TS3406_13 Datasheet, PDF (4/7 Pages) Taiwan Semiconductor Company, Ltd – 600mA / 1.5MHz Synchronous Buck Converter

TS3406
600mA / 1.5MHz Synchronous Buck Converter
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:
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
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:
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)
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.
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Version: C12