ALM2403-Q1
ZHCSMT3A –NOVEMBER 2020 –REVISED MARCH 2023
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C
/C
3
2
Q =
(3)
R
/R
+
R
/R
+
R × R /R
3 2 1
3
2
2
3
8.2.2.1.2 Short-to-Battery Protection
Resolver-based applications require the power op amp stage to provide the resolver excitation signal over long
cables. In many applications, such as automotive traction inverters, the cables are housed in a harness and a
short-circuit condition between different cables in the same harness can occur. In this situation, the output of the
ALM2403-Q1 can see a higher voltage than provided at the positive supply pin. This condition causes the body
diode in the output stage PMOS to become forward-biased and start conducting. As a precaution, use a blocking
diode in series with the positive power supply; see also 图8-3.
For related information, see the ALM2403-Q1 Overvoltage Protection of Resolver-Based Circuits application
note.
8.2.2.2 Power Dissipation and Thermal Reliability
Power dissipation is critical to many industrial and automotive applications. Resolvers are typically chosen over
other position feedback techniques because of reliability and accuracy in harsh conditions and high
temperatures.
The ALM2403-Q1 is capable of high output current with power-supply voltages up to 24 V. Internal power
dissipation increases when operating at high supply voltages. The power dissipated in the op amp (POPA) is
calculated using 方程式4:
V
OUT
P
=
V − V
× I
=
V − V ×
OUT
(4)
OPA
S
OUT
OUT
S
R
L
To calculate the worst-case power dissipation in the op amp, the ac and dc cases must be considered
separately.
In the case of constant output current (dc) to a resistive load, the maximum power dissipation in the op amp
occurs when the output voltage is half the positive supply voltage. This calculation assumes that the op amp is
sourcing current from the positive supply to a grounded load. If the op amp sinks current from a grounded load,
modify 方程式5 to include the negative supply voltage instead of the positive.
2
V
V
S
S
P
= P
=
(5)
OPA MAX⎽DC
OPA
2
4 × R
L
The ac maximum of average power dissipation in the op amp for a sinusoidal output current (ac) to a resistive
load occurs when the peak output voltage is 2/π times the supply voltage, given symmetrical supply voltages,
as shown in 方程式6:
2
2 × V
OPA
π
2 × V
S
S
P
= P
=
(6)
OPA PEAK⎽AC
2
π
× R
L
After the total power dissipation is determined, the junction temperature at the worst expected ambient
temperature case must be determined by using 方程式7:
T
= P
× R
+ T
A MAX
(7)
J MAX
OPA
θJA
8.2.2.2.1 Improving Package Thermal Performance
The value of RθJA depends on the printed circuit board (PCB) layout. An external heat sink, a cooling
mechanism such as a cold air fan, or both, can help reduce RθJA, and thus improve device thermal capabilities.
See TI’s design support web page at www.ti.com/thermal for general guidance on improving device thermal
performance.
Copyright © 2023 Texas Instruments Incorporated
English Data Sheet: SBOSA37
18
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