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A
PPENDIX
Appendix E describes the power circuitry provided on the
LP3500. The LP3500 can operate from an unregulated external
power source, or from an external battery. There is onboard bat-
tery backup for the SRAM and the real-time clock.
E.1 External Power Supply
Power is normally supplied to the LP3500 via pins 16 and 17 of header J2 on the LP3500.
The Prototyping Board provides a convenient header plug for use with the AC adapter
included with the LP3500 Tool Kit. The Prototyping Board includes a Shottky diode for
protection against reverse polarity.
The raw DC power, VIN, goes through a linear regulator as shown in Figure E-1. The lin-
ear regulator outputs a Vcc of 2.8 V DC.
J2
VIN
16
17
PF7
The power necessarily dissipated by the regulator can be calculated if both the external
input voltage and the current drawn by the LP3500 are known. The current provided by
the high-power output drivers does not have to be included if a separate power supply is
connected to K so that power does not come from Vcc.
User's Manual
E. P
R51
C65
105 kW
47 µF
R58
220 kW
Q20
Figure E-1. LP3500 Linear Regulator Circuit
M
OWER
ANAGEMENT
LINEAR POWER SUPPLY
MIC5236
U13
3
2
1
4
26.1 kW
Q18
C70
100 nF
Vcc
C64
R52
10 µF
R53
20 kW
R57
PB0
220 kW
119
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