LTC1475CMS8-5 Linear Technology, LTC1475CMS8-5 Datasheet - Page 11

• Manufacturer Part Number: LTC1475CMS8-5
• Description: IC DC/DC CONV STEP-DOWN 8-MSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1475CMS8-5

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 5V
• Current - Output: 750mA
• Voltage - Input: 3 ~ 18 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Frequency - Switching: -

APPLICATIONS
LTC1475 Pushbutton On/Off and
Microprocessor Interface
The LTC1475 provides pushbutton control of power on/off
for use with handheld products. A momentary ground on
the ON pin sets an internal S/R latch to run mode while a
momentary ground on the LBI/OFF pin resets the latch to
shutdown mode. See Figure 6 for a comparsion of on/off
operation of the LTC1474 and LTC1475 and Figure 7 for a
comparison of the circuit implementations.
In the LTC1475, the LBI/OFF pin has a dual function as
both the shutdown control pin and the low battery com-
parator input. Since the “OFF” pushbutton is normally
open, it does not affect the normal operation of the low
battery comparator. In the unpressed state, the LBI/OFF
input is the divided down input voltage from the resistive
divider to the internal low battery comparator and will
normally be above or just below the trip threshold of
1.23V. When shutdown mode is desired, the LBI/OFF pin
is pulled below the 0.7V threshold to invoke shutdown.
The ON pin has precedence over the LBI/OFF pin. As seen
in Figure 6, if both pins are grounded simultaneously, run
mode wins.
Figure 18 in the Typical Applications section shows an
example for the use of the LTC1475 to control on/off of a
microcontroller with a single pushbutton. With both the
microcontroller and LTC1475 off, depressing the
pushbutton grounds the LTC1475 ON pin and starts up the
LTC1475 regulator which then powers up the microcon-
troller. When the pushbutton is depressed a second time,
LTC1474
LTC1475
Figure 6. Comparison of LTC1474 and LTC1475
Run/Shutdown Operation
LBI/OFF
MODE
MODE
RUN
ON
U
RUN
RUN
INFORMATION
U
SHUTDOWN
SHUTDOWN
W
ON OVERRIDES LBI/OFF
WHILE ON IS LOW
RUN
RUN
U
1474/75 F06
the depressed switch state is detected by the microcon-
troller through its input. The microcontroller then pulls the
LBI/OFF pin low with the connection to one of its ouputs.
With the LBI/OFF pin low, the LTC1475 powers down
turning the microcontroller off. Note that since the I/O pins
of most microcontrollers have a reversed bias diode
between input and supply, a blocking diode with less than
1 A leakage is necessary to prevent the powered down
microcontroller from pulling down on the ON pin.
Figure 19 in the Typical Applications section shows how to
use the low battery comparator to provide a low battery
lockout on the “ON” switch. The LBO output disconnects
the pushbutton from the ON pin when the comparator has
tripped, preventing the LTC1475 from attempting to start
up again until V
Absolute Maximum Ratings and Latchup Prevention
The absolute maximum ratings specify that SW (Pin 5) can
never exceed V
situation should never occur. It could, however, if the
output is held up while the supply is pulled down. A
condition where this could potentially occur is when a
battery is supplying power to an LTC1474 or LTC1475
regulator and also to one or more loads in parallel with the
the regulator’s V
LTC1474 or LTC1475 regulator is supplying a light load
and one of the parallel circuits is a heavy load, the input
capacitor of the LTC1474 or LTC1475 regulator could be
pulled down faster than the output capacitor, causing the
absolute maximum ratings to be exceeded. The result is
often a latchup which can be destructive if V
Battery disconnect is possible as a result of mechanical
stress, bad battery contacts or use of a lithium-ion battery
RUN
100k
Figure 7. Simplified Implementation of
LTC1474 and LTC1475 On/Off
IN
RUN
IN
IN
LTC1474
(Pin 7) by more than 0.3V. Normally this
. If the battery is disconnected while the
is increased.
LTC1474/LTC1475
ON
OFF
100k
V
IN
IN
is reapplied.
ON
LBI/OFF
LTC1475
11
1474/75 F07