TS3552
2A/350kHz Synchronous Buck DC/DC Converter
4/11
Version: B11
Function Description
The TS3552 is a constant frequency current mode step-down synchronous DC/DC converter. It regulates input
voltage from 4.75V to 23V, down to an output voltage as low as 0.925V, and can provide 2A of continuous load
current.
Control Loop
During normal operation, the output voltage is sensed at FB pin through a resistive voltage divider and amplified
through the error amplifier. The voltage of error amplifier output pin – COMP is compared to the switch current to
controls the RS latch. At each cycle, the high side NMOS would be turned on when the oscillator sets the RS latch
and would be turned off when current comparator resets the RS latch. When the load current increases, the FB pin
voltage drops below 0.925V, it causes the COMP voltage increase until average inductor current arrive at new load
current.
Enable
The TS3552 EN pin provides digital control to turn on/turn off the regulator. When the voltage of EN exceeds the
threshold voltage, the regulator starts the soft start function. If the EN pin voltage is below than the threshold
voltage, only the bandgap voltage is alive. If the EN pin voltage is below than the shutdown threshold voltage, the
regulator will be disable and into the shutdown mode.
Maximum Load Current
The maximum load current decreases at lower input voltage because of large IR drop on the high side switch and
low side switch. The slope compensation signal reduces the peak inductor current as a function of the duty cycle to
prevent sub-harmonic oscillations at duty cycles greater than 50%.
Output Over Voltage Protection
When the FB pin voltage exceeds 20% of the regulation voltage, the output over voltage protection function will
discharge the COMP pin and the SS pin to GND, turning the high side MOSFET off.
Input Under Voltage Lockout
When the TS3552 power on, the internal circuits are held inactive until VIN exceeds the input UVLO threshold
voltage. And the regulator will be disabled when VIN below the input UVLO threshold voltage. The hysteretic of the
UVLO comparator is 400 mV.
Short Circuit Protection
The TS3552 provides short circuit protection function to prevent the device damage from short condition. When the
output short to ground, the oscillator frequency is reduced to prevent the inductor current increasing beyond the
current limit. In the meantime, the current limit is also reduced to lower the short current. Once the short condition is
removed, the frequency and current limit will return to normal.
Over Temperature Protection
The TS3552 incorporates an over temperature protection circuit to protect itself from overheating. When the
junction temperature exceeds the thermal shutdown threshold temperature, the regulator will be shutdown.
Compensation
The stability of the feedback circuit is controlled through COMP pin. The compensation value of the application
circuit is optimized for particular requirements. If different conversions are requires, some of the components may
need to be changes to ensure stability
.
