Tripath Technology, Inc. - Technical Information
1/2 TA2022
V5
RFBA
RFBA
RFBC
RFBC
Processing
&
FBKOUT1
FBKGND1
OUT1
OUT 1 GROUND
Modulation
ROFB
10K
RFBB
RFBB
ROFA
50K
AGND
Figure 5: Manual Output Offset Trim Circuit
A DC servo can also be used to automatically null any offset voltage. The TA2022 evaluation board
incorporates a DC servo. Please refer to the TA2022 evaluation board document, EB-TA2022,
available on the Tripath website, at www.tripath.com.
Current Protection Design
Although the over-current (Ioc) trip point is internally fixed, there are external components that can
affect output current levels during a short circuit event. Referring to the Application/Test diagram
these include the output inductor (Lo), output diodes (Do) and supply bypassing (Cs).
The two output inductors, Lo, directly impact the peak output current levels reached during short
circuit events. For this reason they must be rated at least 10A regardless of the systems maximum
operating current, ensuring the inductor does not saturate which could lead to switching currents
passing unimpeded to the load. When this occurs, the Ioc may be forced to trip on average current
levels instead of peak current levels, directly impacting the current levels seen by the load and
potentially causing damage to the TA2022. Please refer to the Output Filter Design section for more
details on the inductor requirements and figure 6 for comparison of load currents with an unsaturated
and saturated inductor.
The four output diodes, Do, minimize overshoots and undershoots with respect to the supply rails
VPP and VNN. In order for these diodes to work properly they must have a low Forward Voltage
rating at 10A. We recommend a Fast Recovery diode or Ultra-Fast PN Rectifier diode with a Vf rating
of 1V at 10A, or better. Also, These should be placed close to their respective output pins to
maximum effectiveness.
The two bulk supply voltage capacitors, Cs, will absorb the current generated when the diodes (Do)
conduct. We recommend that a high frequency capacitor designed for low impedance and high ripple
currents be used. Tripath recommends an impedance of .1Ω or better at 100kHz and a ripple current
rating of 1Arms at 100kHz. For maximum effectiveness, Tripath recommends that these capacitors be
placed close to their respective supply pins.
20
TA2022 – KLI/1.2/07-04
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
