A3944KLPTR-T Allegro Microsystems Inc, A3944KLPTR-T Datasheet - Page 22

• 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 maximum repetition rate of this pulse is derived from the
maximum average clamp power dissipation limit. The minimum
time between pulses, t
where P
Substituting into equation 3:
resulting in a repetition rate of just over 20 kHz.
Maximum energy example:
• Load resistance: 18 Ω
• Load inductance: 1 mH
• Load current: 0.72 A
• Load supply voltage: 13 V
• FET clamp voltage: 80 V
These values would typically apply to a small inductive load
such as a solenoid or relay. When the load is switched off, the
inductance attempts to keep the current flowing by increasing
the voltage at the end connected to the FET switch. This voltage
increases up to the breakdown voltage of the FET. At that point,
the voltage across the load amounts to the difference between
the FET breakdown voltage and the supply voltage, and it acts to
reduce the current. With the parameters in this example, the cur-
rent would decay to zero in about 10 μs. This is greater than the
1.85 μs pulse time defining the maximum current but less than
the 2 ms time constant for maximum average clamp power, so
the drain resistor will be selected to limit the energy injected into
the drain clamp in the A3944. The maximum current, the A3944
drain clamp maximum current, I
where
E
V
t
PULSE
DRNC
DCL
is the A3944 drain clamp voltage, and
DRNC
is the duration of the current pulse.
is the A3944 drain clamp maximum energy,
is the A3944 drain clamp maximum power.
t
I
t
REP
DRNC
REP
REP
=
=
=
100 mW
, is:
E
P
4.86 μJ
V
DRNC
DRNC
DCL
E
DRNC
DRNC
× t
= 48.6 μs
PULSE
, will be:
Automotive, Low Side FET Pre-Driver
(3)
(4)
Substituting into equation 4:
As given in equation 1, the value of the drain resistor is the volt-
age across the resistor divided by the maximum current:
As given in equation 3, the maximum repetition rate of this pulse
is derived from the maximum average clamp power dissipation
limit as:
resulting in a repetition rate of 10 kHz.
Maximum power example:
• Load resistance: 5 Ω
• Load inductance: 80 mH
• Load current: 2.6 A
• Load supply voltage: 13 V
• FET clamp voltage: 60 V
These values would typically apply to a large inductive load
such as a coil or actuator. When the load is switched off, the
inductance attempts to keep the current flowing by increasing
the voltage at the end connected to the FET switch. This voltage
increases up to the breakdown voltage of the FET. At that point,
the voltage across the load amounts to the difference between
the FET breakdown voltage and the supply voltage, and it acts
to reduce the current. With the parameters in this example, the
current would decay to zero in about 4 ms. This is greater than
the 2 ms time constant for maximum average clamp power, so
the drain resistor will be selected to limit the power dissipated by
I
DRNC
R
R
t
t
REP
REP
Dx
Dx
=
=
=
=
=
54 V × 10 μs
V
80 V – 54 V
100 mW
FET
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
18.5 mA
E
P
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
10 μJ
I
10 μJ
DRNC
DRNC
DRNC
– V
DCL
= 100 μs
= 18.5 mA
= 1.4 kΩ
:
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