A2550 Datasheet

A2550
Relay Driver with 5 V Regulator
for Automotive Applications
Features and Benefits
Description
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Large numbers of relay-based applications require the use of a
microprocessor which implements complex system control. In
these systems, there is the need for microprocessor logic supply
voltage, power-on reset circuitry, and watchdog capabilities. The
Allegro™ A2550 combines the functions of voltage regulator,
watchdog, and reset, as well as three low-side DMOS relay
driver outputs. Primarily targeted at automotive applications,
this IC is designed to provide robust performance over extended
voltage and temperature ranges.
Three independent low-side DMOS output drivers
Short-circuit protection of drivers
Eliminates need for flyback diodes on relays
Thermal shutdown
Separate precision 5 V regulator (2%)
Current clamp on 5 V regulator
16-pin TSSOP package with exposed thermal pad
Programmable reset (NPOR) delay time
Programmable watchdog
Automotive voltage and temperature ranges
Active clamps for automotive load dump specifications
Lead (Pb) free
Three low-side DMOS drivers can drive inductive loads, such
as relay coils. Each driver integrates rugged voltage clamps
which survive automotive load dump pulses up to 48 V. The
40 V rating on VBB also ensures adequate survival in harsh
automotive environments.
Package: 16 pin TSSOP (suffix LP) with
exposed pad
A 5 V linear regulator provides 40 mA of output current, with
a tolerance of 2% over the operating temperature range. To
enhance the usefulness of the IC in automotive applications,
the 5 V regulator output, as well as the three low-side driver
outputs are protected against overcurrent conditions.
Continued on the next page…
Approximate Scale
Typical Application
1
2
System
Logic
3
4
5
6
7
8
IN1
OUT1
IN2
OUT2
IN3
OUT3
PGND
NPOR
CWD
WDI
CPOR
EN
ENBAT
VREG5
0.47 μF
X7R
2550-DS, Rev. 4
A2550
LGND
VBB
16
15
14
13
12
11
10
9
Relays or other
inductive loads
Relay Driver with 5 V Regulator
for Automotive Applications
A2550
Description (continued)
The A2550 also includes power-on reset circuitry (NPOR) as well as
an integrated watchdog circuit. Combined, they service the monitoring
and reset requirements of a system microprocessor.
The A2550 is supplied in a 16-pin TSSOP package with exposed
thermal pad (package LP).The package is lead (Pb) free, with 100%
matte tin leadframe plating.
Selection Guide
Part Number
A2550KLPTR-T
Packing
13-in. reel, 4000 pieces / reel
Absolute Maximum Ratings
Characteristic
Supply Voltage
High Voltage Enable
Output Driver
Output Load Clamp
Symbol
Notes
VBB
VENBAT
VOUT
VOUT(CL)
Continuous rating; outputs off
Rating
Units
–0.3 to 60
V
–0.3 to 60
V
–1.4 to 48
V
Transient rating
60
V
Maximum Energy at Outputs
EOUT
Single Pulse, TJ(initial) = 125°C
100
mJ
Peak Power Dissipation at Outputs
PPK
Single pulse, TJ(initial) = 125°C, ∆t = 1 ms; see
figure 2 for different durations and TJ(initial)
1.7
W
–0.3 to 7
V
All other pins
ESD Rating – Human Body Model
AEC-Q100-002; all pins
2.5
kV
ESD Rating – Charged Device Model
AEC-Q100-011; all pins
1050
V
Operating Ambient Temperature
TA
–40 to 125
ºC
Maximum Junction Temperature
TJ (max)
150
ºC
Tstg
–55 to 150
ºC
Storage Temperature
Range K
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
Relay Driver with 5 V Regulator
for Automotive Applications
A2550
Functional Block Diagram
CBB
Hi-V
Enable
VBB
VBAT
A2550
ENBAT
Hi-V
Protection
TSD
VREG5
5V
Linear
Regulator
CREG5
0.47 μF
X7R
Enable
Internal
Reference
Vref
EN
Adjustable
Delay
NPOR
CPOR
Vdc
PGND
Relays or Other
Inductive Loads
VREG5 UVLO
TSD
A
LGND
CWD
WDI
Watchdog
Coil 1
Coil 2
Coil 3
OUT1
Micro
Controller
IN1
Overcurrent
Protection
200 k7
OUT2
IN2
Overcurrent
Protection
200 k7
OUT3
IN3
Overcurrent
Protection
200 k7
Fault
Logic
A
LGND and PGND must be connected externally.
