TS3406

600mA / 1.5MHz Synchronous Buck Converter

4/7

Version: C12

Function Description (Continue)

Maximum Load Current

The TS3406 will operate with input supply voltage as low as 2.5V, however, the maximum load current decreases

at lower input due to large IR drop on the main switch and synchronous rectifier. 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%. Conversely the current limit increases as the duty cycle decreases.

Application Information

Setting the Output Voltage

Application circuit item shows the basic application circuit with TS3406 adjustable output version. The external

resistor sets the output voltage according to the following equation:

Inductor Selection

For most designs, the TS3406 operates with inductors of 1µH to 4.7µH. Low inductance values are physically

smaller but require faster switching, which results in some efficiency loss. The inductor value can be derived from

the following equation:

Where is inductor Ripple Current. Large value inductors lower ripple current and small value inductors result in high

ripple currents. Choose inductor ripple current approximately 35% of the maximum load current 600mA,

∆IL=210mA.

For output voltages above 2.0V, when light-load efficiency is important, the minimum recommended inductor is

2.2µH. For optimum voltage-positioning load transients, choose an inductor with DC series resistance in the 50mΩ

to 150mΩ range. For higher efficiency at heavy loads (above 200mA), or minimal load regulation (but some

transient overshoot), the resistance should be kept below 100mΩ. The DC current rating of the inductor should be

at least equal to the maximum load current plus half the ripple current to prevent core saturation (600mA+105mA).

Input Capacitor Selection

The input capacitor reduces the surge current drawn from the input and switching noise from the device. The input

capacitor impedance at the switching frequency shall be less than input source impedance to prevent high

frequency switching current passing to the input. A low ESR input capacitor sized for maximum RMS current must

be used. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and

small temperature coefficients. A 4.7µF ceramic capacitor for most applications is sufficient.

Table 1: Resistor Select for Output Voltage Setting

VOUT

R2

R1

1.2V

300K

300K

1.5V

300K

450K

1.8V

300K

600K

2.5V

300K

950K

Table 2: Inductor Select for Output Voltage Setting (Vcc-3.6V)

VOUT

1.2V

1.5V

1.8V

2.5V

Inductor

2.2uH

2.2uH

2.2uH

2.2uH

Part Number

WE-TPC

7440430027

7440430027

7440430027

7440430022

Note: Part Type MH or M (www.we-online.com)