December 1997 - Linear Technology

Linear Technology Chronicle •

December 1997

A Showcase of Linear Technology’s Focus Products

Linear Technology Chronicle

December 1997 Vol. 6 No. 12

Product of the Month

, LTC and LT are registered trademarks of Linear Technology

Corporation. Burst Mode is a trademark of Linear Technology

Corporation.

Step-Down DC/DC

Converter Operates from

Single Li-Ion Cell

OUTPUT CURRENT (A)

0.01

EFFICIENCY (%)

100

95

90

85

80

75

70



0.1 1

1626 F01a



= 3.5V

L1 = 33µH

OUT

= 2.5V

SENSE

= 0.1Ω

= 270pF

Figure 1. LTC1626 Has an Efficiency

of 90% over a Load Current Range of

20mA to 500mA

The LTC

1626 is the first step-down

DC/DC converter that can operate at 100%

duty cycle from an input supply as low as

2.5V. Its integrated power switch has an

RDS(ON) of only 0.32Ω (VIN = 4.5V) and is

capable of delivering up to 600mA of output

current with a peak efficiency of 95%. Its

100% duty cycle and low dropout operation

extends the life of a single cell Lithium-Ion

battery while Burst Mode

operation main-

tains high efficiency at light loads. As shown

in Figure 1, the LTC1626 achieves greater

than 90% efficiency over a 20mA to 500mA

load range. Quiescent current is only 160µA

and drops down to just 0.5µA in shutdown.

It is targeted specifically at single cell Li-Ion

battery-powered applications such as PDAs,

GPSs, low power DSPs, digital cameras,

GSM cellular telephones or anything that

must operate from one Li-Ion cell or three to

four NiCd/NiMH cells.

The LTC1626 is a cost effective mono-

lithic solution that operates over the entire

voltage range of a Li-Ion cell (2.7V to 4.2V)

with a maximum input voltage of 7V (see

Figure 2). It’s ideal for those applications

that are changing from multiple NiCd or

NiMH cells to a single Li-Ion cell in order

to reduce the size and weight of the end

product.

The LTC1626 is offered in a 14-lead

SO package. Contact your local Linear

Technology sales office for a data sheet and

evaluation samples. For more information,

visit our web site at www.linear-tech.com.

Micropower Op Amp,

Comparator and

Reference Combined

in SO-8

The LTC1541 is a micropower op amp

with rail-to-rail outputs, a comparator and a

1.2V reference all combined in a single

SO-8 package. It is ideal for cost conscious

designs such as battery- or solar-powered

systems, GSM phones and IR receivers for

remote controls, where it is necessary to put

as much functionality (three different build-

ing blocks) into as little space as possible.

The part operates from a single 2.5V to

12.6V or dual ±1.25V to ±6.3V supply with

a typical quiescent current of just 5µA. Both

the op amp and comparator feature a com-

mon mode input voltage range that extends

from the negative supply to within 1.3V of

the positive supply. Figure 1 shows the

LTC1541 as a pilot light flame detector.

The reference output voltage of the

LTC1541 is 1.2V ±1% over the extended

temperature range. The output sources up to

2mA, sinks up to 20µA and can drive a by-

pass capacitor of up to 0.01µF without any

oscillations. The LTC1541’s op amp is in-

ternally compensated to be unity-gain stable.

LT1460H: First SOT-23 Voltage Reference with Guaranteed ≤20ppm/°C

Temperature Coefficient ...................................................................................................2

LT1316: Micropower Boost Regulator with Programmable Peak Current Limit

Extends Battery Life..........................................................................................................2

LTC1419: MUX 14-Bit ADC Without Software......................................................................... 3

LTC1659: Smallest 12-Bit DAC in 8-Pin MSOP Features ±0.5LSB Max DNL......................... 3

LT1510-5: 1.5A Constant-Current/Constant-Voltage Battery Charger in SSOP Package

Fits in Cell Phones ............................................................................................................4