Component Selection Table
Name
Suitable Characteristics
CBB
CREG5
CWD, CPOR
33 μF, 63 V electrolytic
0.47 μF, 25 V, X7R ceramic
0.22 μF, 16 V, X7R ceramic
Representative Device
United Chemi-Con EGXE630E--330MH12D
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A2550
Relay Driver with 5 V Regulator
for Automotive Applications
ELECTRICAL CHARACTERISTICS, –40°C ≤ TJ ≤ 150°C, VBB within operating limits, unless otherwise noted
Characteristics
Symbol
Test Conditions
Min.
Supply
VBB Operating Voltage1
VBB
7
All OUTx Off; EN = 5 V, VBB = ENBAT = 14 V
–
IBBQ
IBB
VBB Supply Current
All OUTx On; EN = 5 V, VBB = ENBAT= 14 V
–
IBBS
Sleep mode, EN = ENBAT = 0
–
Logic Inputs
HIGH input level
3.5
ENBAT Input Voltage2
VENBAT
LOW input level
0
HIGH input level
3.5
VIH
EN, WDI, and INx Input Voltage
VIL
LOW input level
0
ENBAT, EN, WDI, INx Input Voltage
VIhys
200
Hysteresis
HIGH input level, VBB = VBB(max)
–
ENBAT Input Current2,3
HIGH input level, VBB = 14 V
IENBAT
–
LOW input level
–50
HIGH input level
–
EN Input Current2
IEN
LOW input level
–50
HIGH input level
–
WDI Input Current2
IWDI
LOW input level
–10
HIGH input level
–
INx Input Current2
IINx
LOW input level
–10
Drivers
tp(ON)
INx change to unloaded output change
–
Propagation Delays
tp(OFF)
INx change to unloaded output change
–
IOUTx = 250 mA, VBB = 14 V
–
Driver On-Resistance
RDS(on)
IOUTx = 250 mA, VBB = 9 V
–
IOUTx = 250 mA, VBB = 7 V
–
Driver Leakage Current
IDSS
VOUTx = 40 V
–
Diode Forward Voltage
VF
IOUTx = –250 mA
–
Output Clamp Voltage
VCL
IOUTx = 100 μA
50
Low-Side Driver Overcurrent (O.C.)
IOUT(OC)
275
Threshold
Blanking Time Before Overcurrent Detect
tBLANK
IOUT = 500 mA
2
Regulator
CREG5 ≥ 0.47 μF (X7R Ceramic, ESR ≤ 0. 5Ω),
Voltage Regulator Output Voltage
VREG5
4.9
1 mA ≤ IREG5 ≤ 40 mA
1
Pass Transistor On-Resistance
RREG5
IREG5 = 40 mA
–
Line Regulation Voltage
VLNR
IREG5 = 1 mA
–
1 mA ≤ IREG5 ≤ 40 mA, VBB = 7 V
–
Load Regulation Voltage
VLDR
–
1 mA ≤ IREG5 ≤ 40 mA, VBB ≥ 9 V
VREG5 = 4.63 V, VBB = 7 V
40
Current Limit Level4
IREG5Lim
VREG5 = 4.63 V, VBB ≥ 9 V
65
VREG5 = 0 V
65
VREG5 falling
4.25
Under Voltage Lockout Threshold
VUVREG5
VREG5 rising
4.36
Under Voltage Lockout Hysteresis
VUVREG5hys
–
Typ.
Max.
Units
–
–
–
–
40
4
5
10
V
mA
mA
μA
–
–
–
–
VBB
1.5
5.5
1.5
V
V
V
V
–
–
mV
–
–
–
–
–
–
–
–
–
400
70
10
50
10
50
10
50
10
μA
μA
μA
μA
μA
μA
μA
μA
μA
1
0.5
–
–
–
–
–1.3
–
2
1
5
5.5
6
10
–1.4
60
μs
μs
Ω
Ω
Ω
μA
V
V
–
500
mA
–
20
μs
5.0
5.1
V
–
–
–
–
–
–
–
4.38
4.50
0.12
55
20
100
40
150
200
200
4.63
4.75
–
Ω
mV
mV
mV
mA
mA
mA
V
V
V
Continued on the next page...
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
Relay Driver with 5 V Regulator
for Automotive Applications
A2550
ELECTRICAL CHARACTERISTICS, continued –40°C ≤ TJ ≤ 150°C, VBB within operating limits, unless otherwise noted
Characteristics
Symbol
Test Conditions
Min.
