Datasheet LX1663ACN, LX1663ACD, LX1662CN, LX1662CD, LX1662ACN Datasheet (Microsemi Corporation)

LIN DOC #: 1662

SS

TDRV

V

CC

INV
V

CC_CORE

VID0
VID1
VID2
VID3

VID4

C

T

BDRV

GND

V

C1

U1

LX1662

VID3

C

5

1µF

12V

R

1

V

OUT

5V

14-pin, Narrow Body SOIC

Q

1

IRL3102

L

1

, 2.5µH

6.3V, 1500µF x 3**

14

13

12

11

10

9

1

2

3

4

5

6

7

8

C

8

680pF

VID2

VID1

VID0

VID4

C

3

0.1µF

2.5m9

Supply Voltage
for CPU Core

6.3V
1500µF x3

** Three capacitors for Pentium

Four capacitors for Pentium II

Q

2

IRL3303

C

1

C

2

L

2

1µH

LX1662/62A, LX1663/63A

S

INGLE-CHIP PROGRAMMABLE

PWM C

ONTROLLERS WITH

5-BIT DAC

T HE I NFINITE P OWER OF I NNOVATION

DESCRIPTION KEY FEATURES

The LX1662/62A and LX1663/63A are
Monolithic Switching Regulator Con­troller IC’s designed to provide a low cost,

high performance adjustable power supply
for advanced microprocessors and other
applications requiring a very fast transient
response and a high degree of accuracy.

Short-Circuit Current Limiting with-

out Expensive Current Sense Resistors.

Current-sensing mechanism can use PCB
trace resistance or the parasitic resistance of
the main inductor. The LX1662A and
LX1663A have reduced current sense com­parator threshold for optimum perfor­mance using a PCB trace. For applications
requiring a high degree of accuracy, a
conventional sense resistor can be used to
sense current.

Programmable Synchronous Recti-

fier Driver for CPU Core. The main

output is adjustable from 1.3V to 3.5V using
a 5-bit code. The IC can read a VID signal
set by a DIP switch on the motherboard, or
hardwired into the processor’s package (as
in the case of Pentium

®

Pro and Pentium II
processors). The 5-bit code adjusts the
output voltage between 1.30 and 2.05V in
50mV increments and between 2.0 and 3.5V
in 100mV increments, conforming to the

IMPORTANT: For the most current data, consult LinFinity's web site: http://www.linfinity.com.

Intel Corporation specification. The device
can drive dual MOSFET’s resulting in typical
efficiencies of 85 - 90% even with loads in
excess of 10 amperes. For cost sensitive
applications, the bottom MOSFET can be
replaced with a Schottky diode (non-syn­chronous operation).

Smallest Package Size. The LX1662 is

available in a narrow body 14-pin surface
mount IC package for space sensitive appli­cations. The LX1663 provides the additional
functions of Over Voltage Protection (OVP)
and Power Good (PWRGD) output drives
for applications requiring output voltage
monitoring and protection functions.

Ultra-Fast Transient Response Re-

duces System Cost. The modulated off-

time architecture results in the fastest tran­sient response for a given inductor, reduc­ing output capacitor requirements, and re­ducing the total regulator system cost.

Over-Voltage Protection and Power

Good Flag. The OVP output in the LX1663

& LX1663A can be used to drive an SCR
crowbar circuit to protect the load in the
event of a short-circuit of the main MOSFET.
The LX1663 & LX1663A also have a logic­level Power Good Flag to signal when the
output voltage is out of specified limits.

P RODUCTION DATA SHEET

■ 5-bit Programmable Output For CPU Core
Supply

■ No Sense Resistor Required For Short­Circuit Current Limiting

■ Designed To Drive Either Synchronous Or
Non-Synchronous Output Stages

■ Lowest System Cost Possible For Price­Sensitive Pentium And Pentium II Class
Applications

■ Soft-Start Capability

■ Modulated, Constant Off-Time Architecture

For Fast Transient Response And Simple
System Design

■ Available Over-Voltage Protection (OVP)
Crowbar Driver And Power Good Flag
(LX1663 only)

■ Small, Surface-Mount Packages

APPLICATIONS

■ Socket 7 Microprocessor Supplies
(including Intel Pentium Processor, AMD-

TM

K6

And Cyrix® 6x86TM, Gx86TM and M2

Processors)

■ Pentium II and Deschutes Processor & L2­Cache Supplies

■ Voltage Regulator Modules

■ General Purpose DC:DC Converter

Applications

TM

LX1662

IN A PENTIUM/PENTIUM II

SINGLE-CHIP POWER

SUPPLY SOLUTION

T

(°C)

A

0 to 70

Note: All surface-mount packages are available in Tape & Reel. Append the letter "T" to part number. (i.e. LX1662CDT)

Copyright © 1999
Rev. 1.1 11/99

PRODUCT HIGHLIGHT

PACKAGE ORDER INFORMATION

11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: [phone]

N

Plastic DIP
14-pin

LX1662CN LX1663CN LX1662CD LX1663CD

LX1662ACN LX1663ACN LX1662ACD LX1663ACD

L INF INITY MICROELECTRONICS INC.

