Voltage Regulators - Motorola TDMA M3090 Service Manual

TDMA M3090/M3097:
BATT_SAV
2.75V
5V
VDOUB
Description
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 produ ced 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 thr ough 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 ver sa.
U1420 is the negative supply generator. It is used to supply -5V to the an tenna 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 b y CR1420 causing a -10Vdc out put.

Voltage Regulators

Q1571
Q1570
U1420
C1421
U1560
CR1560
CR1420
-5V
-10V
2.75V