62381CHRTZ 查看數據表（PDF） - Renesas Electronics

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62381CHRTZ

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

Renesas Electronics 

ISL62381, ISL62382, ISL62383, ISL62381C, ISL62382C, ISL62383C

RTOP, RFB, CFB and CINT form the Type-II compensator. The

frequency domain transfer function is given by Equation 15:

GCOMPs = -s------R----1-T---O-+----P-s------C---R-I--N-T----TO-----P----1-+----+R----s-F----B--R-----F--C-B----F---CB-----F----B----

(EQ. 15)

CINT = 100pF

RFB

CFB

RTOP

- FB

VO

COMP

EA

+

RBOTTOM

REF

ISL6238

FIGURE 27. COMPENSATION REFERENCE CIRCUIT

The LC output filter has a double pole at its resonant frequency

that causes rapid phase change. The R3 modulator used in these

controllers make the LC output filter resemble a first order system

in which the closed loop stability can be achieved with the

recommended Type-II compensation network. Intersil provides a

PC-based tool (example page is shown later) that can be used

to calculate compensation network component values and help

simulate the loop frequency response.

LDO5 Linear Regulator

In addition to the two SMPS outputs, these controllers also

provide two linear regulator outputs. LDO5 is fixed 5V LDO output

capable of sourcing 100mA continuous current.

When the output of SMPS2 is programmed to 5V, SMPS2 will

automatically take over the load of LDO5. This provides a large

power savings and boosts the efficiency. After switchover to

SMPS2, the LDO5 output current plus the MOSFET drive

current should not exceed 100mA in order to guarantee the

LDO5 output voltage in the range of 5V ±5%. The total

MOSFET drive current can be estimated by Equation 16.

IDRIVE = Qg  FSW

(EQ. 16)

where Qg is the total gate charge of all the power MOSFET in

two SMPS regulators. Then the LDO5 output load current

should be less than 100mA-IDRIVE.

LDO3 Linear Regulator

ISL62381, ISL62381C, ISL62382 and ISL62382C include LDO3

linear regulator whose output is adjustable from 1.2V to 5V

through LDO3FB pin with a 1.2V reference voltage. It can be

independently enabled from both SMPS channels. Logic high of

LDO3EN will enable LDO3. LDO3 is capable of sourcing 100mA

continuous current and draws its power from LDO3IN pin, which

must be connected to a voltage greater than the LDO3 output

voltage plus the dropout voltage.

Currents in excess of the limit will cause the LDO3 voltage to

drop dramatically, limiting the power dissipation.

Thermal Monitor and Protection

LDO3 and LDO5 can dissipate non-trivial power inside these

controllers at high input-to-output voltage ratios and full load

conditions. To protect the silicon, these controllers continually

monitor the die temperature. If the temperature exceeds +150°C,

all outputs will be turned off to sharply curtail power dissipation.

The outputs will remain off until the junction temperature has

fallen below +135°C.

General Application Design Guide

This design guide is intended to provide a high-level explanation

of the steps necessary to design a single-phase power

converter. It is assumed that the reader is familiar with many of

the basic skills and techniques referenced in the following

section. In addition to this guide, Intersil provides complete

reference designs that include schematics, bills of materials, and

example board layouts.

Selecting the LC Output Filter

The duty cycle of an ideal buck converter is a function of the

input and the output voltage. This relationship is written as

Equation 17:

D = -V--V--O---I-U-N---T--

(EQ. 17)

The output inductor peak-to-peak ripple current is written as

Equation 18:

IPP = V-----O----U-F---T-S----W-----1---L-–-----D-----

(EQ. 18)

A typical step-down DC/DC converter will have an IP-P of 20%

to 40% of the maximum DC output load current. The value of

IP-P is selected based upon several criteria such as MOSFET

switching loss, inductor core loss, and the resistive loss of the

inductor winding. The DC copper loss of the inductor can be

estimated by Equation 19:

PCOPPER = ILOAD2  DCR

(EQ. 19)

Where ILOAD is the converter output DC current.

The copper loss can be significant so attention has to be given to

the DCR selection. Another factor to consider when choosing the

inductor is its saturation characteristics at elevated temperatures.

A saturated inductor could cause destruction of circuit

components, as well as nuisance OCP faults.

A DC/DC buck regulator must have output capacitance CO into

which ripple current IP-P can flow. Current IP-P develops out of

the capacitor. These two voltages are written as Equation 20:

VESR = IPP  ESR

(EQ. 20)

and Equation 21:

VC = 8-------C-----IO--P----P--F----S---W----

(EQ. 21)

If the output of the converter has to support a load with high

pulsating current, several capacitors will need to be paralleled to

reduce the total ESR until the required VP-P is achieved. The

FN6665 Rev 6.00

October 23, 2015

Page 18 of 24

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