ISL6560 Datasheet, PDF (6/14 Pages) Intersil Corporation – Microprocessor CORE Voltage Regulator Two-Phase Buck PWM Controller

ISL6560
General Circuit Description
R_SENSE
INPUT
VOLTAGE
CS+
CS-
+Current _-
Comparator
ISL6560
OUTPUT
GATE
DRIVERS
and
Logic
RESET
SET
OSCILLATOR
GATE DRIVER
and
OUTPUT FETs
PWM1
GATE DRIVER
and
OUTPUT FETs
PWM2
CT
+
V_CORE
COMP
R_L
REF
gm ^-
Error
Amplifier
+
Reference
Voltage
FB
VID4
VID3
D/A
VID2
VID1
VID0
GND
FIGURE 1. FUNCTIONAL SYSTEM BLOCK DIAGRAM SHOWING MAJOR COMPONENTS
The ISL6560 is a two-power channel, current mode PWM
controller with input current sensing. A transconductance
error amplifier helps establish the desired droop voltage for
microprocessor power supplies and will be explained later.
Figure 1 is a functional system block diagram of the IC in a
power supply application. A single current sampling resistor,
R_SENSE, on the input side of the supply monitors the current
for both channels via a comparator within the ISL6560. A
single comparator insures that both channels are monitored
by the same circuitry, helping to balance the operating
current of each channel. During normal operation the
comparator is tripped by the peak inductor current,
terminating the conduction cycle. As more current is needed
to supply the output load, the comparator threshold voltage
is increased, increasing the inductor current to
accommodate the increased load demands.
by the amplifier attempting to make both inputs equal. This
does not happen because of the limited loop gain and
provides the bases for droop compensation mentioned
earlier and described below.
3.0
2.5
2.0
12.5V/V
1.5
1.0
{
0.5
Output
Disable
Threshold
0
0
20 40
60 80 100 120 140 160
V_CS(CL) (mV)
Circuit Operation
Figure 1 will be used to describes operation of the controller.
A transconductance error amplifier provides the major
voltage control function. The error amplifier’s positive input is
connected to an internal DAC that is programmed via a 5-bit
code from the microprocessor. Regulation is accomplished
FIGURE 2. CURRENT COMPARATOR THRESHOLD VOLTAGE
AS A FUNCTION OF VCOMP
Figure 2 shows a curve of the current comparator threshold
voltage as a function of the error amplifier output voltage,
V_COMP. From this curve, it can be seen that as V_COMP
6
FN9011.3