STBB1-AXX Datasheet, PDF (12/24 Pages) STMicroelectronics – Buck-boost DC-DC converter

Detailed description
6.3
External synchronization
STBB1-AXX
The STBB1-AXX implements the external synchronization pin. If an external clock signal is
applied to the MODE (SYN) pin with a frequency between 1.35 MHz and 2.0 MHz and with
proper low/high levels, the device automatically goes to PWM mode and the external clock
is used as switching oscillator.
6.4
Enable pin
The device operates when EN pin is set high. If EN pin is set low the device stops
switching, all the internal blocks are turned off. In this condition, the current drawn from
VIN/VINA is below 1 µA in the whole temperature range. In addition, the internal switches
are in off-state so the load is electrically disconnected from the input, by avoiding unwanted
current leakage from the input to the load.
6.5
6.5.1
6.5.2
6.5.3
Protection features
The STBB1-AXX implements different types of protection features.
Soft-start and short-circuit
After EN pin is pulled high, or after a suitable voltage is applied to VIN, VINA and EN, the
device initiates the start-up phase. The average current limit is set to 400 mA at the
beginning and gradually rises while the output voltage increase is being tracked. As soon
the output voltage reaches 1.0 V the average current limit is set to its nominal value.
This method allows a current limit proportional to the output voltage. If there is a short in
the V_OUT pin, the output current doesn’t exceed 400 mA.
This process is not handled by a timer so the device is also able to start even with large
capacitive loads.
Undervoltage lockout
The undervoltage lockout function prevents improper operation of the STBB1-AXX when
the input voltage is not high enough. When the input voltage is below VUVLO threshold the
device is in shutdown mode. The hysteresis of 100 mV prevents unstable operation when
the input voltage is close to UVLO threshold.
Overtemperature protection
An internal temperature sensor continuously monitors the IC junction temperature. If the IC
temperature exceeds 140 °C typically the device stops operating. As soon as the
temperature falls below 120 °C typically normal operation is restored.
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