Plastic DIP

N

16-pin

Plastic SOIC

D

14-pin

Plastic SOIC

D

16-pin

for

See next page

Selection Guide

1

PRODUCT DATABOOK 1996/1997

LX1662/62A, LX1663/63A

S

INGLE-CHIP PROGRAMMABLE

P RODUCTION DATA SHEET

PWM C

ONTROLLERS WITH

5-BIT DAC

DEVICE SELECTION GUIDE

OVP and Current-Sense

DEVICE Packages Power Good Comp. Thresh. (mV) Optimal Load

LX1662 14-pin SOIC
LX1662A & DIP 60 Pentium II (> 10A)
LX1663 16-pin SOIC
LX1663A & DIP 60 Pentium II (> 10A)

No

Yes

100 Pentium-class (<10A)

100 Pentium-class (<10A)

ABSOLUTE MAXIMUM RATINGS (Note 1)

Supply Voltage (VC1) .................................................................................................... 25V

Supply Voltage (VCC) .................................................................................................... 15V

Output Drive Peak Current Source (500ns)............................................................... 1.5A

Output Drive Peak Current Sink (500ns) ................................................................... 1.5A

Input Voltage (SS, INV, V
Operating Junction Temperature

, CT, VID0-VID4) ........................................... -0.3V to 6V

CC_CORE

Plastic (N & D Packages) ...................................................................................... 150°C

Storage Temperature Range .................................................................... -65°C to +150°C

Lead Temperature (Soldering, 10 Seconds) ............................................................. 300°C

Note 1. Exceeding these ratings could cause damage to the device. All voltages are with respect

to Ground. Currents are positive into, negative out of the specified terminal. Pin
numbers refer to DIL packages only.

THERMAL DATA

N PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

D PACKAGE:

THERMAL RESISTANCE-JUNCTION TO AMBIENT,

Junction Temperature Calculation: TJ = TA + (PD x θJA).
The θJA numbers are guidelines for the thermal performance of the device/pc-board system.
All of the above assume no ambient airflow

θθ

θ

θθ

JA

θθ

θ

θθ

JA

65°C/W

120°C/W

PACKAGE PIN OUTS

1 14

SS

213

INV

312

V

CC_CORE

411

VID0

510

VID1

69

VID2
VID3

78

N PACKAGE — 14-Pin

LX1662/1662A (Top View)

1 16

SS

215

INV

314

V

CC_CORE

413

VID0

512

VID1

611

VID2

710

VID3

89

VID4

N PACKAGE — 16-Pin

LX1663/1663A (Top View)

1 14

SS

213

INV

V

CC_CORE

VID0
VID1
VID2
VID3

312

411

510

69

78

D PACKAGE — 14-Pin

LX1662/1662A (Top View)

1 16

SS

215

INV

V

CC_CORE

VID0
VID1
VID2
VID3
VID4

314

413

512

611

710

89

D PACKAGE — 16-Pin

LX1663/1663A (Top View)

V

C1

TDRV
GND
BDRV
V

CC

C

T

VID4

V

C1

TDRV
GND
BDRV
V

CC

C

T

OV
PWRGD

V

C1

TDRV
GND
BDRV
V

CC

C

T

VID4

V

C1

TDRV
GND
BDRV
V

CC

C

T

OV
PWRGD

2

Copyright © 1999

Rev. 1.1 11/99

PRODUCT DATABOOK 1996/1997

LX1662/62A, LX1663/63A

S

INGLE-CHIP PROGRAMMABLE

P RODUCTION DATA SHEET

ELECTRICAL CHARACTERISTICS

(

Unless otherwise specified, 10.8 < VCC < 13.2, 0°C ≤ TA ≤ 70°C. Test conditions: VCC = 12V, T = 25°C. Use Application Circuit.

Parameter

Reference & DAC Section (See Table 1 - Next Page)

Regulation Accuracy (See Table 1) (Less 40mV output adaptive positioning), VCC = 12V, I
Regulation Accuracy 1.8V ≤ V

Timing Section

Off Time Initial OT V

Off Time Temp Stability V
Discharging Current I
Ramp Peak V
Ramp Peak-Valley V

Ramp Valley Delay to Output 10% Overdrive

Error Comparator Section

Input Bias Current I
Input Offset Voltage V
EC Delay to Output 10% Overdrive

Current Sense Section

Input Bias Current (V
Pulse By Pulse C

L

CS Delay to Output 10% Overdrive

Pin) I

CC_CORE

LX1662/1663 V
LX1662A/1663A Initial Accuracy

Output Drivers Section

Drive Rise Time TRVC1 = VCC = 12V, CL = 3000pF
Drive Fall Time TFVC1 = VCC = 12V, CL = 3000pF
Drive High V

Drive Low V

Output Pull Down V

UVLO and S.S. Section

Start-Up Threshold V
Hysteresis V
SS Sink Current I
SS Sat Voltage V

Supply Current Section

Dynamic Operating Current I

Power Good / Over-Voltage Protection Section (LX1663 Only)

Lower Threshold (V
Hysteresis
Power Good Voltage Low I
Over-Voltage Threshold (V
OVP Sourcing Current VOV = 5V

Symbol

DISVCC_CORE

P

RPPVCC_CORE

B

IO

B

CLP

DHVCC

DLVCC

PDVCC

ST

HYST

SD

OLVC1

CD

= 1.3V, CT = 390pF

CC_CORE

V

= 3.5V, CT = 390pF

CC_CORE

= 1.3V to 3.5V

CC_CORE

= 1.3V, VCT = 1.5V

= 1.3V

V

= 3.5V

CC_CORE

1.3V < VSS = V

1.3V < V
Initial Accuracy

= VCC = 12V, I

VCC = VCC = 12V, I

= VCC = 12V, I

VCC = VCC = 12V, I

= VC = 0, I

VC1 = 10.1V

= 9V, ISD = 200µA

VCC = VC1 = 12V, Out Freq = 200kHz, CL = 0

/ DAC

CC_CORE

= 5mA

PWRGD

/ V

CC_CORE

PWM C

Test Conditions

≤ 2.8V

OUT

< 3.5V

INV

= V

INV

CC_CORE

SOURCE

SINK

SOURCE

SINK

PULL UP

)

OUT

)

DAC

< 3.5V

= 20mA

= 200mA

= 20mA

= 200mA

= 2mA

ONTROLLERS WITH

5-BIT DAC

= 6A

LOAD

LX1662/1663 (A)

Min. Typ. Max.