Typ.
Max.
Watchdog and Power-On Reset
NPOR Active Voltage
VNPOR
INPOR = 1 mA; VREG5 = 1.5 V; 1.5 V ≤ VBB ≤ 40 V
–
–
400
–
–
10
NPOR Inactive Leakage Current
INPOR(Off) VNPOR = 5 V
VTRIP(H)
VTRIP(H) = VREF
–
1.2
–
CWD and CPOR Trip Voltage
VTRIP(L)
–
0.2
–
CPOR Charge Current
IPOR
2.5
5
7.5
Power-On Reset Cycle Time5
tPOR
CPOR = 0.22 μF
–
44
–
Charging
2.5
5
7.5
CWD Charge Current
ICWD
Discharging
–
70
–
Thermal Protection
Thermal Shut Down Threshold
TTSD
150
175
–
Thermal Shut Down Hysteresis
TTSDhys
–
15
–
Units
mV
μA
V
V
μA
ms
μA
μA
°C
°C
1See Applications
Information section for operation with VBB < 7 V. For VBB > 24 V, thermal constraints limit regulator current.
input and output current specifications, negative current is defined as coming out of (sourcing) the specified device pin.
3When V
ENBAT exceeds VBB it is clamped with a diode. (VENBAT – VBB) ≤ 1.2 V at 40 mA.
4Defined as the maximum current level allowed during excessive load condition.
5See Applications Information section for calculations. Values guaranteed by design, and depend on capacitor tolerances.
2For
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic
Symbol
Thermal Resistance, Junction to Pad
RθJP
Thermal Resistance, Junction to
Ambient
RθJA
Maximum Allowable Power Dissipation
PD
Test Conditions*
4-layer PCB based on JEDEC standard
2-layer PCB with 2 in.2 copper both sides
RθJA = 44 ºC/W (estimated), 2-layer PCB with 2.0
TA = 125°C
in.2
of 2 oz. copper,
RθJA = 44 ºC/W (estimated), 2-layer PCB with 2.0 in.2 of 2 oz. copper,
TA = 85°C
Value
Units
2
ºC/W
34
ºC/W
44
ºC/W
0.57
W
1.48
W
*Additional thermal data available on the Allegro Web site.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
Relay Driver with 5 V Regulator
for Automotive Applications
A2550
Dynamic Thermal Impedance
Square Wave Power Pulse in a Single Output Stage
20
18
Impeda nce (°C/W)
16
14
12
10
8
6
4
2
0
0.01
0.1
1
10
100
Time (ms)
Figure 1. Dynamic thermal impedance of an individual output stage during active clamp
of an inductive load (mounted on a 4-layer PCB based on JEDEC standard).
Nonrepetitive Output Active Clamp Power Dissipation
POUT (W)
100
10
TJ = 25°C
TJ = 125°C
1
0.01
0.1
1
10
100
Time (ms)
Figure 2. Peak power dissipation curves for nonrepetitive clamped outputs. Output
voltage is clamped during turn-off of inductive loads while current decays.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
Relay Driver with 5 V Regulator
for Automotive Applications
A2550
Functional Description
Pin Descriptions
EN Enable pin; logical OR with ENBAT. This logic-level
input enables the A2550. If there are no faults, the regulator
is live and outputs can be switched. When both the EN and
ENBAT pins are held low, the A2550 enters Sleep mode.
ENBAT Enable pin; logical OR with EN. Same as EN,
except that this pin is high-voltage protected, and specified
up to VBB so it can be tied to the battery or power source.
Not to exceed VBB because the ESD structure places a diode
between the ENBAT and VBB pins.
WDI Watchdog Input. Monitors the microcontroller to detect
when it stops functioning. This pin is connected to an edge
trigger. To avoid a fault, the latter must be triggered before
CWD times-out. When not used, WDI is defeated by tying it
to NPOR and shorting CWD.
CWD Watchdog timer capacitor terminal. Used with WDI.
A current source charges the external capacitor tied to this
pin. A reverse current source discharges the capacitor when
either WDI transitions or the high Trip Voltage, VTRIP(H) , is
reached (see specification table for values). The charge-up
time defines the maximum period allowed WDI to toggle
before a fault is issued; the charge-down time defines the
width of NPOR pulses issued to wake-up the microcontroller.
