Portable
PLUS
Computer
Functional
Description
5·15
When
the
computer is in sleep mode,
the
operation of
the
VCC regulator
shutdown
circuitry
must
be
disabled.
When
SLEEP is high, A2Q52
turns
on,
which
turns
on
A2Q53, which in
turn
clamps off
A2Q56. Even
if
PLUGINl*
or
PLUGIN2*
become ungrounded, A2Q56 will
not
turn
on
while
A2Q53 is
on
, so VCC regulator
shutdown
does
not
occur.
Transistor A2Q83 provides
the
CARDSIN*
output
to the PPU circuitry.
When
there are cards in-
stalled in
both
plug-in slots,
the
gate of A2Q83 is pulled
up
to
VBAT
by
A2R66 (pins 7
and
8)
and
A2R65 (or A2Q53,
if
on). This
turns
on
A2Q83, which pulls CARDSIN* to
ground
, which can
be
detected by the PPU.
If
a card is removed from either plug-in slot, A2Q54 or A2Q55
turns
on, grounding
the
gate
of
A2Q83
and
turning it off. CARDSIN*
then
becomes a high impedance, which is also detectable
by
the
PPU
.
A2Q64 is biased
on
by
resistors A2R63 (pins 7
and
8)
and
A2R66 (pins 5
and
6)
if
the
difference
in
voltage between
VBAT
and
VCCDS is
O.8V
or more.
When
A2Q64 is
on
it turns
on
A2Q84,
which
grounds LOW
BATTERY,
indicating to
the
PPU that the battery is
not
low.
When
the difference between
VBAT
and
VccDS is less
than
O.8V,
A2Q64
turns
off, allowing A2R66
(pins 3
and
4)
to
turn
off A2Q84, making LOW
BATTERY
a high impedance.
The
LOW
BATTERY
output
indicates that
the
battery is low
when
VBAT
is less
than
5.8V. The circuit
compares
VBAT
to VccDS, so it works properly only while the computer is in awake
mode
.
The
SHUTDOWN
output
circuit is comprised of A2Q65, A2R117, A2R86, A2R66 (pins 1
and
2),
and
A2Q85. It works in the same fashion as the LOW
BATTERY
ouput
circuit, except it is designed to
switch
at
a voltage difference of O.
6V
between
VBAT
and
VccDS.
The reference voltage
VREF
is
provided
by
A2VRSO
. Bias current is provided
by
A2R69 from
VBAT.
When
the
computer is awake,
the
LCD negative supply circuitry loads
VREF,
so additional bias current
is provided through A2CR63
and
A2R70.
5.15.2
Battery
The
6-volt (nominal), three-cell, lead-acid battery
has
its electrolyte completely enclosed in
the
battery
case, eliminating leakage
under
normal conditions.
When
fully charged, the battery
has
21f2
ampere
-
hours
of stored power
and
a
large
short-circuit
capacity.
5.15.3
Battery
Charger
The
function
of
the
battery charger circuit is to convert the ac
output
of
the
recharger to a tempera-
ture-compensated dc charge voltage for the battery.
The
battery charger circuit can actually regulate
at
two different voltage levels.
One
level is float voltage, which is the voltage
which
is
applied
to
the
battery
after it is fully charged. This voltage is selected to maximize
the
life of
the
battery
and
varies
with temperature. At
25°C
it
is 7.
0SV
± 2%. The
other
voltage level is overcharge voltage,
higher
than
float voltage,
and
applied to
the
battery for a limited time during each charge cycle to reduce
overall charge time. This voltage level is
about
7.5V at 25°C.
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