-30 30 mV

-1 1 %

180 210 240 µA

0.9 1 1.1 V

0.37 0.42 0.47 V

36 41 46 mV

85 100 115 mV
50 60 70 mV

9.9 10.1 10.4 V

2 5.5 mA

88 90 92 %

110 117 125 %

30 45 mA

)

Units

2µs
1µs

40 ppm

2V

100 ns

0.8 2 µA

200 ns

27 35 µA

200 ns

70 ns
70 ns
11 V
10 V

0.06 0.1 V

0.8 1.2 V

0.8 1.4 V

0.31 V

0.15 0.6 V

27 mA

1%

0.5 0.7 V

Copyright © 1999
Rev. 1.1 11/99

3

PRODUCT DATABOOK 1996/1997

0A

5A/Div.

Time - 100µs/Div.

2.8V
100mV/Div.

Output Load

0 to 14A

Output Voltage

LX1662/62A, LX1663/63A

S

INGLE-CHIP PROGRAMMABLE

P RODUCTION DATA SHEET

ELECTRICAL CHARACTERISTICS

Table 1 - Adaptive Transient Voltage Output (Output Voltage Setpoint  Typical)

Processor Pins

0 = Ground, 1 = Open (Floating)

VID4 VID3 VID2 VID1 VID0

01111 1.34V 1.30V
01110 1.39V 1.35V
01101 1.44V 1.40V
01100 1.49V 1.45V
01011 1.54V 1.50V
01010 1.59V 1.55V
01001 1.64V 1.60V
01000 1.69V 1.65V
00111 1.74V 1.70V
00110 1.79V 1.75V
00101 1.84V 1.80V
00100 1.89V 1.85V
00011 1.94V 1.90V
00010 1.99V 1.95V
00001 2.04V 2.00V
00000 2.09V 2.05V
11111 2.04V 2.00V
11110 2.14V 2.10V
11101 2.24V 2.20V
11100 2.34V 2.30V
11011 2.44V 2.40V
11010 2.54V 2.50V
11001 2.64V 2.60V
11000 2.74V 2.70V
10111 2.84V 2.80V
10110 2.94V 2.90V
10101 3.04V 3.00V
10100 3.14V 3.10V
10011 3.24V 3.20V
10010 3.34V 3.30V
10001 3.44V 3.40V
10000 3.54V 3.50V

* Nominal = DAC setpoint voltage with no adaptive output voltage positioning.

PWM C

ONTROLLERS WITH

5-BIT DAC

Output Voltage (V

0.0A Nominal Output*

CC_CORE

)

Note:

Adaptive Transient Voltage Output

In order to improve transient response a
40mV offset is built into the Current Sense
comparator. At high currents, the peak
output voltage will be lower than the
nominal set point , as shown in Figure 1.
The actual output voltage will be a function
of the sense resistor, output current and
output ripple.

4

FIGURE 1 — Output Transient Response

(Using 5mΩ sense resistor and 5µH output inductor)

Copyright © 1999

Rev. 1.1 11/99

PRODUCT DATABOOK 1996/1997

LX1662/62A, LX1663/63A

S

INGLE-CHIP PROGRAMMABLE

P RODUCTION DATA SHEET

CHARACTERISTICS CURVES

PWM C

ONTROLLERS WITH

5-BIT DAC

95

90

85

EFFICIENCY (%)__

80

Output Set Point

EFFICIENCY AT 3.1V

75

70

1234567891011121314

EFFICIENCY AT 2.8V
EFFICIENCY AT 1.8V

I

OUT

(A)

FIGURE 2 — Efficiency Test Results:

Non-Synchronous Operation, VIN = 5V

90

100

95

90

85

EFFICIENCY (%)__

80

75

70

Output Set Point

EFFICIENCY AT 3.1V
EFFICIENCY AT 2.8V

EFFICIENCY AT 1.8V

1234567891011121314

I

(A)

OUT

FIGURE 3 — Efficiency Test Results:

Synchronous Operation, VIN = 5V

85

80

75

70

Output Se t Point

1.8V EFF ICIENCY

65

60

1234567891011121314

2.8V EFF ICIENCY

3.3V EFF ICIENCY

I

(A)

OUT

FIGURE 4 — Efficiency Test Results: Synchronous Operation, VIN = 12V.

Note: Non-synchronous operation not recommended for 12V operation, due to power loss in Schottky diode.

Copyright © 1999
Rev. 1.1 11/99

5

PRODUCT DATABOOK 1996/1997

V

LX1662/62A, LX1663/63A

S

INGLE-CHIP PROGRAMMABLE

P RODUCTION DATA SHEET

BLOCK DIAGRAM

V

1

SS

CC

2V Out

UVLO

10.6/10.1

PWM C

Trimmed

2V REF

Internal

V

CC

ONTROLLERS WITH

V

REG

5-BIT DAC

PWM Latch

S

R DOM

RQ

V

16

C1

Q

TDRV

15

GND

14

INV

CC_CORE

40mV

2

100mV

3

11

C

T

**

VID0 VID16VID27VID38VID4

Error Comp

CS Comp

10k

D OUT

DAC

4 5

OV

Off-Time

Controller

Note: Pin numbers are correct for LX1663/1663A, 16-pin package.

Break

Before

Make

SYNC EN

0.7V

Comp

OV Comp

UV Comp

LX1663/1663A ONLY

* Not connected on the LX1662/1662A.

** 60mV in LX1662A & LX1663A

13

12

10

9

BDRV

V

CC

OV*

PWRGD*

FIGURE 5 — Block Diagram

6

Copyright © 1999

Rev. 1.1 11/99

PRODUCT DATABOOK 1996/1997

S

INGLE-CHIP PROGRAMMABLE

P RODUCTION DATA SHEET

FUNCTIONAL PIN DESCRIPTION

Pin LX1662 LX1663

Name Pin # Pin # Description

PWM C

LX1662/62A, LX1663/63A

ONTROLLERS WITH

5-BIT DAC

SS 1 1

INV 2 2

V

CC_CORE

VID0 4 4

VID1 5 5

VID2 6 6

VID3 7 7

VID4 8 8

PWRGD N.C. 9

OV N.C. 10

C

T

V

CC

BDRV 11 13

GND 12 14

TDRV 13 15

V

C1

33

911

10 12

14 16

Soft-Start pin, internally connected to the non-inverting input of the error comparator.

