Tripath Technology, Inc. - Technical Information
will not saturate during short circuit events; this is why they are not recommended for use with the
TA2022. Also it should be noted that shielded bobbin construction is not as effective as toroidal
construction for EMI containment.
Tripath recommends that the customer use a toroidal inductor with a Carbonyl-E core for all
applications of the TA2022. This core has a high peak current capability due to its low-µ Carbonyl-E
metal powder. A distributed air gap increases its’ energy storage capability, which allows for a small
footprint and high current capability. Carbonyl-E toroidal iron powder cores have low loss and good
linearity. The toroidal shape is ideal for EMI containment. Also, EMI can be further contained by sizing
the toroid to accept a full layer of windings. This aids in shielding the electric field. Tripath
recommends:
-
Micrometals (www.micrometals.com) Type-2 (Carbonyl-E) toroidal iron powder cores. The
specific core Tripath initially verified and used on the EB-TA2022 was a T94-2 (23.9mm
outer diameter) wound to 11uH with 19AWG wire. Since then Tripath has determined that
much smaller Carbonyl-E toroids will not saturate during high current events. Tripath has
also used T68-2 (17.5mm outer diameter) and the T60-2B/60(15.2mm outer diameter)
cores wound to 11uH with 22AWG with good success. If a smaller core is required, core
outer diameters as small as 15.2mm (T60-2) work well, but core temperature effects should
be tested. The T60-2 core did not saturate during short circuit testing, but maximum core
temperatures must be considered and multiple layer winding must be used to achieve
11uH. Multiple winding can increase winding capacitance, which may cause ringing and
increased radiated emissions. Bank winding techniques can minimize this effect. It should
be noted that at core temperatures above 130C the single build wire used by most inductor
manufacturers should be replaced with a heavy build wire. Micrometals does not provide
winding services, but many companies purchase directly from them and provide completely
finished inductors. Pulse Engineering has assigned a part number for the T68-2 wound with
44 turns of 22 AWG single build wire. The part number is PA0291.
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Amidon Inc./American Cores type-06 (Carbonyl-E) toroidal iron powder cores. Tripath has
used T690-06 (17.5mm outer diameter) cores wound to 11uH with good success. Amidon
carries type-06 cores in the 23.9mm to 15.2mm outer diameter range. They have assigned
a part number for the T690-06 wound with 44 turns of 22 AWG single build wire. This part
is approved by Tripath and is 690064422.
Power Supplies
The TA2022 requires the split supply rails VPP1(VPP2) and VNN1(VNN2), and V5. It also uses
some additional voltages, VN10, VBOOT1 and VBOOT2 that are generated internally. The selection
of components for the switching regulator is shown in the Application / Test Diagram.
Minimum and Maximum Supply Voltage Operating Range
The TA2022 can operate over a wide range of power supply voltages from +/-12V to +/-36V. In order
to optimize operation for either the low or high range, the user must select the proper values for
R
VNNSENSE, RVPPSENSE, RFBA, RFBB, and RFBC. Please refer to the Modulator Feedback Design and
Over/Under-voltage Protection sections for more additional information.
VN10 Supply
The TA2022 has an internal hysteretic buck converter, which, in conjunction with a few passive
components, generates the necessary floating power supply for the MOSFET driver stage (nominally
11V with the external components shown in Application / Test Circuit). The performance curves
shown in the data sheet as well as efficiency measurements were done using the internal VN10
generator. Tripath recommends that the internal VN10 generator be used.
In some cases, though, a designer may wish to use an external VN10 generator. The specification
for VN10 quiescent current (65mA typical, 80mA maximum) in the Electrical Characteristics section
states the amount of current needed when an external floating supply is used. If the internal VN10
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TA2022 – KLI/1.2/07-04
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
