A2550KLP-T Allegro Microsystems Inc, A2550KLP-T Datasheet - Page 13

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

Specifications of A2550KLP-T

• Lead Free Status / RoHS Status: Compliant

A2550
Because I
given that R
Given also:
T
Reverse Battery
The low-side driver outputs can withstand reverse battery
when the load (R
dissipation (P
according to the following formula:
where:
Active Clamp on Outputs
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, I
pin voltage, V
V
Therefore the current gradient is driven negative, as shown in
the following formula:
J
dc
can be calculated by substitution into equation 6:
. This applies a negative voltage drop across the load.
P
P
P
T
LS
LS
D
J
dI
= (R
= 3 (5 Ω) * (110 mA)
= P
= 42 mW+ 182 mW+ 182 mW = 406 mW .
= 0.406 W × 55°C/W +125°C = 147°C .
LS1
dt
+ (R
COIL
P
DS(on)
BIAS
DS(on)
LS(rvrs)
= I
D
OUTx
DS(on)
= P
LS2
+ P
LOADx
COIL
= 5 Ω, then
V
× I
I
, to exceed the battery voltage at the load,
LS(rvrs)
=
Fx
REG
dc
× I
= I
V
2
LS1
F1
, is quenched by allowing the output
2
) is connected to limit current. Power
LS3
LS3
+ P
×
V
V
) + (R
) is limited by thermal constraints,
I
BB(rvrs)
OUT
F1
) .
= 110 mA , and
LS
R
L
+
LOADx
COIL
V
2
DS(on)
F2
= 182 mW .
I
×
COIL
V
I
F2
Fx
× I
+
×
V ×
2
.
R
LS2
F3
COIL
)
I
F3
,
0
.
(10)
(11)
(12)
(13)
(9)
The output voltage is clamped to protect the driver. The
active clamp works as follows. The voltage at the driver out-
put is pushed high by the inductive current. Once the clamp
voltage, V
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 volt-
age until the current decays to zero, as shown in figure 4.
Energy loss in the chip, E, may be calculated as follows.
Load coil resistance, R
but a worst case scenario takes R
active clamping at V
I
driver is calculated as:
From figure 4:
and
OUT0
Relay Driver with 5 V Regulator
I
OUT
) is driven low and the upper limit on energy loss in the
Figure 4. Output Voltage Clamping
for Automotive Applications
CL
E
, is reached, a Zener diode conducts current to
max
E
max
t
1
2
CL
L
L
V
COIL
, the output current (with initial value
COIL OUT0
COIL
CL
1
2
–
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
, is usually a significant value,
I
I
V
I
OUT0
OUT0
dc
2
I
COIL
V
(1–
OUT0
CL
,
V
=
= 0 for simplicity. With
dc
t
R
.
/
V
Δt
COIL
V
dc
CL
m =
)
–1
–(V
.
CL
L
COIL
– V
dc
(14)
(15)
(16)
)
13