Inverting input of the error comparator.

Output voltage. Connected to non-inverting input of the current-sense comparator.

Voltage Identification pin (LSB) input used to set output voltage.

Voltage Identification pin (2nd SB) input.

Voltage Identification pin (3rd SB) input.

Voltage Identification pin (4th SB) input.

Voltage Identification pin (MSB) input. This pin is also the range select pin — when low
(CLOSED), output voltage is set to between 1.30 and 2.05V in 0.05V increments. When high
(OPEN), output is adjusted from 2.0 to 3.5V in 0.1V increments.

Open collector output pulls low when the output voltage is out of limits.

SCR driver goes high when the processor's supply is over specified voltage limits.

The off-time is programmed by connecting a timing capacitor to this pin.

This is the (12V) supply to the IC, as well as gate drive to the bottom FET.

This is the gate drive to the bottom FET. Leave open in non-synchronous operation (when bottom
FET is replaced by a Schottky diode).

Both power and signal ground of the device.

Gate drive for top MOSFET.

This pin is a separate power supply input for the top drive. Can be connected to a charge pump
when only 12V is available.

Copyright © 1999
Rev. 1.1 11/99

7

PRODUCT DATABOOK 1996/1997

LX1662/62A, LX1663/63A

S

INGLE-CHIP PROGRAMMABLE

P RODUCTION DATA SHEET

THEORY OF OPERATION

PWM C

ONTROLLERS WITH

5-BIT DAC

IC OPERATION

Referring to the block diagram and typical application circuit, the
output turns ON the top MOSFET, allowing the inductor current
to increase. At the error comparator threshold, the PWM latch is
reset, the top MOSFET turns OFF and the synchronous MOSFET
turns ON. The OFF-time capacitor C
At the valley voltage, the synchronous MOSFET turns OFF and the
top MOSFET turns on. A special break-before-make circuit
prevents simultaneous conduction of the two MOSFETs.

The V
response. The INV pin is connected to the positive side of the
current sense resistor, so the controller regulates the positive side
of the sense resistor. At light loads, the output voltage will be
regulated above the nominal setpoint voltage. At heavy loads, the
output voltage will drop below the nominal setpoint voltage. To
minimize frequency variation with varying output voltage, the
OFF-time is modulated as a function of the voltage at the V
pin.

ERROR VOLTAGE COMPARATOR

The error voltage comparator compares the voltage at the positive
side of the sense resistor to the set voltage plus 40mV. An external
filter is recommended for high-frequency noise.

CURRENT LIMIT

Current limiting is done by sensing the inductor current. Exceed­ing the current sense threshold turns the output drive OFF and
latches it OFF until the PWM latch Set input goes high again. See
Current Limit Section in "Using The LX1662/63 Devices" later in
this data sheet.

OFF-TIME CONTROL TIMING SECTION

The timing capacitor C
timing capacitor is quickly charged during the ON time of the top
MOSFET and allowed to discharge when the top MOSFET is OFF.
In order to minimize frequency variations while providing differ­ent supply voltages, the discharge current is modulated by the
voltage at the V
to the V

UNDER VOLTAGE LOCKOUT SECTION

The purpose of the UVLO is to keep the output drive off until the
input voltage reaches the start-up threshold. At voltages below
the start-up voltage, the UVLO comparator disables the internal
biasing, and turns off the output drives, and the SS (Soft-Start) pin
is pulled low.

CC_CORE

CC_CORE

pin is offset by +40mV to enhance transient

allows programming of the OFF-time. The

T

pin. The OFF-time is inversely proportional

CC_CORE

voltage.

is now allowed to discharge.

T

CC_CORE

SYNCHRONOUS CONTROL SECTION

The synchronous control section incorporates a unique break­before-make function to ensure that the primary switch and the
synchronous switch are not turned on at the same time. Approxi­mately 100 nanoseconds of deadtime is provided by the break­before-make circuitry to protect the MOSFET switches.

PROGRAMMING THE OUTPUT VOLTAGE

The output voltage is set by means of a 5-bit digital Voltage
Identification (VID) word (See Table 1). The VID code may be
incorporated into the package of the processor or the output
voltage can be set by means of a DIP switch or jumpers. For a low
or '0' signal, connect the VID pin to ground (DIP switch ON/
CLOSED); for a high or '1' signal, leave the VID pin open (DIP
switch OFF/OPEN).

The five VID pins on the LX166x series are designed to
interface directly with a Pentium Pro or Pentium II processor.
Therefore, all inputs are expected to be either ground or floating.
Any floating input will be pulled high by internal connections. If
using a Socket 7 processor, or other load, the VID code can be set
directly by connecting jumpers or DIP switches to the VID[0:4]
pins.

The VID pins are not designed to take TTL inputs, and
should not be connected high. Unpredictable output voltages
may result. If the LX166x devices are to be connected to a logic
circuit, such as BIOS, for programming of output voltage, they
should be buffered using a CMOS gate with open-drain, such as
a 74HC125 or 74C906.

POWER GOOD SIGNAL (LX1663 only)

An open collector output is provided which presents high
impedance when the output voltage is between 90% and 117% of
the programmed VID voltage, measured at the SS pin. Outside this
window the output presents a low impedance path to ground.
The Power Good function also toggles low during OVP operation.

OVER-VOLTAGE PROTECTION

The controller is inherently protected from an over-voltage
condition due to its constant OFF-time architecture. However,
should a failure occur at the power switch, an over-voltage drive
pin is provided (on the LX1663 only) which can drive an external
SCR crowbar (Q
must be removed and power recycled for the LX1663 to resume
normal operation (See Figure 9).

