine the maximum allowed regulator current,
IREG5(max). This current is limited by the difference between
VBB and VREG5, according to the following equation:
I < V R− V REG5
BB
REG5
REG5
(1)
Figure 3 shows the results of this condition combined with
the rated regulator current, in normal operation.
Note that, although the regulator is specified for normal
operation with VBB well above normal automotive voltages,
in general thermal constraints will limit maximum opera-
tional VBB.
Fault Logic
The A2550 offers several protection and fault detection
features. The operation of thermal shutdown, watchdog
monitoring of the microcontroller, and regulated voltage
undervoltage lockout are described in the Timing Diagrams
section. The fault logic is described in table 1.
Table 1. Fault Logica
Inputs
Outputs
NPOR
The following faults generate a RESET state:
• watchdog alarm
• VREG5 falls below the UVLO level
In addition, the following conditions cause a low NPOR
signal if the NPOR pin is pulled up by VREG5 (because
these conditions disable VREG5):
• overtemperature (Thermal Shut Down)
• no ENABLE signal (EN = ENBAT = 0)
70
60
50
40
30
20
10
0
0
5
10
15
20
VBB (V)
Figure 3. Current Capability of the 5 V Regulator (VREG5)
Mode of Operation
1
0
0
0
0
1
1
1 INx Normal Operation: OUTx active for INx active.
1
0
0
0
1
1
1
1
Z
OCx disables OUTx only. OUTx latched OFF until INx
removed and reapplied.
1
0
0
1
X
1
1
Pulse
Z
NPOR periodically pulses to attempt RESET of
microcontroller.
1
0
1
X
X
1
1
0
Z
NPOR remains active after UVLO recovers until POR
delay expires.
1
1
X
X
X
1
0
0
Z
0
X
X
X
X
0
0 Off
aX indicates “don’t care,” Z indicates high impedence.
bThis entry is a logical OR of the EN and ENBAT pins.
Z
Sleep mode. NPOR = 0 when pulled up by VREG5
because VREG5 = 0.
Allegro MicroSystems, Inc.
11
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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