ISL6334 Datasheet, PDF (14/30 Pages) Intersil Corporation – VR11.1, 4-Phase PWM Controller with Light Load Efficiency Enhancement and Load Current Monitoring

ISL6334, ISL6334A
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.
TABLE 1. PSI# OPERATION DECODING
PSI# FS SS
Non CI or (n-1) CI Drops to 1-phase
0
0
0
Non CI or (n-2) CI Drops to 2-phase
0
0
1
2-phase CI Drops to 1-phase
0
1
0
2-phase CI Drops to 2-phase
0
1
1
Normal CCM PWM Mode
1
x
x
The dropped PWM is forced low for 200ns (uncoupled case)
or until falling edge of coupled PWM (coupled case) then
pulled to VCC/2, while the remained PWM(s) sends out a
special 3-level PWM protocol that the dedicated VR11.1
drivers can decode and then enter diode emulation mode
with gate drive voltage optimization.
The ISL6334A only generates 2-level normal CCM PWM
except for faults. No dedicated VR11.1 driver is required.
See “Controller and Driver Recommendation” on page 3.
Switching Frequency
Switching frequency is determined by the selection of the
frequency-setting resistor, R_T, which is connected from FS
pin to GND or VCC. Equation 3 and Figure 3 are provided to
assist in selecting the correct resistor value.
R_T
=
2----.--5---X-----1---0----¹_---⁰_-
F_SW
(EQ. 3)
where F_SW is the switching frequency of each phase.
250
200
150
100
50
0
100k 200k 300k 400k 500k 600k 700k 800k 900k 1M
SWITCHING FREQUENCY (Hz)
FIGURE 3. SWITCHING FREQUENCY vs RT
Current Sensing
The ISL6334, ISL6334A senses current continuously for fast
response. The ISL6334, ISL6334A 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_L.
The sense current, I_SEN, is proportional to the inductor
current. The sensed current is used for current balance,
load-line regulation, and overcurrent protection.
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 13. The input bias current of the current sensing
amplifier is typically 60nA; less than 5kΩ input impedance is
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_L, flowing through the inductor, will also
pass through the DCR. Equation 4 shows the s-domain
equivalent voltage across the inductor V_L.
V_L(s) = I_L ⋅ (s ⋅ L + DCR)
(EQ. 4)
A simple R-C network across the inductor extracts the DCR
voltage, as shown in Figure 4.
V_IN
IL(s)
ISL6596
L
DCR
INDUCTOR
V_L
V_OUT
C_OUT
V_C(s)
PWM(n)
R
C
ISL6334, ISL6334A INTERNAL CIRCUIT
I_n
R_ISEN(n)
CURRENT
SENSE
ISEN-(n)
+
-
ISEN+(n)
C_T
I_SEN
=
I_L
---^D----^C-----^R-----
R_ISEN
FIGURE 4. DCR SENSING CONFIGURATION
14
FN6482.0
February 26, 2008