), and so blow a fuse (F1). The fault condition

3

8

Copyright © 1999

Rev. 1.1 11/99

PRODUCT DATABOOK 1996/1997

T

e

LX1662/62A, LX1663/63A

S

INGLE-CHIP PROGRAMMABLE

P RODUCTION DATA SHEET

APPLICATION INFORMATION

PWM C

ONTROLLERS WITH

5-BIT DAC

VID0
VID1
VID2
VID3
VID4

C

0.1µF

12V

3

1

2

3

4

5

6

7

SS
INV
V

CC_CORE

VID0
VID1
VID2
VID3

U1

LX1662

V

TDRV

GND

BDRV

V

VID4

14

C1

13

12

11

10

CC

9

C

T

8

C

5

1µF

C

8

680pF

1µH

L

2

5V

1500µF x3

Q
IRL3102

Q
IRL3303

6.3V

C

2

1

2

6.3V, 1500µF x 3**

R

S

C

, 2.5µH

L

1

** Three capacitors for Pentium

14-pin, Narrow Body SOIC

Four capacitors for Pentium II

FIGURE 6 — LX1662 In A Pentium / Pentium II Processor Single Chip Power Supply Controller

Solution With Loss-Less Current Sensing (Synchronous)

S

V

Supply Voltage

OU

for CPU Core

C

1

VID0
VID1
VID2
VID3
VID4

C

0.1µF

12V

3

U1

LX1662

1

SS

2

INV

3

V

CC_CORE

4

VID0

5

VID1

6

VID2

7

VID3 VID4

V
TDRV
GND

BDRV

V

14

C1

13

12

11

10

CC

9

C

T

8

C

5

1µF

MBR2535

C

8

680pF

D

1

5V

6.3V
1500µF x3

C

2

Q

1

IRL3102

L

, 5µH

1

6.3V, 1500µF x 3**

** Three capacitors for Pentium

Four capacitors for Pentium II

R

0.005

14-pin, Narrow Body SOIC

FIGURE 7 — LX1662 In A Non-Synchronous Pentium / Socket 7 Power Supply Application

1

V

OUT

Supply Voltag
for CPU Core

C

1

Copyright © 1999
Rev. 1.1 11/99

9

PRODUCT DATABOOK 1996/1997

LX1662/62A, LX1663/63A

S

INGLE-CHIP PROGRAMMABLE

P RODUCTION DATA SHEET

APPLICATION INFORMATION

PWM C

12V

ONTROLLERS WITH

F

1

20A

5-BIT DAC

5V

6.3V

VID0
VID1
VID2
VID3
VID4

C

0.1µF

3

U1

C
1µF

5

LX1663

1

SS

2

INV

3

V

CC_CORE

4

VID0

5

VID1

6

VID2

7

VID3

89

VID4 PWRGD

16-pin

Narrow Body SOIC

V

TDRV

GND

BDRV

V

OV

16

C1

15

14

13

12

CC

11

C

T

10

IRL3102

C

8

680pF

Q

1

OV
PWRGD

1500µF x3

C

2

R

S

Q

2

IRL3303

6.3V, 1500µF x 3**

** Three capacitors for Pentium

Four capacitors for Pentium II

C

, 2.5µH

L

1

S

Supply Voltage
for CPU Core

C

FIGURE 8 — Pentium II Processor Application With OVP, Power Good And Loss-Less Current Sensing (Synchronous)

Q

1

PWRGD

F1 20A

16V
1500µF x3

, 2.5µH

L

1

Q

2

IRL3303

C

2

12V

2.5m9

Q
SCR
2N6504

R

1

3

VID0
VID1
VID2
VID3
VID4

C

0.1µF

D

3

1N4148

C

9

3

1µF

U1

LX1663

1

SS

2

INV

3

V

CC_CORE

4

VID0

5

VID1

6

VID2

7

VID3

89

VID4 PWRGD

V
TDRV
GND

BDRV

V

OV

C1

CC

C

T

16

15

14

13

12

C8, 1200pF

11

10

C10, 1µF

C

0.1µF

R

7

10

10

D

2

1N4148

D

R
10k

IRL3102

4

1N5817

2

16-pin

Narrow Body SOIC

V

OUT

1

Supply Voltage

V

for CPU Core

C

1

6.3V, 1500µF x 3**

** Three capacitors for Pentium
Four capacitors for Pentium II

OUT

10

FIGURE 9 — Full-Featured Pentium II Processor Supply With 12V Power Input

Copyright © 1999

Rev. 1.1 11/99

PRODUCT DATABOOK 1996/1997

LX1662/62A, LX1663/63A

S

INGLE-CHIP PROGRAMMABLE

P RODUCTION DATA SHEET

BILL OF MATERIALS

LX1662 Bill of Materials (Refer to Product Highlight)

Ref Description Part Number / Manufacturer Qty.

PWM C

ONTROLLERS WITH

5-BIT DAC

C

2

C

1

C

8

C

3

C

5

L

1

L

2

Q

1

Q

2

R

1

1500µF, 6.3V capacitor MV-GX Sanyo 2
1500µF, 6.3V capacitor MV-GX Sanyo 4
680pF SMD Cap 1

0.1µF SMD Cap 1
1µF, 16V SMD Ceramic 1
5µF Inductor HM0096832 BI 1
1µF Inductor 1
MOSFET IRL3102 International Rectifier or equivalent 1
MOSFET IRL3303 International Rectifier or equivalent 1

2.5mΩ Sense Resistor (PCB trace) 1

U1 Controller IC LX1662CD Linfinity 1

Total 15

USING THE LX1662/63 DEVICES

The LX1662/63 devices are very easy to design with, requiring
only a few simple calculations to implement a given design. The
following procedures and considerations should provide effec­tive operation for virtually all applications. Refer to the Appli-
cation Information section for component reference designa­tors.

