isl6334d Intersil Corporation, isl6334d Datasheet - Page 12

• Manufacturer Part Number: isl6334d
• Description: Vr11.1, 4-phase Pwm Controller With Phase Dropping, Droop Disabled And Load Current Monitoring Features
• Manufacturer: Intersil Corporation

When PSI# is asserted low, indicating the low power mode
operation of the processor, the controller drops the number of
active phases according to the logic on Table 1 for highlight
load efficiency performance. SS and FS pins are used to
program the controller in operation of non-coupled, 2-phase
coupled, or (n-x)-Phase coupled inductors. Different cases yield
different PWM output behaviors on both dropped phase(s) and
remained phase(s) as PSI# is asserted and de-asserted. A high
PSI# input signal pulls the controller back to normal CCM PWM
operation to sustain an immediate heavy transient load and
high efficiency. Note that “n-x” means n-x phase coupled and x
phase(s) are uncoupled.
Switching Frequency
Switching frequency is determined by the selection of the
frequency-setting resistor, R
pin to GND or VCC. Equation 3 and Figure 3 are provided to
assist in selecting the correct resistor value.
where F
Current Sensing
The ISL6334D senses current continuously for fast
response. The ISL6334D supports inductor DCR sensing, or
resistive sensing techniques. The associated channel
current sense amplifier uses the ISEN inputs to reproduce a
signal proportional to the inductor current, I
current, I
sensed current is used for current balance and overcurrent
protection.
R
Non CI or (n-1) CI Drops to 1-phase
Non CI or (n-2) CI Drops to 2-phase
2-phase CI Drops to 1-phase
2-phase CI Drops to 2-phase
Normal CCM PWM Mode
T
=
2.5X10
------------------------- -
250
200
150
100
50
SW
F
SEN
0
100k 200k 300k 400k 500k 600k 700k 800k 900k 1M
SW
FIGURE 3. SWITCHING FREQUENCY vs RT
TABLE 1. PSI# OPERATION DECODING
is the switching frequency of each phase.
10
, is proportional to the inductor current. The
SWITCHING FREQUENCY (Hz)
T
12
, which is connected from FS
PSI#
0
0
0
0
1
L
. The sense
FS
0
0
1
1
x
(EQ. 3)
SS
0
1
0
1
x
ISL6334D
The internal circuitry, shown in Figures 4 and 5, represents
one channel of an N-channel converter. This circuitry is
repeated for each channel in the converter, but may not be
active depending on the status of the PWM2, PWM3 and
PWM4 pins, as described in “PWM and PSI# Operation” on
page 11. The input bias current of the current sensing
amplifier is typically 60nA; less than 5k
preferred to minimized the offset error.
INDUCTOR DCR SENSING
An inductor’s winding is characteristic of a distributed
resistance, as measured by the DCR (Direct Current
Resistance) parameter. Consider the inductor DCR as a
separate lumped quantity, as shown in Figure 4. The
channel current I
pass through the DCR. Equation 4 shows the s-domain
equivalent voltage across the inductor V
A simple R-C network across the inductor extracts the DCR
voltage, as shown in Figure 4.
The voltage on the capacitor V
proportional to the channel current I
If the R-C network components are selected such that the
RC time constant (= R*C) matches the inductor time
constant (= L/DCR), the voltage across the capacitor V
equal to the voltage drop across the DCR, i.e., proportional
to the channel current.
V
ISL6334D INTERNAL CIRCUIT
V
C
L
s ( )
s ( )
CURRENT
=
SENSE
=
FIGURE 4. DCR SENSING CONFIGURATION
⎛
⎝
-------------------------------------------------------------------- -
I
I
s
L
n
I
SEN
⋅
⋅
-------------
DCR
(
ISL6596
s L
L
⋅
(
=
s RC
L
+
PWM(n)
+
⋅
, flowing through the inductor, will also
I
L
DCR
1
-------------------
R
⎞
⎠
DCR
ISEN
⋅
+
(
DCR I
)
1
+
-
)
V
IN
⋅
C
L
)
, can be shown to be
ISEN-(n)
ISEN+(n)
INDUCTOR
R
L
L
. See Equation 5.
I
L
Ω
V
s ( )
L
L
V
input impedance is
.
C
DCR
-
C
(s)
-
R
C
ISEN(n)
October 29, 2008
T
C
V
OUT
(EQ. 5)
OUT
(EQ. 4)
FN6802.0
C
is