ISL6334DIRZ datasheet(12/28 Pages) INTERSIL

12 / 28 page

FN6802.2

August 31, 2010

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.

While the controller is operational (VCC above POR,

EN_VTT and EN_PWR are both high, valid VID inputs), it

can pull the PWM pins to ~40% of VCC (~2V for 5V VCC

bias) during various stages, such as soft-start delay, phase

shedding operation, or fault conditions (OC or OV events).

The matching driver's internal PWM resistor divider can

further raise the PWM potential, but not lower it below the

level set by the controller IC. Therefore, the controller's

PWM outputs are directly compatible with Intersil drivers that

require 5V PWM signal amplitudes. Drivers requiring 3.3V

PWM signal amplitudes are generally incompatible.

Switching Frequency

Switching frequency is determined by the selection of the

frequency-setting resistor, RT, 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.

where FSW is the switching frequency of each phase.

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, IL. The sense

current, ISEN, is proportional to the inductor current. The

sensed current is used for current balance 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 11. The input bias current of the current sensing

amplifier is typically 60nA; less than 5k

Ω 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 IL, flowing through the inductor, will also

pass through the DCR. Equation 4 shows the S-domain

equivalent voltage across the inductor VL.

TABLE 1. PSI# OPERATION DECODING

PSI#

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

(EQ. 3)

2.5X10

FSW

--------------------------

FIGURE 3. SWITCHING FREQUENCY vs RT

250

200

150

100

100k 200k 300k 400k 500k 600k 700k 800k 900k 1M

SWITCHING FREQUENCY (Hz)

VL s

()

IL sL DCR

⋅

()

⋅

(EQ. 4)

ISL6334D

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