TIMING CAPACITOR SELECTION

The frequency of operation of the LX166x is a function of duty
cycle and OFF-time. The OFF-time is proportional to the timing
capacitor (which is shown as C8 in all application schematics in
this data sheet), and is modulated to minimize frequency
variations with duty cycle. The frequency is constant, during
steady-state operation, due to the modulation of the OFF-time.

The timing capacitor (CT) should be selected using the

following equation:

(1 - V

CT =

Where I

(recommended to be around 200kHz for optimal operation and

DIS

OUT /VIN

fS (1.52 - 0.29 * V

is fixed at 200µA and fS is the switching frequency

) * I

OUT

DIS

)

component selection).

When using a 5V input voltage, the switching frequency (fS)

can be approximated as follows:

I

CT = 0.621

DIS

*

f

S

Choosing a 680pF capacitor will result in an operating
frequency of 183kHz at V
is used, he capacitor value must be changed (the optimal timing

= 2.8V. When a 12V power input

OUT

capacitor for 12V input will be in the range of 1000-1500pF).

OUTPUT INDUCTOR SELECTION

L

1

The inductance value chosen determines the ripple current
present at the output of the power supply. Size the inductance
to allow a nominal ±10% swing above and below the nominal DC
load current, using the equation L = V
OFF-time, VL is the voltage across the inductor during the OFF­time, and ∆I is peak-to-peak ripple current in the inductor. Be
sure to select a high-frequency core material which can handle
the DC current, such as 3C8, which is sized for the correct power
level. Typical inductance values can range from 2 to 10µH.

Note that ripple current will increase with a smaller inductor.
Exceeding the ripple current rating of the capacitors could cause
reliability problems.

* ∆T/∆I, where ∆T is the

L

Copyright © 1999
Rev. 1.1 11/99

11

PRODUCT DATABOOK 1996/1997

LX1662/62A, LX1663/63A

S

INGLE-CHIP PROGRAMMABLE

P RODUCTION DATA SHEET

USING THE LX1662/63 DEVICES

PWM C

ONTROLLERS WITH

5-BIT DAC

INPUT INDUCTOR SELECTION

In order to cope with faster transient load changes, a smaller
output inductor is needed. However, reducing the size of the
output inductor will result in a higher ripple voltage on the input
supply. This noise on the 5V rail can affect other loads, such as
graphics cards. It is recommended that a smaller input inductor,
L

(1 - 1.5µH), is used on the 5V rail to filter out the ripple. Ensure

2

that this inductor has the same current rating as the output
inductor.

FILTER CAPACITOR SELECTION

C

1

The capacitors on the output of the PWM section are used to filter
the output current ripple, as well as help during transient load
conditions, and the capacitor bank should be sized to meet ripple
and transient performance specifications.

When a transient (step) load current change occurs, the output
voltage will have a step which equals the product of the Effective
Series Resistance (ESR) of the capacitor and the current step (∆I).
when current increases from low (in sleep mode) to high, the
output voltage will drop below its steady state value. In the
advanced microprocessor power supply, the capacitor should
usually be selected on the basis of its ESR value, rather than the
capacitance or RMS current capability. Capacitors that satisfy the
ESR requirement usually have a larger capacitance and current
capability than needed for the application. The allowable ESR can
be found by:

C1 FILTER CAPACITOR SELECTION (continued)

aluminum electrolytic, and have demonstrated reliability. The
Oscon series from Sanyo generally provides the very best
performance in terms of long term ESR stability and general
reliability, but at a substantial cost penalty. The MV-GX series
provides excellent ESR performance, meeting all Intel transient
specifications, at a reasonable cost. Beware of off-brand, very-low
cost filter capacitors, which have been shown to degrade in both
ESR and general electrolyte characteristics over time.

CURRENT LIMIT

Current limiting occurs when a sensed voltage, proportional to
load current, exceeds the current-sense comparator threshold
value. The current can be sensed either by using a fixed sense
resistor in series with the inductor to cause a voltage drop
proportional to current, or by using a resistor and capacitor in
parallel with the inductor to sense the voltage drop across the
parasitic resistance of the inductor.

The LX166x family offers two different comparator thresholds.
The LX1662 & 1663 have a threshold of 100mV, while the LX1662A
and LX1663A have a threshold of 60mV. The 60mV threshold is
better suited to higher current loads, such as a Pentium II or
Deschutes processor.

Sense Resistor

The current sense resistor, R1, is selected according to the formula:

ESR * (I

RIPPLE

+ ∆I) < V

EX

Where VEX is the allowable output voltage excursion in the
transient and I
as the LX166x series, have adaptive output voltage positioning,

is the inductor ripple current. Regulators such

RIPPLE

which adds 40mV to the DC set-point voltage — VEX is therefore
the difference between the low load voltage and the minimum
dynamic voltage allowed for the microprocessor.

Ripple current is a function of the output inductor value (L
and can be approximated as follows:

I

RIPPLE

VIN - V

fS * L

OUT

OUT

=

V

OUT

*

V

IN

OUT

Where fS is the switching frequency.

Electrolytic capacitors can be used for the output filter capaci­tor bank, but are less stable with age than tantalum capacitors. As
they age, their ESR degrades, reducing the system performance
and increasing the risk of failure. It is recommended that multiple
parallel capacitors are used so that, as ESR increases with age,
overall performance will still meet the processor's requirements.

There is frequently strong pressure to use the least expensive
components possible, however, this could lead to degraded long­term reliability, especially in the case of filter capacitors. Linfinity's
demo boards use Sanyo MV-GX filter capacitors, which are

R1 = V

Where V
for LX1662/63 and 60mV for LX1662A/63A) and I
current limit. Typical choices are shown below.

/ I

TRIP

TRIP

is the current sense comparator threshold (100mV

TRIP

TRIP

TABLE 2 - Current Sense Resistor Selection Guide

Sense Resistor Recommended

Load Value Controller

),

Pentium-Class Processor (<10A) 5mΩ LX1662 or LX1663
Pentium II Class (>10A) 2.5mΩ LX1662A or LX1663A

A smaller sense resistor will result in lower heat dissipation (I²R)
and also a smaller output voltage droop at higher currents.

