LTC3427_15 Datasheet, PDF (9/12 Pages) Linear Technology – 500mA, 1.25MHz Synchronous Step-Up DC/DC Converter in 2mm 2mm DFN Package

LTC3427
APPLICATIO S I FOR ATIO
V_IN > V_OUT Operation
The LTC3427 will maintain voltage regulation when the
input voltage is above the output voltage. This is achieved
by terminating the switching of the synchronous P-chan-
nel MOSFET and applying V_IN statically on its gate. This
will ensure the volt • seconds across the inductor reverse
during the time current is flowing to the output. Since this
mode will dissipate more power in the LTC3427, the
maximum output current is limited in order to maintain an
acceptable junction temperature and is given by:
I_OUT(MAX)
=
85
•
125 – T_A
⎡⎣(V_IN + 1.5) –
V_OUT
⎤⎦
where T_A = ambient temperature.
For example at V_IN = 4.5V, V_OUT = 3.3V, and T_A = 85°C, the
maximum output current is 145mA.
Short-Circuit Protection
The LTC3427 output disconnect feature allows output
short circuit while maintaining a maximum internally set
current limit. However, the LTC3427 also incorporates
internal features such as current limit foldback and ther-
mal shutdown for protection from an excessive overload
or short circuit. During a prolonged short circuit the
current limit folds back to a typical value of approximately
400mA should V_OUT drop below 950mV. This 400mA
current limit remains in effect until V_OUT exceeds approxi-
mately 1V, at which time the nominally internally set
current limit is restored.
3427fa
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