ISL6565ACR datasheet(16/28 Pages) INTERSIL

16 / 28 page

The ISL6565A, ISL6565B checks the VID inputs six times

every switching cycle. If the VID code is found to have

changed, the controller waits half of a complete cycle before

executing a 12.5mV change. If during the half-cycle wait

period, the difference between the DAC level and the new

VID code changes sign, no change is made. If the VID code

is more than 1 bit higher or lower than the DAC (not

recommended), the controller will execute 12.5mV changes

six times per cycle until VID and DAC are equal. It is

important to carefully control the rate of VID stepping in 1-bit

increments.

In order to ensure the smooth transition of output voltage

during VID change, a VID step change smoothing network is

required for an ISL6565A, ISL6565B based voltage

regulator. This network is composed of a 1k

Ω internal

resistor between the output of DAC and the capacitor CREF,

between the REF pin and ground. The selection of CREF is

based on the time duration for 1 bit VID change and the

allowable delay time.

Assuming the microprocessor controls the VID change at 1

bit every TVID, the relationship between CREF and TVID is

given by Equation 15.

As an example, for a VID step change rate of 5

µs per bit, the

value of CREF is 22nF based on Equation 15.

Temperature Compensation

MOSFET rDS(ON) and inductor DCR are both susceptible to

changes in value due to temperature. Since output voltage

positioning is derived from the channel current sensed

across these two elements, any variation in resistance

results in a corresponding error in the output voltage.

The temperature coefficient,

α, of the rDS(ON) or DCR is the

parameter that determines how much the resistance varies

with temperature. As temperature increases above ambient,

the average sensed current, IAVG, changes in proportion to

the temperature coefficient and temperature rise as shown in

Equation 16.

With this resulting error, IAVG can now be described as the

sum of two parts, the average sensed current at ambient

temperature and the resulting error current, IERR, due to the

temperature rise.

In order to compensate for this error current, the ISL6565A,

ISL6565B includes a temperature compensation circuit that

injects a current, ITCOMP, into the FB pin. This current is

created by pushing the average sense current through a

selectable external resistor, RTCOMP.

As shown in Figure 10, the voltage drop developed across

RTCOMP is then sensed and multiplied by a known gain,

KTC, which is determined by the internal IC temperature.

This gain creates the temperature compensation current,

ITCOMP, that is injected into the FB pin.

Select RTCOMP such that ITCOMP equals IERR over the

entire range of operating temperature. The resulting droop

current accurately represents the load current; achieving a

linear, temperature-independant load line.

Initialization

Prior to initialization, proper conditions must exist on the

enable inputs and VCC. When the conditions are met, the

controller begins soft-start. Once the output voltage is within

the proper window of operation, the controller asserts

PGOOD.

Enable and Disable

While in shutdown mode, the PWM outputs are held in a

high-impedance state to assure the drivers remain off. The

following input conditions must be met before the ISL6565A,

ISL6565B is released from shutdown mode.

1. The bias voltage applied at VCC must reach the internal

power-on reset (POR) rising threshold. Once this

threshold is reached, proper operation of all aspects of

the ISL6565A, ISL6565B is guaranteed. Hysteresis

between the rising and falling thresholds assure that once

enabled, the ISL6565A, ISL6565B will not inadvertently

turn off unless the bias voltage drops substantially (see

Electrical Specifications).

CREF

0.004X TVID

(EQ. 15)

IAVG

IAVG T

AMBIENT

()

α TT

AMBIENT

–

()

[]

⋅

(EQ. 16)

IERR T

()

IAVG T

AMBIENT

() α

TTAMBIENT

–

()

⋅⋅

(EQ. 17)

RFB

ISL6565A, ISL6565B

FIGURE 10. TEMPERATURE COMPENSATION CIRCUITRY

VDROOP

KTC

RTCOMP

TCOMP

IAVG

ITCOMP

VDIFF

IDROOP

ITCOMP

KTC T25

–

() I

AVG RTCOMP

⋅⋅

⋅

(EQ. 18)

ISL6565A, ISL6565B

ISL6565ACR Datasheet(PDF) 16 Page - Intersil Corporation

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