DRV590_16 Datasheet, PDF (9/18 Pages) Texas Instruments – 1.2-A HIGH-EFFICIENCY PWM POWER DRIVER

DRV590
SLOS365A – AUGUST 2001 – REVISED AUGUST 2002
APPLICATION INFORMATION
driving TEC elements (continued)
filter component selection
The LC filter may be designed from a couple of different perspectives, both of which may help estimate the
overall performance of the system. The filter should be designed for the worst-case conditions during operation,
which is typically when the differential output is at 50% duty cycle. The following section serves as a starting
point for the design, and any calculations should be confirmed with a prototype circuit.
To simplify the design, half-circuit analysis may also be used. This should only be done if the TEC element is
close to the output of the filter. Any filter should always be placed as close to the DRV590 as possible to reduce
EMI.
OUT+
OUT–
L
C
C
L
C
TEC R
OUT+
or
OUT–
L
2C
C
TEC R
2
Figure 10. LC Output Filter
Figure 11. LC Half-Circuit Equivalent
LC filter in the frequency domain
The transfer function for the second order low-pass filter in Figure 10 and Figure 11 is shown in equation 2.
ǒ Ǔ ^{HLP(jw) +}
1
2
–
w
w₀
)
1
Q
jw
w₀
)
1
(2)
w₀ + _ǸL
1
3C
Q = quality factor
ω = DRV590 differential switching frequency
For the DRV590, the differential output switching frequency is 500 kHz. The resonant frequency for the filter
should be chosen to be at least one order of magnitude lower than the switching frequency. Equation 2 may
then be simplified to give the following magnitude equation 3. These equations assume the use of the filter in
Figure 10, which effectively triples the capacitance.
ǒ Ǔ ^ŤHLP^Ť_dB + –40 log
fs
fo
(3)
fo
+
2p
1
Ǹ_L
3C
f_s = 500 kHz (DRV590 differential switching frequency)
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