ISL62383 データシートの表示（PDF） - Renesas Electronics

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ISL62383

High-Efficiency, Quad or Triple-Output System Power Supply Controller for Notebook Computers

Renesas Electronics 

ISL62381, ISL62382, ISL62383, ISL62381C, ISL62382C, ISL62383C

automatically achieved by detecting the load current and

turning off LGATE when the inductor current reaches 0A.

Positive-going inductor current flows from either the source of

the high-side MOSFET, or the drain of the low-side MOSFET.

Negative-going inductor current flows into the drain of the low-

side MOSFET. When the low-side MOSFET conducts positive

inductor current, the phase voltage will be negative with

respect to the GND and PGND pins. Conversely, when the

low-side MOSFET conducts negative inductor current, the

phase voltage will be positive with respect to the GND and

PGND pins. These controllers monitor the phase voltage when

the low-side MOSFET is conducting inductor current to

determine its direction.

When the output load current is greater than or equal to ½ the

inductor ripple current, the inductor current is always positive,

and the converter is always in CCM. These controllers

minimize the conduction loss in this condition by forcing the

low-side MOSFET to operate as a synchronous rectifier.

When the output load current is less than ½ the inductor ripple

current, negative inductor current occurs. Sinking negative

inductor current through the low-side MOSFET lowers

efficiency through unnecessary conduction losses. These

controllers automatically enter DEM after the PHASE pin has

detected positive voltage and LGATE was allowed to go high

for eight consecutive PWM switching cycles. These controllers

will turn off the low-side MOSFET once the phase voltage turns

positive, indicating negative inductor current. These controllers

will return to CCM on the following cycle after the PHASE pin

detects negative voltage, indicating that the body diode of the

low-side MOSFET is conducting positive inductor current.

Efficiency can be further improved with a reduction of

unnecessary switching losses by reducing the PWM frequency.

It is characteristic of the R3 architecture for the PWM

frequency to decrease while in diode emulation. The extent of

the frequency reduction is proportional to the reduction of load

current. Upon entering DEM, the PWM frequency makes an

initial step-reduction because of a 33% step-increase of the

window voltage VW.

Because the switching frequency in DEM is a function of load

current, very light load conditions can produce frequencies well

into the audio band. This can be problematic if audible noise is

coupled into audio amplifier circuits. To prevent this from

occurring, these controllers allow the user to float the FCCM

input. This will allow DEM at light loads, but will prevent the

switching frequency from going below ~28kHz to prevent noise

injection into the audio band. A timer is reset each PWM pulse.

If the timer exceeds 30µs, LGATE is turned on, causing the

ramp voltage to reduce until another UGATE is commanded by

the voltage loop.

Overcurrent Protection

The overcurrent protection (OCP) setpoint is programmed with

resistor, ROCSET, that is connected across the OCSET and

PHASE pins.

PHASE1

ISL62381

DCR

L

IL

+

VDCR

_

ROCSET

CSEN

10µA

OCSET1

+ VROCSET _

RO

ISEN1

VO

CO

FIGURE 26. OVERCURRENT-SET CIRCUIT

Figure 26 shows the overcurrent-set circuit for SMPS1. The

inductor consists of inductance L and the DC resistance

(DCR). The inductor DC current IL creates a voltage drop

across DCR, given by Equation 6:

VDCR = IL  DCR

(EQ. 6)

Theses controllers sink a 10µA current into the OCSET1 pin,

creating a DC voltage drop across the resistor ROCSET, given

by Equation 7:

VROCSET = 10A  ROCSET

(EQ. 7)

Resistor RO is connected between the ISEN1 pin and the

actual output of the converter. During normal operation, the

ISEN1 pin is a high impedance path, therefore there is no

voltage drop across RO. The DC voltage difference between

the OCSET1 pin and the ISEN1 pin can be established using

Equation 8:

VOCSET1–VISEN1 = IL  DCR – 10A  ROCSET

(EQ. 8)

These controllers monitor the OCSET1 pin and the ISEN1 pin

voltages. Once the OCSET1 pin voltage is higher than the

ISEN1 pin voltage for more than 10µs, these controllers declare

an OCP fault. The value of ROCSET is then written as

Equation 9:

ROCSET = -I-O-----1C---0----D----A-C-----R---

(EQ. 9)

Where:

- ROCSET () is the resistor used to program the

overcurrent setpoint

- IOC is the output current threshold that will activate the

OCP circuit

- DCR is the inductor DC resistance

For example, if IOC is 20A and DCR is 4.5m, the choice of

ROCSET is ROCSET = 20A x 4.5m/10µA = 9k

FN6665 Rev 6.00

October 23, 2015

Page 16 of 24

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