Datasheet

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SLOS389A – NOVEMBER 2001– REVISED MAY 2002
www.ti.com
11
APPLICATION INFORMATION
1 µF
AVDD
AGND (Connect to PowerPAD)
ROSC
COSC
AREF
IN+
IN–IN–
FAULT1 FAULT0 PVDD PVDD PVDD OUT– OUT– OUT–
OUT–
PGND
PGND
PGND
PGND
PGND
PGND
OUT+
OUT+ OUT+ OUT+
PVDD PVDD PVDD FREQ
120 kΩ
220 pF
1 µF
Shutdown Control
1 kΩ
1 kΩ
DC Control
Voltage
10 µF
VDD
10 µH
10 µF
10 µH
10 µF
1 µF
FAULT1
FAULT0
To TEC or Laser
Diode Anode
To TEC or Laser
Diode Cathode
1 µF
SHUTDOWN
INT/EXT
Figure 16. Typical Application Circuit
OUTPUT FILTER CONSIDERATIONS
TEC element manufacturers provide electrical
specifications for maximum dc current and maximum
output voltage for each particular element. The maximum
ripple current, however, is typically only recommended to
be less than 10% with no reference to the frequency
components of the current. The maximum temperature
differential across the element, which decreases as ripple
current increases, may be calculated with the following
equation:
DT +
1
ǒ
1 ) N
2
Ǔ
DT
max
Where:
∆T = actual temperature differential
∆T
max
= maximum temperature differential
(specified by manufacturer)
N = ratio of ripple current to dc current
According to this relationship, a 10% ripple current
reduces the maximum temperature differential by 1%. An
LC network may be used to filter the current flowing to the
TEC to reduce the amount of ripple and, more importantly,
protect the rest of the system from any electromagnetic
interference (EMI).
FILTER COMPONENT SELECTION
The LC filter, which may be designed from two different
perspectives, both described below, helps 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 in the lab.
Any filter should always be placed as close as possible to
the DRV591 to reduce EMI.
Figure 17. LC Output Filter
C
TEC
C
OUT+
OUT–
R
L
L
Figure 18. LC Half-Circuit Equivalent
(for DRV591 Only)
C
TEC
OUT+
or
OUT–
R
L
(1)