SP6134HV Datasheet, PDF (7/14 Pages) Sipex Corporation – Dual Supply Synchronous Buck Controller

zero response is required, then compensation
can be a simple as an RC to ground. If a more
complex compensation is required, then the
amplifier has enough bandwidth (45° at 4 MHz)
and enough gain (60dB) to run Type III compen-
sation schemes with adequate gain and phase
margins at cross over frequencies greater than
50kHz.
The common mode output of the error amplifier
is 0.9V to 2.2V. Therefore, the PWM voltage
ramp has been set between 1.1V and 2.2V to
ensure proper 0% to 100% duty cycle capability.
The voltage loop also includes two other very
important features. One is an asynchronous start
up mode. Basically, the GL driver can not turn
on unless the GH driver has attempted to turn on
or the SS pin has exceeded 1.7V. This feature
prevents the controller from “dragging down”
the output voltage during startup or in fault
modes. The second feature is a 100% duty cycle
timeout that ensures synchronized refreshing of
the BST capacitor at very high duty ratios. In the
event that the GH driver is on for 20 continuous
clock cycles, a reset is given to the PWM flip
flop half way through the 21st cycle. This forces
GL to rise for the remainder of the cycle, in turn
refreshing the BST capacitor.
Gate Drivers
The SP6134H contains a pair of powerful 2Ω
SOURCE and 1.5Ω SINK drivers. These state
of the art drivers are designed to drive external
NFETs capable of handling up to 30A. Rise,
fall, and non-overlap times have all been minized
to achieve maximum efficiency. All drive pins
GH, GL & SWN are monitored continuously to
ensure that only one external NFET is ever on at
any given time.
THEORY OF OPERATION: Continued
GATE DRIVER TEST CONDITIONS
90%
GH(GL) _2V
10%
FALL TIME
GL(GH)
90%
2V
RISE TIME
10%
V(BST)
GH
Voltage
V(SWN)
V(VCC)
GL
Voltage
0V
V(VIN)
SWN
Voltage
-0V
-V(Diode) V
V(VIN)+V(VCC)
BST
Voltage
V(VCC)
NON-OVERLAP
TIME
Rev: C Date: 2/3/04
SP6134H Dual Supply, Synchronous Buck Controller
7
© Copyright 2004 Sipex Corporation