General description

STBB3JCC

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DocID025425 Rev 5

Figure 29. Auto mode vs. output current

7.2

External synchronization

The STBB3JCC 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

in off-state so the load is electrically disconnected from the input; this avoids unwanted

current leakage from the input to the load. The EN pin can be used as dimming function by

applying a square waveform from100 to 300 Hz.

7.4

Protection features

The STBB3JCC implements different types of protection features.

7.4.1

Soft-start and overcurrent

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.

7.4.2

Undervoltage lockout

The undervoltage lockout function prevents improper operation of the STBB3JCC when the

input voltage is not high enough. When the input voltage is below the UVLO 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.

AM16845v1