LT1313
OPERATION
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.
LT1313 Truth Table
AEN0
AEN1
ASENSE
AVPP
OUT
AVALID
APPLICATIONS INFORMATION
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
(60碌A(chǔ)) in the 0V and Hi-Z modes of operation. In the Hi-Z
mode, the output leakage current falls to 1碌A(chǔ). 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
1碌F with an ESR of 3鈩?or less. The capacitor is connected
directly between the output pin and ground. For applications
where space is very limited, capacitors as low as 0.33碌F can
be used. Extremely low ESR ceramic capacitors with values
less than 1碌F must have a 2鈩?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 1碌F to 10碌F. 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 40碌s and the rise
time for a 10碌F capacitor is roughly 400碌s (see the
Transient Response curves in the Typical Performance
Characteristics section).
6
U
W
U
U
U
0
1
0
0
1
X = Don鈥檛 Care
0
0
1
1
1
BEN1
X
X
3.0V to 3.6V
4.5V to 5.5V
X
BSENSE
0V
12V
3.3V
5V
Hi-Z
BVPP
OUT
1
0
1
1
1
BVALID
BEN0
0
1
0
0
1
0
0
1
1
1
X
X
3.0V to 3.6V
4.5V to 5.5V
X
0V
12V
3.3V
5V
Hi-Z
1
0
1
1
1
Note: Each channel is independently controlled.
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