After Sales
Technical Documentation
RAE/RAK–1N
PDA Hardware
Page 6 – 39
Original, 08/96
PDAPWRU
Technical Description
The power block creates supply voltages for the PROCU and LCDM,
generates reset signal for CPU and contains LCD contrast control and
enable circuits. Input filter is required to reduce input noise of switching
regulators. Back–up battery keeps RTC alive when main battery is not
connected. System voltage is present allways until battery voltage drops
below 5.0V.
Figure 9. PDAPWRU block diagram
VBATT
3.3V 500mA current mode buck
regulator, internal switch transistor
5V 50mA low drop–out linear regulator
21V 6mA SMPS including output voltage
adjustment by LCDPWM signal and tem-
perature compensation
Reset circuit
Undervoltage lockout
VSYS
VCC5
LCDVEE
PWRGOOD
LCDVEEON
LCDPWM
3V backup battery
VBACK
5VPDX
LCDVCC
LCDVCCON LCD Vcc switch circuit
Table 23. External Signals and Connections, Inputs
Signal Name Signal description From (1)
LCDVCCON LCD Vcc on/off PROCU
LCDVEEON LCD Vee on/off PROCU
LCDPWM PWM signal for LCD voltage control PROCU
5VPDX 5V regulator powerdown PROCU
VB Battery voltage B2B / VB
Note 1. B2B = Board to board connector between PDA and CMT modules
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