There are several alternative types of sense resistor. The
surface-mount metal “staple” form of resistor has the advantage of
exposure to free air to dissipate heat and its value can be
controlled very tightly. Its main drawback, however, is cost. An
alternative is to construct the sense resistor using a copper PCB
trace. Although the resistance cannot be controlled as tightly, the
PCB trace is very low cost.

is the desired

12

Copyright © 1999

Rev. 1.1 11/99

PRODUCT DATABOOK 1996/1997

LX1662/62A, LX1663/63A

S

INGLE-CHIP PROGRAMMABLE

P RODUCTION DATA SHEET

USING THE LX1662/63 DEVICES

PWM C

ONTROLLERS WITH

5-BIT DAC

CURRENT LIMIT (continued)

PCB Sense Resistor

A PCB sense resistor should be constructed as shown in Figure

10. By attaching directly to the large pads for the capacitor and
inductor, heat is dissipated efficiently by the larger copper masses.
Connect the current sense lines as shown to avoid any errors.

Inductor

2.5m9

100mil Wide, 850mil Long

2.5mm x 22mm (2 oz/ft

Sense Resistor

2

copper)

Output
Capacitor Pad

Sense Lines

FIGURE 10 — Sense Resistor Construction Diagram

Recommended sense resistor sizes are given in the following

table:

TABLE 3 - PCB Sense Resistor Selection Guide

Copper Copper Desired Resistor Dimensions (w x l)
Weight Thickness Value mm inches

2

2 oz/ft

68µm 2.5m

5m

Ω

Ω

2.5 x 22 0.1 x 0.85

2.5 x 43 0.1 x 1.7

Loss-Less Current Sensing Using Resistance of Inductor

Any inductor has a parasitic resistance, RL, which causes a DC
voltage drop when current flows through the inductor. Figure 11
shows a sensor circuit comprising of a surface mount resistor, RS,
and capacitor, CS, in parallel with the inductor, eliminating the
current sense resistor.

L

R

L

Load

R

S

Current

Sense

C

S

R

S2

V

CS

Comparator

FIGURE 11 — Current Sense Circuit

CURRENT LIMIT

(continued)

The current flowing through the inductor is a triangle wave. If the
sensor components are selected such that:

L/R

= RS * C

L

S

The voltage across the capacitor will be equal to the current
flowing through the resistor, i.e.

VCS = ILR

L

Since VCS reflects the inductor current, by selecting the
appropriate RS and CS, VCS can be made to reach the comparator
voltage (60mV for LX166xA or 100mV for the LX166x) at the
desired trip current.

Design Example

(Pentium II circuit, with a maximum static current of 14.2A)

The gain of the sensor can be characterized as:

M

|T(

j

)|

R

L

L/RSC

S

M

1/R

SCSRL

/L

FIGURE 12 — Sensor Gain

The dc/static tripping current I

V

I

trip,S

trip

=

R

L

satisfies:

trip,S

Select L/RSCS ≤ RL to have higher dynamic tripping current
than the static one. The dynamic tripping current I

V

=

trip

L/(RSCS)

I

trip,d

General Guidelines for Selecting RS , CS, and R

V

trip

RL = Select: RS ≤ 10 kΩ

I

trip,S

and CS according to: CSn =

L

RL R

n

S

satisfies:

trip,d

L

The above equation has taken into account the current-de­pendency of the inductance.

The test circuit (Figure 6) used the following parameters:
RL = 3mΩ, RS = 9kΩ, CS = 0.1µF, and L is 2.5µH at 0A current.

Copyright © 1999
Rev. 1.1 11/99

13

PRODUCT DATABOOK 1996/1997

LX1662/62A, LX1663/63A

S

INGLE-CHIP PROGRAMMABLE

P RODUCTION DATA SHEET

USING THE LX1662/63 DEVICES

PWM C

ONTROLLERS WITH

5-BIT DAC

CURRENT LIMIT (continued)

In cases where RL is so large that the trip point current would
be lower than the desired short-circuit current limit, a resistor (R
can be put in parallel with C
of components is as follows:

R

L (Required)

R

L (Actual)

C

= =

S

Again, select (R

R

L (Actual)

=

* (RS2 // RS)

S2

, as shown in Figure 11. The selection

S

R

S2

RS2 + R

S

L

R

L (Actual)

L

*

//RS) < 10kΩ.

RS + R

RS2 * R

S2

S2

S

FET SELECTION

To insure reliable operation, the operating junction temperature
of the FET switches must be kept below certain limits. The Intel
specification states that 115°C maximum junction temperature
should be maintained with an ambient of 50°C. This is achieved
by properly derating the part, and by adequate heat sinking. One
of the most critical parameters for FET selection is the R
resistance. This parameter directly contributes to the power

DS

ON

dissipation of the FET devices, and thus impacts heat sink design,
mechanical layout, and reliability. In general, the larger the
current handling capability of the FET, the lower the RDS ON will
be, since more die area is available.

TABLE 4 - FET Selection Guide

This table gives selection of suitable FETs from International Rectifier.

Device R

IRL3803 6 83 30

IRL22203N 7 71 30

IRL3103 14 40 30
IRL3102 13 56 20
IRL3303 26 24 30
IRL2703 40 17 30

All devices in TO-220 package. For surface mount devices (TO-263 /
D2-Pak), add 'S' to part number, e.g. IRL3103S.

@ ID @ Max. Break-

DS(ON)

ΩΩ

10V (m

Ω)T

ΩΩ

= 100°C down Voltage

C

The recommended solution is to use IRL3102 for the high side
and IRL3303 for the low side FET, for the best combination of cost
and performance. Alternative FET’s from any manufacturer could
be used, provided they meet the same criteria for R

DS(ON)

.