NPOR NOT Power On Reset. This active-low pin indicates
a fault. Except for watchdog faults, NPOR is held low during
the fault state. Refer to the Fault Logic table to determine
which faults are latched. Watchdog faults generate a train of
pulses to “wake up” the microcontroller.
CPOR Power-On Reset timer capacitor terminal. Whenever VREG5 first charges up (at start-up or when a fault
is cleared) a “fault” condition remains in effect until the
onboard current source drives CPOR to the high Trip Voltage, VTRIP(H) . This allows external circuits, such as a microcontroller, to be initialized before activating the outputs.
CPOR is defeated by pulling it high to VREG5 with a 50 k
resistor.
INx Input pin. Active-high CMOS input. Internally tied to
200 k pull-down resistors.
OUTx Output pin. Open drain DMOS. Clamps to a voltage
greater than VBB when an inductive load is switched off.
Includes current mirror for overcurrent protection.
VBB Power pin, or “battery.” Specified for automotive voltages.
VREG5 5 V Regulator output. Clamped at the Current
Limit Level (IREG5Lim) for excessive loads. As load resistance
decreases, VREG5 is pulled below the UVLO level. In that
case, a fault is generated (NPOR low).
LGND Logic Ground. The reference pin for the logic
circuits. Must be connected to PGND externally.
PGND Power Ground. The reference pin for the outputs
(OUTx). Must be connected to LGND externally.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7
Relay Driver with 5 V Regulator
for Automotive Applications
A2550
Timing Diagram: Initial Start-up and Exiting Sleep Mode
VBB
VREG5
WDI
Internal Vref
CWD
EN or
ENBAT
tPOR
tPOR
Internal Vref
CPOR
NPOR
OUTx
1
1.
2.
3.
4.
~INx
~INx
2
3
4
5 V signal to wake up microcontroller.
OUTx enabled with first watchdog pulse.
Power ramp-up sequence with watchdog active.
NPOR inactive, but outputs not enabled until watchdog detected.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
8
Relay Driver with 5 V Regulator
for Automotive Applications
A2550
Timing Diagram: Watchdog Monitoring
5
W
i ter al ref
CW
tW
tW
C
N
U
out uts e a le
N
1
1.
2.
3.
4.
3
Missing watchdog detected (WDI low).
NPOR pulses generated periodically.
NPOR inactive, but outputs not enabled until watchdog detected.
Missing watchdog detected (WDI low, steps 2 and 3 repeat).
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
9
Relay Driver with 5 V Regulator
for Automotive Applications
A2550
Timing Diagram: VREG5 UVLO and TSD Monitoring
VBB
VUVREG5
VREG5
WDI
Internal Vref
CWD
Internal
VREG5 UVLO
Internal Vref
CPOR
NPOR
Internal
TSD
OUTx
outputs enabled
1
1.
2.
3.
4.
5.
~INx
~INx
2
3
4
5
VREG5 undervoltage detected.
VREG5 recovers, and after it rises above VUVREG5 + VUVREG5(Hys),
UVLO flag is deactivated and CPOR recharges.
NPOR inactive, but outputs not enabled until watchdog detected.
TSD event detected and NPOR is activated. When VREG5 ≤ VUVREG5 ,
VREG5 shuts down.
TSD flag deactivated (VREG5 allowed to rise; steps 2 and 3 repeat)
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
10
Relay Driver with 5 V Regulator
for Automotive Applications
A2550
Applications Information
Dropout Voltage
NPOR
For operation with VBB below the specified range of operating 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:
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)
IREG5 <
VBB − VREG5
R REG5
(1)
Figure 3 shows the results of this condition combined with
the rated regulator current, in normal operation.
70
60
IREG5(max) (mA)
Note that, although the regulator is specified for normal
operation with VBB well above normal automotive voltages,
in general thermal constraints will limit maximum operational VBB.
Fault Logic
50
40
30
20
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.
10
0
0
5
10
15
20
VBB (V)
Figure 3. Current Capability of the 5 V Regulator (VREG5)
Table 1. Fault Logica
TSD
UVLO
Watchdog
alarm
OCx
Internal 5V
VREG5
NPOR
OUTx
Outputs
EN OR
ENBATb
Inputs
1
0
0
0
0
1
1
1
INx
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
Z
aX
Mode of Operation
Normal Operation: OUTx active for INx active.