Inside This Issue:

Figure 2. The LTC1626 as a High Efficiency 2.5V Step-Down Converter

PWR V

SGND

D1

MBRS130LT

0.1µF

 * COILTRONICS CTX33-4

 ** IRC 1206-R100F



†

 AVX TPSD476KO16



††

 AVX TPSC107M006R0150



270pF

470Ω

1000pF

3900pF

10k

1626 F01

10k

100pF

L*

33µHR

SENSE

**

0.1ΩV

OUT



2.5V

0.25A

OUT††



100µF

6.3V



2.7V TO 6V C

IN†



47µF

16V

LTC1626

SHDN

PGND

SENSE



SENSE

–



Continued on page 4

Linear Technology Chronicle •

December 1997

First SOT-23 Voltage Reference with Guaranteed

≤

20ppm/

C Temperature Coefficient

The LT

1460HCS3-2.5 and

LT1460HCS3-5 precision series 2.5V and

5V bandgap references are now available in

the ultrasmall SOT-23 package—the small-

est package available in the industry (Figure

1). These new references are trimmed to a

guaranteed initial accuracy of 0.2% and a

maximum temperature drift of only

20ppm/°C, less than half the best drift previ-

ously available in a SOT-23 reference. They

feature a low 100µA supply current (125µA

for the 5V version) and reverse-battery pro-

tection at the input. As shown in Figure 2,

the LT1460H’s typical accuracy shift is less

than 0.02% after being soldered onto a PC

board. No output capacitor is required for

stability, saving component costs and board

space. Output current of 20mA also makes

the LT1460 well-suited for use as a low

power precision voltage regulator. It is ideal

for use in portable meters, precision regula-

tors and in data conversion applications

where space and power are limited.

Three electrical grades of the LT1460 in

SOT-23 are offered. The prime grade (H)

offers an initial accuracy of 0.2% along with

the lowest TC available (20ppm/°C). The

next grade (J) offers the same low TC with

0.4% initial accuracy. The low cost (K)

grade offers 0.5% initial accuracy with a TC

of less than 50ppm/°C. In addition to the

3-lead SOT-23, the LT1460 is also offered in

8-pin PDIP, SO, MSOP and 3-lead TO-92

packages. For a data sheet and evaluation

samples, contact your local Linear

Technology sales office or visit our web

site at www.linear-tech.com for more

information.

Figure 1. The LT1460 in a SOT-23

Package Offers 0.2% Initial Accuracy

and a TC of 20ppm/

C. SOT-23 Package

Dimensions Are Approximately

3mm × 1.3mm × 1mm High

Figure 2. Typical Distribution of SOT-23

LT1460HC VOUT After IR Reflow Solder

per JEDEC JESD22-A112

The LT1316 is a micropower boost

DC/DC converter in a tiny MSOP package

that operates from an input voltage as low as

1.5V and has a quiescent current (IQ) of just

33µA. The peak switch current is user-

programmable from 30mA to 500mA by

selecting an inexpensive standard value

external resistor. This reduces the peak

inductor current and eases battery drain. In

shutdown mode, current drops to just 3µA.

It contains an independent low-battery

detector that remains active when the device

is shut down. Collectively, these features

Micropower Boost Regulator with Programmable

Peak Current Limit Extends Battery Life

LOAD CURRENT (mA)

0.1

EFFICIENCY (%)

1 10 100

1316 TA02

3.3VIN

2.5VIN

1.8VIN

The LT1316 also has a 30V switch

voltage which is useful for LCD bias appli-

cations that require a 28V bias supply. LCD

bias supplies often operate on just milliamps

of load current, so the peak switch current

needed in such an application is very low.

Setting the LT1316’s peak switch current

limit to match what is needed will greatly

increase battery life. Figure 2 shows the effi-

ciency vs load current for three input

voltages—3.3V, 2.5V and 1.8V.

