SP6120 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: Continued
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_CC Start Threshold vs. Temperature
2.750
-40
-15
10
35
60
85
Temperature (°C)
Figure 15. V_CC Stop Threshold vs. Temperature
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_OSC with V_CC = 5V
and CGH = CGL = Open.
THEORY OF OPERATIONS
General Overview
The SP6120 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 inter-
nal 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 lim-
ited by the external component selection. There-
fore, a secondary loop, including a window
comparator positioned 3% above and below the
reference, has been added to insure fast re-
sponse 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 commands from the main
and secondary loops, the Driver Logic is also
controlled by the Programming Logic, Fault
Logic and Zero Crossing Comparator. The Pro-
gramming Logic tells the Driver Logic whether
the controller is using a PFET or NFET high side
Date: 1/21/05
SP6120 Low Voltage, AnyFET^TM, Synchronous, Buck Controller
8
© Copyright 2005 Sipex Corporation