User Manual

SDB670 – SERVICE MANUAL TNM-M-E-0032
May 13 Page 40 TECHNICAL DESCRIPTION
off by setting PWR-INH high. The radio also has the ability to power off all external devices
whilst remaining on via an FPGA software command at ACCESS-EN.
5.3.6.2 Radio Power Supplies
The unregulated 13.8 V DC input (BAT-UNSW) is routed directly to all high current devices and
also to the Main Power Switch Q901 provide BAT_SW supply for all other circuits. BAT-UNSW is
used to power the Tx PA U505, the Audio PA U808 and Ripple Filter Q1 and associated parts.
The output from Q901 feeds two dual switch-mode regulators U905A/B and U906A/B, which
provide 5.0 V, 8.0 V, 3.2 V and 1.2 V outputs respectively at high efficiency. Various protection
circuits have been included as follows:
F1 and F905 are resettable fuses protecting against excess current to accessories and radio.
U902 and U903 protect digital circuits from over-voltage transients.
D24 and U10 in conjunction with associated parts protect radio circuits from external
transients applied to the radio.
D1, D2, D3, D4, D5, D6, D8, D22, D23, D29 and D30 protect analogue circuits from over-
voltage transients.
The following is a list of the radio power supplies and the main devices and circuits they supply.
8 V Regulator U905B
Regulated 8VVCO supply:
Tx and Rx VCO’s via active filter Q600.
5 V Regulator U905A
Regulated 5VS supply:
5V-RX analogue supply via Q915 to Rx front-end, IF Amplifier, T/R switch, Loop Filter.
5V-TX analogue supply via Q918 to Tx buffers, VCO switch.
5V-RF analogue supply to U400, U500, U502, U700, VCO buffers, VCO Varactor Reference
Supply, TCXO.
5VD digital supply via L915 to U11, U12, Q800.
5VA analogue supply via L915 and L919 to audio circuits including U804, U805, U806.
3V2A low noise regulated supply via U910 to U401, U503, U701, U719, U803 via L801, RX-
TUNE controls and varactor bias.
Various switching functions.
3.2 V Regulator U906A
Regulated 3.2 V supply (3V2S):
3V2AD reference supply via L931A to ADC U401.
3V2D digital supply via L931 to U201, U202, U203, U204, U205, U208, U300, U302, U307.
1V8 digital supply via regulator U911 to CODEC U803, Cellular RAM U304 and FPGA
U300D.
2V5D digital supply via regulator U909 and L929 to FPGA U300C.