LT8705
OPERATION
When the input or output current causes the respective
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
pinpullslowwhenFBOUTrisestowithin29mV(typical,see
ElectricalCharacteristics)ofitsregulationvoltage(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.
IMON_IN or IMON_OUT voltage to rise near or above
1.208V (typical), the V pin voltage will be pulled down to
C
maintainthedesiredmaximuminputand/oroutputcurrent
(seeEA1andEA2ontheBlockDiagram).Theinputcurrent
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.SeetheApplicationsInformationsectionformore
information about setting up the current regulation loops.
SRVO Pins
CLKOUT and Temperature Sensing
The QFN package has four open-drain SRVO pins:
SRVO_FBIN, SRVO_FBOUT, SRVO_IIN, SRVO_IOUT.
Place pull-up resistors from the desired SRVO pin(s) to a
power supply less than 30V (i.e., the LDO33 pin) to enable
readingoftheirlogicstates.TheSRVO_FBOUT,SRVO_IIN
and SRVO_IOUT pins are pulled low when their associ-
ated error amp (EA4, EA2, EA1) input voltages are near
or greater than their regulation voltages (≅1.2V typical).
SRVO_FBIN is pulled low when FBIN is near or lower than
The CLKOUT pin toggles at the LT8705’s internal clock
frequencywhethertheinternalclockissynchronizedtoan
externalsourceorisfree-runningbasedontheexternalR
resistor.TheCLKOUTpincanbeusedtosynchronizeother
devicestotheLT8705’sswitchingfrequency.Also,theduty
cycle of CLKOUT is proportional to the die temperature
and can be used to monitor the die for thermal issues.
T
8705p
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