SP6128A Datasheet, PDF (4/10 Pages) Sipex Corporation – Low Voltage, Synchronous Step Down PWM Controller Ideal for 2A to 10A, Small Footprint, DC-DC Power Converters

FUNCTIONAL DIAGRAM
0.8V
Reference
1V _-
+
DRIVER ENABLE
FAULT
0.27V/ms
SOFTSTART
V_FB 10
COMP 6
GM
ERROR
+ ^AMP
-
-
350mV +
SHUTDOWN
5µA _{PWM COMP}
-
+
RESET
Dominant
R
Q
PWM
Logic
S
V_CC 3
ISET 11
UVLO
-
2.8V ON
2.7V OFF
+
GH
15µA
+
SWN
-
750mV RAMP
F = 300kHz
Over Current
SHUTDOWN
Reset
Dominant
S
FAULT
Q
R
2 PVCC
14 BST
Synchronous
Driver
13 GH
1 GL
12 SWN
4 PGND
5 GND
COMP
General Overview
The SP6128A is a constant frequency, voltage
mode, synchronous PWM controller designed
for low voltage, DC/DC step down converters.
It is intended to provide complete control for a
high power, high efficiency, precisely regulated
output voltage from a highly integrated 14-pin
solution.
The internal free-running oscillator accurately
sets the PWM frequency at 300kHz without
requiring any external elements and allows the
use of physically small, low value external com-
ponents without compromising performance. A
transconductance amplifier is used for the error
amplifier, which compares an attenuated sample
of the output voltage with a precision, 0.8V
reference voltage. The output of the error ampli-
fier (COMP), is compared to a 0.75V peak-to-
peak ramp waveform to provide PWM control.
The COMP pin provides access to the output of
the error amplifier and allows the use of external
components to stabilize the voltage loop.
OPERATION
High efficiency is obtained through the use of
synchronous rectification. Synchronous regula-
tors replace the catch diode in the standard buck
converter with a low R_DS(ON) N-channel
MOSFET switch allowing for significant ef-
ficiency improvements. The SP6128A in-
cludes two fast MOSFET drivers with inter-
nal non-overlap circuitry and drives a pair of
N-channel power transistors. The SP6128A
includes an internal 0.27V/ms soft-start cir-
cuit that provides controlled ramp up of the
output voltage, preventing overshoot and in-
rush current at power up.
Current limiting is implemented by monitoring
the voltage drop across the R_DS(ON) of the high
side N-channel MOSFET while it is conducting,
thereby eliminating the need for an external
sense resistor. The overcurrent threshold can be
programmed by a single resistor.
Rev. 05/25/04
SP6128A Low Voltage, Synchronous Step Down PWM Controller
4
© Copyright 2004 Sipex Corporation