Datasheet

LXDC3EP series
Micro DC-DC converter
8
Dec 2014
Power-Save mode at light load PWM mode at heavy load
Nominal output voltage
7. Detailed Description
Power-Save Mode / Forced PWM Mode
The MODE pin allows selecting the operating mode. If the MODE pin is pulled to logic low voltage (MODE-L), the
converter operates automatic pulse-skip and PWM mode. In this mode, the converter operates pulse-skip mode
at light load current, and when the load current increases, the operating mode will changes
to PWM mode
automatically. In this mode, the converter can work in high efficiency over wide load current range. The transition
current between PFM and PWM is depend on Vin, Vout and other factors, but the ballpark threshold is about
50-200mA
If the MODE pin is pulled to logic high voltage (MODE-H), the device operates in Forced PWM mode. In this mode,
the converter operates in PWM mode even at light load current. The advantage of this mode is that the converter
operates with a fixed frequency that allows simple filtering of switching frequency. In this mode, the efficiency is
lower compared to the PFM mode at light load current.
UVLO (Under Voltage Lock Out)
The input voltage (Vin) must reach or exceed the UVLO voltage (2.2Vtyp) before the device begins the start up
sequence even when EN pin is kept high. UVLO function keeps away of an unstable operation at low Vin range
Soft Start
The device has an internal soft-start function that limits the inrush current during start-up. The soft-start system
progressively increases the switching on-time from a minimum pulse-width to that of normal operation. Because
of the function, the output voltage increases gradually from zero to nominal voltage at start-up event. The nominal
soft-start time is 170usec.
Enable
The device starts operation when EN is set high and starts up with a soft start. For proper operation, the EN pin
must be terminated to logic high and must not be left floating. Pulling the EN pin to logic low forces the device to
shutdown.
Over Current Protection
When the output current reaches the OCP threshold, the device narrows the switching duty and decrease the
output voltage. When the current goes below the threshold, the converter returns to normal operation
automatically.
Thermal Shutdown
The device has a thermal overload protection function. When the internal IC’s junction temperature exceeds
around 150
o
C, the device goes into thermal shutdown. The device returns to its normal operation when the
Internal IC’s junction temperature falls below 130
o
C (typ). For reliable operation, the IC temperature should be
kept below 125
o
C. Prolonged thermal overload condition may damage the device