TS3406

600mA / 1.5MHz Synchronous Buck Converter

3/7

Version: A07

Block Diagram

Function Description

Operation

TS3406 is a monolithic switching mode Step-Down DC-DC converter. It utilizes internal MOSFETs to achieve high

efficiency and can generate very low output voltage by using internal reference at 0.6V. It operates at a fixed switching

frequency, and uses the slope compensated current mode architecture. This Step-Down DC-DC Converter supplies

600mA output current at VCC = 3V with input voltage range from 2.5V to 5.5V.

Current Mode PWM Control

Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for excellent

load and line responses and protection of the internal main switch (P-CH MOSFET) and synchronous rectifier (N-CH

MOSFET). During normal operation, the internal P-CH MOSFET is turned on for a certain time to ramp the inductor

current at each rising edge of the internal oscillator, and switched off when the peak inductor current is above the error

voltage. The current comparator, ICOMP, limits the peak inductor current. When the main switch is off, the

synchronous rectifier will be turned on immediately and stay on until either the inductor current starts to reverse, as

indicated by the current reversal comparator, IZERO, or the beginning of the next clock cycle. The OVDET comparator

controls output transient overshoots by turning the main switch off and keeping it off until the fault is no longer present.

Idle Mode Operation

At very light loads, the TS3406 automatically enters Idle Mode. In the Idle Mode, the inductor current may reach zero or

reverse on each pulse. The PWM control loop will automatically skip pulses to maintain output regulation. The bottom

MOSFET is turned off by the current reversal comparator, IZERO and the switch voltage will ring. This is discontinuous

mode operation, and is normal behavior for the switching regulator. When the input voltage decreases toward the value

of the output voltage, the TS3406 allows the main switch to remain on for more than one switching cycle and increases

the duty cycle until it reaches 100%. The output voltage then is the input voltage minus the voltage drop across the

main switch and the inductor. At low input supply voltage, the RDS(ON) of the P-CH MOSFET increases, and the

efficiency of the converter decreases. Caution must be exercised to ensure the heat dissipated not to exceed the

maximum junction temperature of the IC.