Datasheet


SLUS489 − OCTOBER 2001
9
www.ti.com
APPLICATION INFORMATION
general information
The TPS43000 is a high-frequency, synchronous PWM controller optimized for distributed power, or
battery-powered applications where size and efficiency are of critical importance. It includes high-speed,
high-current MOSFET drivers for those applications requiring low R
DS(on)
external MOSFETs. (See functional
block diagram).
optimizing efficiency
The TPS43000 optimizes efficiency and extends battery life with its low quiescent current and its synchronous
rectifier topology. The additional features of low-power (LP) mode and PFM mode maintain high efficiency over
a wide range of load current.
modes of operation
The TPS43000 has four distinct modes of operation:
D fixed PWM with discontinuous conduction mode (DCM) possible
D fixed PWM with forced continuous conduction mode (CCM)
D automatic pulse frequency modulation (PFM) with DCM possible
D PFM with forced CCM
The device mode is controlled by the CCM and PFM
pins. The CCM pin lets the user decide whether to allow
DCM by connecting the pin to ground or to force CCM by connecting the pin to VIN. The PFM
pin lets the user
decide whether to allow automatic PFM by connecting the pin to ground or to force fixed PWM by connecting
the pin to VIN.
fixed PWM with DCM possible (PFM tied to VIN; CCM tied to ground)
In this mode, the device behaves like a standard switching regulator with the addition of a synchronous rectifier.
Shortly after the energizing MOSFET turns off, the synchronous rectifier turns on. The synchronous rectifier
turns off either when the inductor current goes discontinuous (DCM) or just prior to the start of the next clock
cycle (CCM) when the energizing MOSFET turns on. During the small time interval when neither the energizing
MOSFET nor the synchronous rectifier are turned on, the synchronous rectifier MOSFET body diode (or an
optional small external Schottky diode in parallel) carries the current to the output until it goes discontinuous.
The efficiency drops off at light loads as the losses become a larger percentage of the delivered load.