Tripath Technology, Inc. - Technical Information
1/2 TA2022
V5
RFBA RFBA
Processing
&
Modulation
FBKOUT1
FBKGND1
RFBC
RFBC
OUT1
OUT 1 GROUND
RFBB RFBB
AGND
Figure 2: Modulator Feedback
The modulator feedback resistors are:
RFBA = User specified, typically 1K Ω
R FBB = RFBA * VPP
(VPP - 4)
R FBC = R FBA * VPP
4
A V - MODULATOR ≈ R FBC * (R FBA + R FBB ) + 1
R FBA * R FBB
The above equations assume that VPP=|VNN|.
For example, in a system with VPPMAX=36V and VNNMAX=-36V,
RFBA = 1kΩ, 1%
RFBB = 1.125kΩ, use 1.13kΩ, 1%
RFBC = 9.0kΩ, use 9.09kΩ, 1%
The resultant modulator gain is:
AV - MODULATOR ≈ 9.09k Ω * (1.0k Ω + 1.13k Ω ) + 1 = 18.13V/V
1.0k Ω * 1.13k Ω
17
TA2022 – KLI/1.2/07-04