Datasheet

LT8705
19
8705fb
For more information www.linear.com/LT8705
operaTion
When the input or output current causes the respective
IMON_IN or IMON_OUT voltage to rise near or above
1.208V (typical), the V
C
pin voltage will be pulled down to
maintain the desired maximum input and/or output current
(see EA1 and EA2 on the Block Diagram). The input current
limit function prevents overloading the DC input source,
while the output current limit provides a building block
for battery charger or LED driver applications. It can also
serve as short-circuit protection for a constant-voltage
regulator. See the Applications Information section for more
information about setting up the current regulation loops.
SRVO Pins
The QFN package has four open-drain SRVO pins:
SRVO_FBIN, SRVO_FBOUT, SRVO_IIN, SRVO_IOUT.
Pl
ac
e pull-up resistors from the desired SRVO pin(s) to a
power supply less than 30V (i.e., the LDO33 pin) to enable
reading of their logic states. The SRVO_FBOUT, SRVO_IIN
and SRVO_IOUT pins are pulled low when their associ
-
ated error amp (EA4, EA2, EA1) input voltages are near
o
r g
reater than their regulation voltages (≅1.2V typical).
SRVO_FBIN is pulled low when FBIN is near or lower than
its regulation voltage (≅1.2V typical). The SRVO pins can
therefore be used as indicators of when their respective
feedback loops are active. For example, the SRVO_FBOUT
pin pulls low when FBOUT rises to within 29mV (typical, see
Electrical Characteristics) of its regulation voltage (1.207V
typical). The pull-down turns off after FBOUT falls to more
than 44mV (typical) lower than its regulation voltage.
As another example, the SRVO_IOUT pin can be read to
determine when the output current has nearly reached its
predetermined limit. A logic “1” on SRVO_IOUT indicates
that the output current has not reached the current limit
and a logic “0” indicates that it has.
CLKOUT and Temperature Sensing
The CLKOUT pin toggles at the LT8705’s internal clock
frequency whether the internal clock is synchronized to an
external source or is free-running based on the external R
T
resistor. The CLKOUT pin can be used to synchronize other
devices to the LT8705’s switching frequency. Also, the duty
cycle of CLKOUT is proportional to the die temperature
and can be used to monitor the die for thermal issues.