Power Supply Circuit; Low Battery Warning; Dsp - Kenwood NX-5400 Service Manual

2.4.6.5

Low Battery Warning

The battery voltage is divided using R40 and R41 and is detected by A/D converter (IC900). When the battery voltage falls below the
voltage set by the Low battery warning adjustment, the red LED blinks to notify the operator that it is time to replace the battery. If the
battery voltage falls even more (approx. 5.8V), a beep sounds and transmission stops.
Low battery warning
The red LED blinks during transmission.
The red LED blinks and the warning tone
beeps while the PTT switch is pressed.
Low battery warning
The red LED blinks during transmission.
The red LED blinks and the warning tone beeps while the PTT switch is pressed.
Battery condition
The battery voltage is low but the transceiver is still usable.
The battery voltage is low and the transceiver is not usable to make calls.
2.4.6.6

DSP

The DSP circuit consists of a MPU/DSP (IC702) and processes the baseband signal. The DSP operates at 288MHz (MAX) clock, the
I/O section operates at 3.3V/1.8V and the core section operates at 1.2V.
The DSP carries out the following processes:
• 4 Level FSK processing
• Analog FM pre-emphasis/de-emphasis
• Vocoder processing between audio codec and modulation/demodulation
• CAI processing, such as error correction encoding
• QT/DQT encoding/decoding
• DTMF encoding/decoding
• MSK encoding/decoding
• 2-tone encoding/decoding
• Compressor/expander processing
• Voice scrambler processing
• Transmit/receive audio filtering processing
• Microphone amplifier AGC processing
• Audio mute processing
• Modulation level processing
• Active Noise Reduction
• Voice recording/playback processing
• Voice announce processing

2.4.7 Power Supply Circuit

The battery voltage (+B) is provided from battery terminal. The battery voltage passes through the 3.15A fuse (F1), and goes to RF
final amplifier, AVR ICs (IC31, IC82, IC801, IC36, IC63, IC65, IC64), DC/DC converter (IC33), transistor (Q32, Q71 through the 1A
fuse (F2)), and voltage detector IC (IC20). Voltage detector (IC20) watches battery voltage. If the battery voltage is enough higher
than 5.6V, detector outputs High. Then, IC31 (31BU) outputs 3.1V, and IC32 (12BU) outputs 1.2V, and Q31 is turned on.
When the VOL SW is turned on, SB1 becomes high (battery voltage). The DC/DC (IC33) operates if both SB1 and output of detector
are high. IC33 (38M) outputs 3.8V, and A30 (12M) outputs 1.2V. Then, IC34 (18M) and IC37 (18BT) outputs 1.8V. Then, IC80 (30M)
outputs 3.0V, and IC38 (33BT) and IC35 (33M) and IC81 (33OPT) outputs 3.3V. Then, IC39 (33A) outputs 3.3V, and IC82 (50A) out-
puts 5.0V. Then, IC701 (18M_3) outputs 1.8V, and Q71 (53AF) is turned on. Voltage detector (IC704) watches IC33 (38M) output
voltage. If the 38M output voltage is enough higher than 3.5V, detector outputs High. As a result, the MPU/DSP operate.
The SBC signal becomes High after the MPU/DSP operates, and IC61 (33C), IC36 (50C), IC63 (50VCO) and Q32 (SB2) are turned on.
When SD_EN signal becomes High, IC30 (33SD) operates. When 5UC signal becomes High, IC801 (50U) operates. When TXC signal
becomes High, IC65 (50T) operates. IC65 (50T) is turned on in transmit mode.
When RXC signal becomes High, IC64 (50R) operates. IC64 (50R) is turned on in receive mode. Switches are controlled by the MPU/
DSP.
When the VOL SW is turned off /PSW signal becomes Low. After detecting /PSW signal, the MPU/DSP changes SBC signal to Low.
The 50C is fed to IC60 (200C). IC60 (200C) is the DC/DC boost converter. IC60, D60, C64 consist of a voltage quadruple. The 200C
circuit then outputs approximately +20VDC.
1-14 (No.RA016<Rev.001>)
Battery condition
The battery voltage is low but the transceiver is still usable.
The battery voltage is low and the transceiver is not usable to
make calls.