Detailed description

STBB1XX

10/21

Doc ID 15474 Rev 5

6.3

External synchronization

The STBB1 implements external synchronization pin. If and 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 in 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, this avoids unwanted current leakage

from the input to the load.

6.5

Protection features

The STBB1 implements different types of protection features.

6.5.1

Soft-start and short-circuit

After the EN pin is pulled high, or after a suitable voltage is applied to VIN, VINA and EN the

device initiates the startup phase. The average current limit is set to 400 mA at the

beginning and is gradually increased while tracking the output voltage increase. As soon the

output voltage reaches 1.0 V the average current limit is set to its nominal value.

This method allows for a current limit proportional to the output voltage. If there is a short in

This process is not handled by a timer so the device is also able to start up even with large

capacitive loads.

6.5.2

Under-voltage lockout

The under voltage lockout function prevents improper operation of STBB1 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.

6.5.3

Over-temperature 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.