7
LTC1710
OPERATIO
U
until about 300µs after V
CC
crosses the undervoltage
lockout threshold (typically 2V). The circuit includes some
hysteresis and delay to avoid nuisance resets. Once opera-
tion begins, V
CC
must drop below the threshold for at least
100µs to trigger another POR sequence.
Input Threshold
Anticipating the trend of lower and lower supply voltages,
the SMBus is specified with a V
IH
of 1.4V and a V
IL
of 0.6V.
While some SMBus parts may violate this stringent SMBus
specification by specifying a higher V
IH
value for a corre-
sponding higher input supply voltage, the LTC1710 meets
and maintains the constant SMBus input threshold speci-
fication throughout the entire supply voltage range of 2.7V
to 5.5V.
Thermal Shutdown
In the unlikely event that either power switch overheats, a
thermal shutdown circuit, which is placed closely to the
two switches, will activate and turn off the gate drives to
both switches. The thermal shutdown circuit has a thresh-
old of 120°C with a 15°C hysteresis.
Figure 3. Low Dropout Regulator Switching a 3.3V/300mA Supply
Figure 4. The LTC1710 Switching Two Different Voltage Loads
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
Charge Pump
To fully enhance the internal N-channel power switches,
an internal charge pump is used to boost the gate drive to
a maximum of 6V above V
CC
. The reason for the maximum
charge pump output voltage limit is to protect the internal
switches from excessive gate overdrive. A feedback net-
work is used to limit the charge pump output once it is 6V
above V
CC
. To prevent the power switches from turning on
too fast, an internal current source is placed between the
output of the charge pump and the gate of the power
switch to control the ramp rate.
Since the charge pumps are driving just the gates of the
internal switches, only a small amount of current is
required. Therefore, all the charge pump capacitors are
integrated onboard. The drain of switch 1 is internally
connected to V
CC
, however, the drain of switch 0 is user
controlled through Pin 1. In other words, SMBus devices
using different power supply voltages can be simulta-
neously switched by the same LTC1710.
Power-On Reset and Undervoltage Lockout
The LTC1710 starts up with both gate drives low. An
internal power-on reset (POR) signal inhibits operation
TYPICAL APPLICATIONS
U
The LTC1710, when used with the LT
®
1521-3.3, can
switch a regulated 3.3V/300mA supply to a load (Figure 3).
Also, with the help of the LT1304-5, the LTC1710 can be
used to make a boost switching regulator with output
disconnect and a low standby current of 22µA (Figure 5).
81
2
10µF10µF
7
5
6
FROM SMBus
3
PROGRAMMABLE
4
1710 F04
V
CC
SW0D
5V
3.3V
CLK
DATA
OUT0
LTC1710
OUT1
AD1
GND
3.3V
LOAD
5V
LOAD
8
7
1
10µF
1µF
2
5
6
8
5
1
2
FROM SMBus
3
PROGRAMMABLE
4
1710 F03
V
CC
SW0D
5V
CLK
DATA
SWITCHED
3.3V
OUT1
LTC1710
V
IN
SHDN
V
OUT
SENSE
LT1521-3.3
OUT0
AD1
GND
1.5µF
3.3V
