Power-Up/Power-Down Sequence; Figure 3-45. Power-On Reset Circuit - Motorola ASTRO XTL 1500 Detailed Service Manual

Theory of Operation: Controller Section
SW_B+
Soft_Turn_Off
Emergency
SW_A+
SW_B+
5V
4.2V
Detector
U05
The SW_B+ and A+ voltage levels are sensed by the comparator circuit consisting of U0604, Q0505,
and R0505, R0506, R0508, and R0509. When SW_B+ goes below 8.5 V or SW_A+ goes below
10 V, U0604-7, SW B+ Sense, goes low. When this occurs, the radio completes its soft power-down
and eventually drives the Soft_Turn_Off line low, which turns off Q0502 and FET Q0503. This turns
off SW_A+ and eventually turns off the 9-V, 5-V, 3-V, 2.85-V, 1.85-V, and 1.55-V regulators.
The POR* circuit consists of a wired-OR circuit of the error output lines from the 2.85-V, 1.85-V, and
1.55-V regulators, which indicates a failure of either of these regulators; and a reset output from a
4.2-V detector IC U0504. When either of the regulators fails or the 5-V supply begins to drop below
4.2 V, POR* is asserted low, resetting the microprocessor U100 at U001, LV_DETECT.
When the radio is operating correctly (A+ > 10 V and SW_B+ > 8.5 V), SW_A+ and VOCON
regulators U0501, U0502, and U05007 are at normal voltage. The POR* line and SW_B+_Sense are
high (2.85 V).
The other signal that can cause a processor/radio reset is the SB9600 RESET line. The RESET line
is driven high (5 V) by a remote device that is having problems communicating with the processor.

3.14.4 Power-Up/Power-Down Sequence

The XTL 1500 radio power is cycled via SW_B+ (battery voltage level). This voltage is supplied by
the control head via J0401, pin 17, when the On/Off knob is cycled.SW_B+ is derived from the
battery A+ voltage via a power FET in the control head.
6815854H01-A
Q0505
U0604
+
SWB+ _Sense
-
2.85V 1.85V
Reg. Out Reg. Out
U0501 U0507

Figure 3-45. Power-On Reset Circuit

A+
FET
B+_CNTL
To Microprocessor
2.85V
(LV_DETECT)
1.55V
Reg. Out
U0502
SW_A+
To 9.3V Regulators
(U0500......)
POR
To Microprocessor
MAEPF-27826-O
June 15, 2005
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