Motorola M3097 Service Manual Page 111

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TDMA M3090/M3097: Voltage Regulators
B28
Description
BATT_SAV
2.75V
5V
-5V
-10V
Q1571
Q1570
CR1420
U1420
VDOUB
CR1560
U1560
2.75V
There are some circuits that require a voltage higher than the battery source. For this reason, a voltage doubling charge pump circuit is provided. U1560 takes the 2.75V
source and oscillates it with a high peak to peak signal. The positive region of the signal is then sent out to produced the VDOUB supply.
BATT_SAV is used to cut off the -5V supply to the antenna switching circuitry to save battery power. When the BATT_SAV line is on (high), Q1571 switches off, not
allowing 2.75V to go through it. This causes a low state at Q1570 causing it to switch off, not allowing the -5V to get to the antenna switchin g circuitry and vise versa.
U1420 is the negative supply generator. It is used to supply -5V to the antenna switching circuitry and -10V to the display contrast circuitry.
The +5Vp-p square wave output from U1420 gets shifted to -5Vp-p square wave with a -5V reference at CR1420. This shift in reference at CR1420 is caused by -5Vdc
output of U1420. The produced squarewave is then rectified by CR1420 causing a -10Vdc output.
C1421
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