A3944KLPTR-T Allegro Microsystems Inc, A3944KLPTR-T Datasheet - Page 27

• Manufacturer Part Number: A3944KLPTR-T
• Description: IC PREDRIVER MOSFET 6CH TSSOP
• Manufacturer: Allegro Microsystems Inc

Specifications of A3944KLPTR-T

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

A3944
The variation of R
line (Maximum Short Resistance) in figure 18. This example
shows the maximum possible resistance of a short to battery
that will always be detected as a short with a 2.8 Ω load and a
100 mΩ MOSFET using short to battery threshold level 5.
As R
The expression for R
Figure 18. Short to battery detection limits
L
increases, R
R
SB
V
V
<
D
D
SBmax
=
=
SB
(V
R
SB
L
R
becomes the dominant resistance and:
V
SB
R
L
– V
L
(from equation 15) becomes:
L
with load voltage is shown as the lower
+ R
R
+ R
V
V
R
STB
SB
STB
L
ON
SB
ON
R
)R
ON
+ R
ON
ON
Automotive, Low Side FET Pre-Driver
(18)
(19)
This allows a lower threshold to be used for V
faster short to battery detection and a lower short circuit current.
Minimum load resistance
For normal operation:
and:
Rearranging gives:
The minimum value of the load resistance, R
a short to battery detection under normal operating conditions is
given by:
The variation of R
line (Minimum Load Resistance) in figure 18. This example
shows the minimum possible load resistance that will always
allow a short to battery to be detected with a 0.5 Ω short and a
100 mΩ MOSFET using short to battery threshold level 5.
Power Dissipation Estimation
The A3944 supply currents have very little dependency on the
state of the internal circuits. In addition, the internal operation
is essentially low speed so the power dissipation has almost no
dependency on operating frequency other than dissipation due
to channel switching and diagnostics that are proportional to
PWM frequency. It is therefore possible to estimate the maximum
power dissipated within the A3944 by summing the contribution
from the three quiescent supply currents with the dissipation due
to channel switching and diagnostics associated with turning each
external MOSFET on and off.
R
Lmin
=
R
Lmin
V
L
(V
DRNx
>
Lmax
V
(V
with load voltage is shown as the upper
DRNx
=
L
– V
– V
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
R
V
V
V
< V
L
STBmin
STB
STBmin
L
STB
+ R
R
STB
ON
)R
ON
ON
)R
ONmax
L
, that will not cause
STB
, resulting in a
(20)
(21)
(22)
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