E.F. Johnson Company 5100 ES, Service Manual

Page: 64 / 180

5-20 5100 ES Series Portable Radio Service Manual January 2007
Circuit Description
5.5.1.1 Digital
Four regulators provide power to the digital electronics on the UI and Logic boards. These
voltages are as follows:
• 5Vdc (U11) – power for keypad backlights, LCD backlights, and transmit/receive LED
• 1.6Vdc(U49) – Logic Board DSP and SEM processor core voltage supply
• 1.8Vdc(U46) – Logic Board Codec and CPLD core voltage supply/UI board MPC870
and CPLD core voltage
• 3.3Vdc(U47) – Supply for digital I/O and discrete logic devices
The supplies are powered up in the following sequence, 1.6Vdc, 1.8Vdc, 3.3Vdc, then
5Vdc. This power up sequence is dictated by power application requirements of the DSP
and MPC 870 processors. Additionally, the switching regulators (U49, U46, and U47) are
synchronized to a 768Khz clock from the CPLD (U20) that is derived from the 12.288
TCXO (Y2).
5.5.1.2 Analog
Two linear regulators (U11, U45) provide power to the analog circuitry (op amps, Codec)
on the Logic and UI boards. The 5Vdc analog supply (U11) powers the audio out section
(U9, U10) and Codec 3.3Vdc linear regulator (U45) on the Logic Board. Additionally, the
5Vdc supply provides power to the microphone and audio output circuitry on the UI
Board.
5.5.1.3 RF Deck
Two linear regulators supply 3.3Vdc and 5.5Vdc voltages to the RF Deck. The 3.3Vdc
supply (U43) powers the digital circuitry on the RF Deck. The 5.5Vdc supplies power to
the 5Vdc LDOs used on the RF Deck.
5.5.2 DSP
The Digital Signal Processing (DSP) functions are performed by a TI 5510 DSP (U15) and
the TI AIC21 Codec (U27) with the support of MPC870 processor on the UI board.
Operation of the DSP is described in the paragraphs below.