Sleep mode. NPOR = 0 when pulled up by VREG5
because VREG5 = 0.
indicates “don’t care,” Z indicates high impedence.
entry is a logical OR of the EN and ENBAT pins.
bThis
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115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
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11
Relay Driver with 5 V Regulator
for Automotive Applications
A2550
Applications Information
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 tPOR period. The latter is set by the value of the external
capacitor fed by a current source at the CPOR pin, according
to the following formula:
t POR = ⎛200 ms ⎞ CPOR
µF ⎠
⎝
(2)
The scaling factor is simply derived from the specifications
using the typical value of IPOR:
t POR
CPOR
=
VREF − VTRIP(L)
I POR
(3)
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, tWD , the watchdog activates
NPOR, which pulses periodically. tWD is proportional to
the external capacitor fed by a current source at the CWD
pin. The voltage change is 1 V, so using the typical value of
ICWD(charging) we have:
tWD = ⎛200 ms ⎞ CWD
µF ⎠
⎝
(4)
The pulse width for NPOR active, tWDR, also scales proportionally to the value of the external capacitor at the CWD
pin. Using the typical value of ICWD(discharging) we have:
tWDR = ⎛14 ms ⎞ CWD
⎝ µF ⎠
(5)
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.
Table 2. Timing Set by Capacitors
C
(μF)
tPOR
(ms)
tWD
(ms)
tWDR
(ms)
0.1
20
20
1
0.22
44
44
3
0.47
94
94
7
1
200
200
14
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 normally. 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 overcurrent 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, disable sleep mode by tying ENBAT to VBB.
Power Limits
Power dissipation, PD , is limited by thermal constraints. The
maximum allowed power dissipation, PD(max) , is found from
the formula:
TJ = (PD(max) R θJA+ TA ) ≤ TJ(max)
(6)
The maximum junction temperature, TJ(max) , and the thermal
resistance, RθJA , are given in the specification tables.
The three main contributors to power dissipation are:
• PBIAS from the supply bias current
• PREG from the linear regulator voltage drop
• PLS from low-side driver conduction
For example, to determine if TJ is in an acceptable range,
given:
RθJA = 55°C/W , and
TA = 125°C ; and
PBIAS = VBB × IBBQ
(7)
= 14 V × 3 mA = 42 mW , and
PREG = (VBB – VREG5(min)) × IREG5
(8)
= (14 V – 4.9 V) × 20 mA= 182 mW , and
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115 Northeast Cutoff
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12
Relay Driver with 5 V Regulator
for Automotive Applications
A2550
PLS = (RDS(on) × I2LS1) + (RDS(on) × I2LS2)
(9)
The output voltage is clamped to protect the driver. The
active clamp works as follows. The voltage at the driver output is pushed high by the inductive current. Once the clamp
voltage, VCL , is reached, a Zener diode conducts current to
the internal FET gate driver block. Therefore, the FET turns
partially on, in order to limit any further increase in voltage
at the output pin. The output is then held at this clamp voltage until the current decays to zero, as shown in figure 4.
(10)
Energy loss in the chip, E, may be calculated as follows.
Load coil resistance, RCOIL , is usually a significant value,
but a worst case scenario takes RCOIL = 0 for simplicity. With
active clamping at VCL , the output current (with initial value
IOUT0) is driven low and the upper limit on energy loss in the
driver is calculated as:
+ (RDS(on) × I2LS3) .
Because ILS1 = ILS2 = ILS3 = 110 mA , and
given that RDS(on) = 5 Ω, then
PLS = 3 (5 Ω) * (110 mA) 2 = 182 mW .
Given also:
PD = PBIAS + PREG + PLS
= 42 mW+ 182 mW+ 182 mW = 406 mW .
TJ can be calculated by substitution into equation 6:
TJ = 0.406 W × 55°C/W +125°C = 147°C .
Reverse Battery
The low-side driver outputs can withstand reverse battery
when the load (RLOADx) is connected to limit current. Power
dissipation (PD = PLS(rvrs)) is limited by thermal constraints,
according to the following formula:
PLS(rvrs) = VF1× IF1+ VF2× IF2+ VF3× IF3 ,
(11)
Emax = 1 IOUT0 VCL Δ t .
2
(14)
LCOIL IOUT0 ,
VCL – Vdc
(15)
From figure 4:
Δt =
and
–1
2
Emax = 1 L COIL IOUT0 (1– Vdc / VCL ) .
2
where:
IFx =
VBB(rvrs) −VFx .