The LT1316 is available in commercial

and industrial temperature range versions in

8-lead MSOP and SO packages. Contact

your local Linear Technology sales office for

a data sheet and evaluation samples or visit

our web site at www.linear-tech.com for

more information.

Figure 2. Efficiency vs Load

Current for the LT1316

SET

GND

FBSHDN

LBOLBI

LT1316 C2

47µF

NC NC

10k

C1

47µF

2 CELLS

L1

47µHD1 5V

50mA

D1: MOTOROLA MBR0520L

L1: SUMIDA CD43-470

1316 TA01

R1

1M

R2

324k

Figure 1. The LT1316 as a 2-Cell to 5V Step-Up Converter.

It Includes a Low-Battery Detector That Is Active in Shutdown

OUTPUT VOLTAGE (V)

2.490

DISTRIBUTION (%)

1460S3 TA02

02.500 2.510

LT1460HC LIMITS

make the LT1316 an excellent solution for

portable 2- to 4-cell battery-powered devices

needing boost or SEPIC configurations and

the longest possible battery operating

lifetime.

The programmable peak switch current

limit is set by a resistor from the RSET pin to

ground, as shown in Figure 1. This feature

also allows smaller sized capacitors and

inductors to be used in low current applica-

tions. Reduced peak input current further

improves system operating time from a bat-

tery supply, particularly with alkaline cells.

Linear Technology Chronicle •

December 1997

Application of the Month

The circuit at right uses hardware

instead of software routines to select multi-

plexer channels in a data acquisition

system. The circuit features the LTC1419

800ksps 14-bit ADC. It receives and con-

verts signals from a 74HC4051 8-channel

multiplexer. Three of the four output bits

from an additional circuit, the 74HC4520

dual 4-bit binary counter, are used to select

a multiplexer channel. A logic high power-

on or processor-generated reset is applied to

the counter’s Pin 7.

After the counter is cleared, the

multiplexer’s channel selection input is 000

and the input to channel is applied to the

LTC1419’s S/H input. The channel selec-

tion counter is clocked by the rising edge of

the convert start (CONVST ) signal that

initiates a conversion. As each CONVST

pulse increments the counter from 000 to

111, each multiplexer channel is individu-

ally selected and its input signal is applied

MUX 14-Bit ADC

Without Software

to the LTC1419. After each of the eight

channels has been selected, the counter rolls

over to zero and the process repeats. At any

time, the input multiplexer channel can be

reset to 0 by applying a logic high pulse to

Pin 7 of the counter.

Smallest 12-Bit DAC in

8-Pin MSOP Features

0.5LSB Max DNL

driving over 1000pF without oscillation. The

LTC1659 draws only 250µA (typ) quiescent

current from a single 5V supply. These fea-

tures make it well-suited for general

trimming applications, portable and battery-

powered equipment and in industrial control

systems where space is critical.

The LTC1659’s 3-wire cascadable

serial interface is compatible with SPI and

MICROWIRE

serial protocols. This eases

the connection to the serial interface of most

microprocessors and microcontrollers and

simplifies transmitting through isolation bar-

riers or to remote locations. Power-on reset

insures the DAC starts at zero scale after

power-up. The LTC1659’s Schmitt trigger

clock input permits a direct optocoupler

interface.

The LTC1659 is immediately available

in volume from stock in 8-lead MSOP or SO

packages. For a data sheet and evaluation

samples, contact your local Linear

Technology sales office or visit our web

site at www.linear-tech.com for more

information.

