zl2005 Intersil Corporation, zl2005 Datasheet - Page 28

• Manufacturer Part Number: zl2005
• Description: Digital-dc? Integrated Power Management And Conversion Ic
• Manufacturer: Intersil Corporation

ZL2005
5.12 Efficiency Optimized Driver Dead-
time Control
The ZL2005 utilizes a closed loop algorithm to opti-
mize the dead-time applied between the gate drive sig-
nals for the top and bottom FETs. In a synchronous
buck converter, the MOSFET drive circuitry must be
designed such that the top and bottom MOSFETs are
never in the conducting state at the same time. (Poten-
tially damaging currents flow in the circuit if both top
and bottom MOSFETs are simultaneously on for peri-
ods of time exceeding a few nanoseconds.) Con-
versely, long periods of time in which both MOSFETs
are off reduce overall circuit efficiency by allowing
current to flow in their parasitic body diodes.
It is therefore advantageous to minimize this dead-
time to provide optimum circuit efficiency. In the first
order model of a buck converter, the duty cycle is
determined by the equation:
D = V
/V
--------------------
(29)
OUT
IN
However, non-idealities exist that cause the real duty
cycle to extend beyond the ideal. Deadtime is one of
those non-idealities that can be manipulated to
improve efficiency. The ZL2005 has an internal algo-
rithm that constantly adjusts deadtime non-overlap to
minimize duty cycle, thus maximizing efficiency. This
circuit will null out deadtime differences due to com-
ponent variation, temperature and loading effects.
This algorithm is independent of application circuit
parameters such as MOSFET type, gate driver delays,
rise and fall times and circuit layout. In addition, it
does not require drive or MOSFET voltage or current
waveform measurements.
28
FN6848.0
February 18, 2009