Digi JACKRABBIT BL1800 - Manual (Page 83)

User’s Manual 79
A
PPENDIX
C. P
OWER
M
ANAGEMENT
C.1 Power Supplies
Power is supplied to the Jackrabbit board from an external source through either header J1
or header J4. J1 is a 3-pin straight header with a pitch of 0.1". V
in
is on pin 2 between
ground on pins 1 and 3. The symmetry allows for a 3-pin cable to be connected either way.
The Jackrabbit board itself is protected against reverse polarity by a Shottky diode at D2
as shown in Figure C-1. The Shottky diode has a low forward voltage drop, 0.3 V, which
keeps the minimum DCIN required to power the Jackrabbit lower than a normal silicon
diode would allow.
Figure C-1. Jackrabbit Power Supply Schematic
The external power, +RAW, is provided to any daughterboard connected to the Jackrabbit
via pin 38 of header J4. +RAW is not protected against reversed polarity, such as could
happen if the cable was connected to header J1 offset by one pin. This absence of protec-
tion is intentional so as to provide the maximum possible voltage to any daughterboard
connected to the Jackrabbit.
Capacitor C1 provides surge current protection for the voltage regulator, and allows the
external power supply to be located some distance away from the Jackrabbit board. A
switching power supply or a linear power supply option is provided, depending on the
Jackrabbit model.
LINEAR POWER SUPPLY
POWER
IN
J1
10 µF 100 nF
330 µF
7805
LM2575
U1
U2
+RAW DCIN Vcc
Vcc
L1
C3
C2 C1
330 µH
1
2
3
1
2
3 1N5819
D2
D1
1N5819
14
15
8
1
12
7
17
18
10
2
3
4
1
SWITCHING POWER SUPPLY