Datasheet

SLUU111 – June 2002
5
1-MHz, 3.3-V, High-Efficiency Synchronous Buck Converter With TPS43000 PWM Controller
+
Figure 1. TPS43000–001EVM Schematic
2 Design Procedure
2.1 Frequency Setting
The TPS43000 can operate either in constant frequency, or in an automatic PFM mode. In
the automatic PFM mode, the gate driver turns off when the inductor current goes
discontinuous, and turns on when the output voltage has fallen by 2%. This pulse skipping
can decrease gate-drive losses and significantly improve the efficiency at light load. (Refer
to the TPS43000 Data Sheet, TI Literature No. SLUS489 for more information.)The converter
is designed to operate at fixed 1 MHz above 0.2 A. The PFM mode is used when the load
decreases to below 0.2 A.
A resistor, R4, connected from the RT pin to ground, programs the oscillator frequency. The
approximate operating frequency is calculated in equation (1).
f (MHz) +
38
R4
(
kW
)
R4 = 37.4 kΩ is chosen for 1-MHz operation.
(1)