ALM2403-Q1
ZHCSMT3A –NOVEMBER 2020 –REVISED MARCH 2023
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8.2.2 Detailed Design Procedure
When using the ALM2403-Q1 in a resolver application, determine:
• Resolver excitation input impedance or resistance and inductance: ZO = 100 + j188, R = 100 Ω, and
L = 3 mH at 10 kHz
• Resolver transformation ratio (VSINCOS / VEXC): 0.5 V/V at 10 kHz
• Package and RθJA: HTSSOP, 46.9°C/W
• Op amp maximum junction temperature: 150°C
• Op amp bandwidth: 21 MHz
• Op amp slew rate: 50 V/µS
8.2.2.1 Resolver Excitation Amplifier Combined With MFB 2nd-Order, Low-Pass Filter
R2
6 kΩ
C1
159 nF
C3 1 nF
R1
2 kΩ
R3
2 kΩ
œ
VOUT1
PWM input
C2
12 nF
VBIAS
+
ALM2403-Q1
SD1 1N5827
15 V
图8-3. Two-Pole MFB Filter
When designing a low-pass filter, the most important design criteria is to decide the corner frequency. In this
design example, the resolver excitation frequency is 10 kHz and PWM frequency is 320 kHz. Thus, we want to
make sure that the low-pass filter corner frequency is greater than 10 kHz, and there is maximum attenuation of
harmonic interference generated from the PWM signal. 图 8-3 shows a single channel of the ALM2403-Q1
configured as a 2-pole multiple feedback (MFB) filter with a –40 dB/decade rolloff. The MFB topology enables a
steep rolloff while reducing BOM count. The output from this circuit is a sine wave that can then be inverted
using the second channel of the ALM2403-Q1; see 图 8-2. Thus, both ALM2403-Q1 channels combined provide
the required resolver excitation signal.
8.2.2.1.1 Filter Design
The corner frequency of the 2nd-order MFB filter is set to approximately twenty times less than the PWM
frequency. The corner frequency defined at –3 dB is shown in 方程式1.
1
f
=
(1)
p
2 × π ×
R × C × R × C
3 3 2 2
The 2nd-order MFB active filter uses an inverted input topology and the op amp gain is determined by the ratios
of resistors R2 and R1:
R
2
Gain = −
(2)
R
1
The gain settings are based on the output drive requirements and PWM signal amplitude. With different gain
settings, the filter characteristics, such as rolloff, can change. The design must be fine-tuned to meet optimal
performance needs.
The quality (Q) factor of the low-pass filter is configured with Q = 1. The purpose of designing for this Q factor is
to minimize attenuation around the corner frequency of 10 kHz, thus extending the pass-band gain. The Q factor
of the 2nd-order MFB filter is given by 方程式3:
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Product Folder Links: ALM2403-Q1
English Data Sheet: SBOSA37
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