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LT1313
OPERATION
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The LT1313 is two programmable output voltage, low-
dropout linear regulators designed specifically for PCMCIA
VPP drive applications. Input power is typically obtained
from a loosely regulated input supply between 13V and
20V. The LT1313 consists of the following blocks:
Two Low Dropout Voltage Linear Regulators: The heart
of the LT1313 is two PNP-based low-dropout voltage
regulators which drop the unregulated supply voltage
from 13V to 20V down to 12V, 5V, 3.3V, 0V or Hi-Z
depending upon the state of the four Enable inputs and the
two V
CC
Sense inputs. The regulators have built-in current
limiting and thermal shutdown to protect the device, the
loads, and the sockets against inadvertent short circuiting
to ground.
Voltage Control Logic: The two VPP
OUT
outputs have five
possible output modes: 0V, 3.3V, 5V, 12V and Hi-Z. These
five modes are selected by the four Enable inputs and the
two V
CC
Sense inputs as described by the Truth Table.
V
CC
Sense Comparators: When the V
CC
mode is selected,
the LT1313 automatically adjusts each regulated VPP
output
voltage to 3.3V or 5V depending upon the voltage present
at the corresponding PC card V
CC
supply pin. The thresh-
old voltage for these comparators is set at 4V and there is
approximately 50mV of hysteresis provided to ensure
clean switching between 3.3V and 5V.
VPP
VALID Comparator: Two voltage comparators moni-
tor each output voltage when the 12V mode is selected and
are driven low when the output is in regulation above 11V.
These two outputs function separately.
AEN0 AEN1 ASENSE AVPP
OUT
AVALID
00 X 0V 1
1 0 X 12V 0
0 1 3.0V to 3.6V 3.3V 1
0 1 4.5V to 5.5V 5V 1
1 1 X Hi-Z 1
X = Don’t Care
LT1313 Truth Table
BEN0 BEN1 BSENSE BVPP
OUT
BVALID
00 X 0V 1
1 0 X 12V 0
0 1 3.0V to 3.6V 3.3V 1
0 1 4.5V to 5.5V 5V 1
1 1 X Hi-Z 1
Note: Each channel is independently controlled.
The LT1313 is two voltage programmable linear regula-
tors designed specifically for PCMCIA VPP driver applica-
tions. The device operates with very low quiescent current
(60µA) in the 0V and Hi-Z modes of operation. In the Hi-Z
mode, the output leakage current falls to 1µA. In addition
to the low quiescent currents, the LT1313 incorporates
several protection features which make it ideal for PCMCIA
applications. The LT1313 has built-in current limiting
(330mA) and thermal shutdown to protect the device and the
socket VPP pins against inadvertent short-circuit conditions.
Output Capacitance
The LT1313 is designed to be stable with a wide range of
output capacitors. The minimum recommended value is a
1µF with an ESR of 3Ω or less. The capacitor is connected
directly between the output pin and ground. For applications
where space is very limited, capacitors as low as 0.33µF can
APPLICATIONS INFORMATION
WUU
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be used. Extremely low ESR ceramic capacitors with values
less than 1µF must have a 2Ω resistor added in series with
the output capacitor.
Transient and Switching Performance
The LT1313 is designed to produce minimal overshoot
with capacitors in the range of 1µF to 10µF. Larger
capacitor values can be used with a slowing of rise and
fall times.
The positive output slew rate is determined by the 330mA
current limit and the output capacitor. The rise time for a
0V to 12V transition is approximately 40µs and the rise
time for a 10µF capacitor is roughly 400µs (see the
Transient Response curves in the Typical Performance
Characteristics section).
