SP6120B Datasheet, PDF (8/22 Pages) Sipex Corporation – Low Voltage, AnyFETTM, Synchronous ,Buck Controller Ideal for 2A to 10A, High Performance, DC-DC Power Converters

Typical Performance Characteristics
Unless otherwise specified: V_CC = BST = ENABLE = 3.3V, R_OSC = 18.7k, C_COMP = 0.1µF, C_SS = 0.1µF, CGH = CGL = 3.3nF, V_FB = 1.25V,
ISP = ISN = 1.25V, SWN = GND = PGND = 0V, T_AMB = 25°C.
2.900
2.850
2.875
2.825
2.850
2.800
2.825
2.775
2.800
-40
-15
10
35
60
85
Temperature (°C)
Figure 14. V Start Threshold vs. Temperature
CC
2.750
-40
-15
10
35
60
85
Temperature (°C)
Figure 15. V Stop Threshold vs. Temperature
CC
302
301
300
299
298
-40
-15
10
35
60
85
Temperature (°C)
Figure 16. Oscillator Frequency vs. Temperature
800
700
600
500
400
300
200
5
10
15
20
25
30
R_OSC (kΩ)
Figure 17. Oscillator Frequency vs. R with V = 5V
OSC
CC
and CGH = CGL = Open.
THEORY OF OPERATION
General Overview
The SP6120B is a constant frequency, voltage
mode PWM controller for low voltage, DC/DC
step down converters. It has a main loop where
an external resistor (R_OSC) sets the frequency and
the driver is controlled by the comparison of an
error amp output (COMP) and a 1V ramp signal.
The error amp has a transconductance of 600µS,
an output impedance of 3 MΩ, an internal pole at
2 MHz and a 1.25V reference input. Although
the main control loop is capable of 0% and 100%
duty cycle, its response time is limited by the
external component selection. Therefore, a sec-
ondary loop, including a window comparator
positioned 3% above and below the reference,
has been added to insure fast response to line and
load transients. A unique “Ripple & Frequency
Independent” algorithm, added to the secondary
loop, insures that the window comparator does
not interfere with the main loop during normal
operation. In addition to receiving driver com-
mands from the main and secondary loops, the
Driver Logic is also controlled by the Program-
ming Logic, Fault Logic and Zero Crossing
Comparator. The Programming Logic tells the
Driver Logic whether the controller is using a
PFET or NFET high side driver as well as whether
the controller is operating in continuous or dis-
continuous mode. The Fault Logic holds the high
and low side drivers off if V_CC dips below 2.75V,
if an over current condition exists, or if the part
is disabled through the ENABLE pin. The Zero
Crossing Comparator turns the lower driver off
Date: 5/25/04
SP6120B Low Voltage, AnyFET^TM, Synchronous, Buck Controller
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© Copyright 2004 Sipex Corporation