A2550KLP-T Allegro Microsystems Inc, A2550KLP-T Datasheet - Page 12

• Manufacturer Part Number: A2550KLP-T
• Manufacturer: Allegro Microsystems Inc

Specifications of A2550KLP-T

• Lead Free Status / RoHS Status: Compliant

A2550
NPOR is pulsed for a watchdog fault. For the remaining
faults, NPOR is held low for the duration of the fault. After
the fault condition is removed, NPOR remains low during
the t
capacitor fed by a current source at the CPOR pin, according
to the following formula:
The scaling factor is simply derived from the specifications
using the typical value of I
Watchdog
The watchdog monitors the microcontroller to detect if
it locks up. To do so, the watchdog checks for pulses on
the Watchdog Input pin (WDI), and if they are absent for
longer than the timeout period, t
NPOR, which pulses periodically. t
the external capacitor fed by a current source at the CWD
pin. The voltage change is 1 V, so using the typical value of
I
The pulse width for NPOR active, t
tionally to the value of the external capacitor at the CWD
pin. Using the typical value of I
See the specification tables for tolerances.
When not used, disable watchdog by tying WDI to NPOR
and tying CWD low. Table 2 shows watchdog timing for the
nominal capacitances listed.
CWD
POR
(charging) we have:
Table 2. Timing Set by Capacitors
period. The latter is set by the value of the external
(μF)
0.22
0.47
0.1
C
1
C
t
t
t
t
WD
POR
WDR
POR
POR
(ms)
t
200
POR
20
44
94
200
200
14
V
POR
REF
µF
ms
µF
ms
µF
ms
:
CWD
I
WD
POR
(ms)
V
200
t
20
44
94
WD
TRIP(L)
WD
WDR
, the watchdog activates
C
(discharging) we have:
C
C
POR
WD
WD
is proportional to
, also scales propor-
Applications Information
t
(ms)
WDR
14
1
3
7
(2)
(3)
(4)
(5)
Output Overcurrent
When the OC (overcurrent) protection is triggered in a
driver, that driver is disabled for self-protection. No other
functions are affected; NPOR and VREG5 operate nor-
mally. A disabled output driver remains shut down until the
respective INx is brought low, then high again; at which time
OUTx turns on. OUTx will switch on again the next time
INx is applied. If a short-to-battery still exists, the overcur-
rent will trip each time INx is reapplied.
Sleep
The A2550 is put to sleep by holding both EN and ENBAT
low. In sleep mode all functions are shut down, including
VREG5. If the VREG5 regulator is required at all times, dis-
able sleep mode by tying ENBAT to VBB.
Power Limits
Power dissipation, P
maximum allowed power dissipation, P
the formula:
The maximum junction temperature, T
resistance, R
The three main contributors to power dissipation are:
For example, to determine if T
given:
• P
• P
• P
Relay Driver with 5 V Regulator
P
P
BIAS
REG
LS
R
BIAS
REG
θJA
T
from low-side driver conduction
A
from the linear regulator voltage drop
from the supply bias current
= 55°C/W , and
= 125°C ; and
= V
= 14 V × 3 mA = 42 mW , and
= (V
= (14 V – 4.9 V) × 20 mA= 182 mW , and
for Automotive Applications
BB
T =
θJA
BB
J
× I
, are given in the specification tables.
– V
(P
BBQ
D(max)
REG5(min)
D
, is limited by thermal constraints. The
R
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Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
θJA
) × I
J
+
is in an acceptable range,
T
REG5
A
) ≤
T
J(max)
J(max)
D(max)
, and the thermal
, is found from
(6)
(7)
(8)
12