STBB3J Datasheet, PDF (16/25 Pages) STMicroelectronics – 2 A, high efficiency single inductor buck-boost DC-DC converter

General description
Figure 25. Auto mode vs. output current
STBB3J
AM16845v1
7.2
External synchronization
The STBB3J implements the external synchronization function. If an external clock signal is
applied to the MODE/SYN pin with a frequency between 1.6 MHz and 2.4 MHz and with
proper low/high levels, the device automatically is in PWM mode and the external clock is
used as switching oscillator.
7.3
Enable pin
The device turns on when the EN pin is pulled high. If the EN pin is low the device stops
switching and all the internal blocks are turned off. In this condition the current drawn from
V_IN/V_INA 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; this avoids unwanted
current leakage from the input to the load.
7.4
7.4.1
7.4.2
Protection features
The STBB3J implements different types of protection features
Soft-start and short-circuit
After the EN pin is pulled high, or after a suitable voltage is applied to V_IN, V_INA and EN, the
device initiates the startup phase. The average current limit is gradually increased while the
output voltage increases. As soon as the output voltage reaches 1.0 V, the average current
limit is set to its nominal value.
Undervoltage lockout
The undervoltage lockout function prevents improper operation of the STBB3J when the
input voltage is not high enough. When the input voltage is below the VUVLO threshold, the
device is in shutdown mode. The hysteresis of 100 mV prevents unstable operation when
the input voltage is close to the UVLO threshold.
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DocID025263 Rev 5