RLOADx
(12)
Active Clamp on Outputs
IOUT
The driver section includes an active clamp that prevents an
overvoltage when an inductive load is switched off. Zener
diodes are connected at the output pins. This removes the
need for external freewheeling diodes across inductive loads.
The coil current, ICOIL , is quenched by allowing the output
pin voltage, VOUTx , to exceed the battery voltage at the load,
Vdc. This applies a negative voltage drop across the load.
Therefore the current gradient is driven negative, as shown in
the following formula:
dICOIL
dt
=
Vdc − VOUT − ICOIL×RCOIL
L COIL
(16)
<0 .
(13)
IOUT0 =
Vdc
RCOIL
m=
–(VCL – Vdc)
LCOIL
Δt
Figure 4. Output Voltage Clamping
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
13
Relay Driver with 5 V Regulator
for Automotive Applications
A2550
A more rigorous derivation, including RCOIL during the
Capacitive Loads
exponential current decay results in:
When capacitive loads are applied to the outputs, the
constraint described below applies. Such is the case, for
example, when capacitors are attached to the outputs to
protect against ESD. Larger capacitors protect against larger
ESD voltages. However, the upper limit on capacitance is
determined by the blanking time. The latter allows for spurious current spikes and capacitor discharges to be completed
before the overcurrent detection circuit senses the output current (see tBLANK in the Electrical Characteristics table). The
blanking time allows a 47 nF capacitor with 20% tolerance
and nominal 12 V automotive voltages.
and
V
V
R
i ( t ) = R dc − R CL ⎡⎢⎢1− exp ⎛− t LCOIL
⎝
COIL
COIL ⎣
COIL
Δt =
⎞ ⎥⎤ ,
⎠ ⎥⎦
LCOIL
−1
ln (1 – Vdc VCL ) .
RCOIL
(17)
(18)
Energy loss in the driver is:
E=
VCL VDC LCOIL
2
RCOIL
[1+ (VCL Vdc −1 ) ln (1 − Vdc VCL)] . (19)
Pin-out Diagram
IN1 1
16 OUT1
IN2 2
15 OUT2
IN3 3
14 OUT3
LGND 4
NPOR 5
13 PGND
12 CWD
WDI 6
11 CPOR
EN 7
10 ENBAT
VREG5 8
Terminal List Table
No.
Name
1
IN1
2
IN2
3
IN3
4
LGND
5
NPOR
6
WDI
7
EN
8
VREG5
9
VBB
10
ENBAT
11
CPOR
12
CWD
13
PGND
14
OUT3
15
OUT2
16
OUT1
–
PAD
PAD
9 VBB
Description
Activate driver 1
Activate driver 2
Activate driver 3
Logic ground; must be connected to PGND externally
Not Power-On Reset
WatchDog Input
Enable (low voltage)
5V regulator
Supply voltage
Enable (high voltage)
Capacitor terminal for Power-On Reset cycle time
Capacitor terminal for WatchDog timing
Power ground; must be connected to LGND externally
Low side driver 3
Low side driver 2
Low side driver 1
Exposed pad for enhanced thermal performance
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
14
Relay Driver with 5 V Regulator
for Automotive Applications
A2550
16-Pin TSSOP (Suffix LP) with Exposed Pad
0.45
5.00 ±0.10
16
+0.05
0.15 –0.06
0.65
16
4° ±4
1.70
B
4.40 ±0.10
3.00
6.40 ±0.20
0.60 ±0.15
A
1
(1.00)
2
3.00
16X
0.25
SEATING
PLANE
0.10 C
+0.05
0.25 –0.06
3.00
0.65
1.20 MAX
0.15 MAX
C
SEATING PLANE
GAUGE PLANE
1 2
3.00
C
PCB Layout Reference View
For Reference Only
(reference JEDEC MO-153 ABT)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
A Terminal #1 mark area
B Exposed thermal pad (bottom surface)
C Reference land pattern layout (reference IPC7351 SOP65P640X110-17M);
All pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary
to meet application process requirements and PCB layout tolerances; when
mounting on a multilayer PCB, thermal vias at the exposed thermal pad land
can improve thermal dissipation (reference EIA/JEDEC Standard JESD51-5)
Copyright ©2006-2013, Allegro MicroSystems, LLC
Allegro MicroSystems, LLC 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, LLC assumes no responsibility for its
use; nor for any infringement of patents or other rights of third parties which may result from its use.
For the latest version of this document, visit our website:
www.allegromicro.com
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
15
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