Heat Dissipated In Upper MOSFET

The heat dissipated in the top MOSFET will be:

P

= (I2 * R

D

* Duty Cycle) + (0.51 * VIN * tSW * fS )

DS(ON)

FET SELECTION (continued)

For the IRL3102 (13mΩ R

)

will result in typical heat dissipation of 1.48W.

), converting 5V to 2.8V at 14A

DS(ON)

Synchronous Rectification – Lower MOSFET

The lower pass element can be either a MOSFET or a Schottky
diode. The use of a MOSFET (synchronous rectification) will result
in higher efficiency, but at higher cost than using a Schottky diode
(non-synchronous).

Power dissipated in the bottom MOSFET will be:

P

= I2 * R

D

[IRL3303 or 1.12W for the IRL3102]

* [1 - Duty Cycle] = 2.24W

DS(ON)

Catch Diode – Lower MOSFET

A low-power Schottky diode, such as a 1N5817, is recommended
to be connected between the gate and source of the lower
MOSFET when operating from a 12V-power supply (see Figure 9).
This will help protect the controller IC against latch-up due to the
inductor voltage going negative. Although latch-up is unlikely, the
use of such a catch diode will improve reliability and is highly
recommended.

Non-Synchronous Operation - Schottky Diode

A typical Schottky diode, with a forward drop of 0.6V will dissipate

0.6 * 14 * [1 – 2.8/5] = 3.7W (compared to the 1.1 to 2.2W dissipated
by a MOSFET under the same conditions). This power loss
becomes much more significant at lower duty cycles – synchro­nous rectification is recommended especially when a 12V-power
input is used. The use of a dual Schottky diode in a single TO-220
package (e.g. the MBR2535) helps improve thermal dissipation.

MOSFET GATE BIAS

The power MOSFETs can be biased by one of two methods:
charge pump or 12V supply connected to VC1.

1) Charge Pump (Bootstrap)

When 12V is supplied to the drain of the MOSFET, as in
Figure 9, the gate drive needs to be higher than 12V in order
to turn the MOSFET on. Capacitor C10 and diodes D2 & D
are used as a charge pump voltage doubling circuit to raise
the voltage of VC1 so that the TDRV pin always provides a
high enough voltage to turn on Q1. The 12V supply must
always be connected to VCC to provide power for the IC
itself, as well as gate drive for the bottom MOSFET.

2) 12V Supply

When 5V is supplied to the drain of Q1, a 12V supply should
be connected to both VCC and VC1.

3

Where t
and fS is the switching frequency.

is switching transition line for body diode (~100ns)

SW

14

Copyright © 1999

Rev. 1.1 11/99

PRODUCT DATABOOK 1996/1997

S

INGLE-CHIP PROGRAMMABLE

P RODUCTION DATA SHEET

USING THE LX1662/63 DEVICES

LAYOUT GUIDELINES - THERMAL DESIGN

A great deal of time and effort were spent optimizing the thermal
design of the demo boards. Any user who intends to implement
an embedded motherboard would be well advised to carefully
read and follow these guidelines. If the FET switches have been
carefully selected, external heatsinking is generally not required.
However, this means that copper trace on the PC board must now
be used. This is a potential trouble spot;
possible must be dedicated to heatsinking the FET switches, and
the diode as well if a non-synchronous solution is used.

In our VRM module, heatsink area was taken from internal
ground and VCC planes which were actually split and connected
with VIAS to the power device tabs. The TO-220 and TO-263
cases are well suited for this application, and are the preferred
packages. Remember to remove any conformal coating from all
exposed PC traces which are involved in heatsinking.

as much copper area as

PWM C

LX1662/62A, LX1663/63A

ONTROLLERS WITH

LX166x

5-BIT DAC

Input

5V or 12V

Output

FIGURE 13 — Power Traces

General Notes

As always, be sure to provide local capacitive decoupling close to
the chip. Be sure use ground plane construction for all high­frequency work. Use low ESR capacitors where justified, but be
alert for damping and ringing problems. High-frequency designs
demand careful routing and layout, and may require several
iterations to achieve desired performance levels.

Power Traces

To reduce power losses due to ohmic resistance, careful consid­eration should be given to the layout of traces that carry high
currents. The main paths to consider are:

■ Input power from 5V supply to drain of top MOSFET.

■ Trace between top MOSFET and lower MOSFET or Schottky

diode.

■ Trace between lower MOSFET or Schottky diode and
ground.

■ Trace between source of top MOSFET and inductor, sense
resistor and load.

RELATED DEVICES

LX1664/1665 - Dual Output PWM for µProcessor Applications

LX1668 - Triple Output PWM for µProcessor Applications

LX1553 - PWM for 5V - 3.3V Conversion

All of these traces should be made as wide and thick as
possible, in order to minimize resistance and hence power losses.
It is also recommended that, whenever possible, the ground, input
and output power signals should be on separate planes (PCB
layers). See Figure 13 – bold traces are power traces.

C5 Input Decoupling (VCC) Capacitor

Ensure that this 1µF capacitor is placed as close to the IC as
possible to minimize the effects of noise on the device.

Layout Assistance

Please contact Linfinity’s Applications Engineers for assistance
with any layout or component selection issues. A Gerber file
with layout for the most popular devices is available upon re­quest.

Evaluation boards are also available upon request. Please
check Linfinity's web site for further application notes.

Copyright © 1999
Rev. 1.1 11/99

Cyrix is a registered trademark and 6x86, Gx86 and M2 are trademarks of Cyrix Corporation. K6 is a trademark of AMD.

Power PC is a trademark of International Business Machines Corporation. Alpha is a trademark of Digital Equipment Corporation.

PRODUCTION DATA - Information contained in this document is proprietary to LinFinity, and is current as of publication date. This document
may not be modified in any way without the express written consent of LinFinity. Product processing does not necessarily include testing of
all parameters. Linfinity reserves the right to change the configuration and performance of the product and to discontinue product at any time.

Pentium is a registered trademark of Intel Corporation.

15