buffer amplifier and a 3-wire cascadable

serial interface, as shown in Figure 1. Its

DNL (differential nonlinearity) of only

±0.5LSB (max) guarantees 12-bit mono-

tonic performance, critical in control loop

applications. The LTC1659’s reference

input can be tied to the supply voltage,

2.7V to 5.5V, allowing a rail-to-rail output

swing to VCC. The rail-to-rail output ampli-

fier has improved capacitive load handling

over competing devices and is capable of

The LTC1659 is a micropower 12-bit

rail-to-rail VOUT DAC offered in an 8-pin

MSOP package—the smallest 12-bit DAC in

the industry. It includes a rail-to-rail output

–

12-BIT

DAC

2.7V TO 5.5V

GND

POWER-ON

RESET

TO

OTHER

DACS

12-BIT

SHIFT

REG

AND

DAC

LATCH

µP

REF

OUT

1659 TA01

CLK1

CS/LD3

7RAIL-TO-RAIL

VOLTAGE

OUTPUT

OUT



MICROWIRE is a trademark of National Semiconductor Corp.

Figure 1. The LTC1659 12-Bit Rail-to-Rail DAC Operates over a

3V to 5V Supply Range and Draws Only 250µA

1

2

3

4

5

6

7

8

9

10

11

12

13

28

27

26

25

24

23

22

21

20

19

18

17

16



–



REF

COMP

AGND

D13 (MSB)

D12

D11

D10

D9

D8

D7

D6

DGND



BUSY

CS

CONVST

RD

SHDN

D0

D1

D2

D3

D4

0.1µF

1µF

0.1µF

10µF

0.1µF

10µF10µF

14

13

12

11

1

2

7

15

2Q3

2Q2

2Q1

2Q0

2CE

1CLK

1CE

1CLEAR

2CLEAR

1Q0 1Q1 1Q2 1Q3

2CLK GND

0

1

2

3

4

5

6

13

14

15

12

1

5

2

AIN O

AIN 1

AIN 2

AIN 3

AIN 4

AIN 5

AIN 6

AIN 7



COM



INH

GND



16



3



6

8



A B C

3 4 5 6

74HC4051

74HC4520

LTC1419

–5V

DATA 0–13

CONVERT

CONTROL

BUSY

5V –5V

CLEAR

COUNT

1419 F00

Figure 1. This Simple Stand-Alone Circuit Requires No Software to

Sequentially Sample and Convert Eight Analog Signal Channels at 14-Bit

Resolution and 100ksps/Channel

Linear Technology Chronicle •

December 1997

Linear Technology Corporation • 1630 McCarthy Blvd. • Milpitas, CA 95035-7417 • (408) 432-1900 • FAX: (408) 434-0507 • www.linear-tech.com • For Literature Only: 1-800-4-LINEAR

Linear Technology

Products Are

Distributed By:

Almac/Arrow

Arrow/Schweber

Arrow/Zeus

Digi-Key

Electrosonic

Gerber Electronics

Farnell Electronics

Marshall Industries

Phase 1

1.5A Constant-Current/Constant-Voltage Battery

Charger in SSOP Package Fits in Cell Phones

The 500kHz LT1510-5 current mode

PWM battery charger delivers up to 1.5A

charging current from a 16-lead SSOP pack-

age and is small enough to integrate into the

tight confines of a miniature cell phone. It

provides the constant-voltage/constant-

current profile required by Li-Ion batteries

(see Figure 1) and the constant-current

charging needed by NiCd and NiMH batter-

ies. Its 500kHz operation allows use of very

small inductors and just a single one-tenth

watt resistor is needed to program charging

current from milliamps to 1.5A. In a 16-lead

SSOP (G-package), the LT1510 has a PCB

footprint equal to that of an SO-8. These

features make the device ideal for very small

cell phone designs that require a charger. It’s

also well-suited in handheld instruments and

electronic organizers where space and height

are very limited.

The LT1510, offered with switching

frequencies of 200kHz or 500kHz

(LT1510-5) and in a small outline package,

keeps the total PCB solution size very

small—less than 0.8in2(5.2cm2). The advan-

tage of a 500kHz switching regulator charger

IC is that the required inductor value is

smaller for a given charging current, com-

pared to the 200kHz version. New thin

inductors as small as 1.8mm in height can

now be used in space restricted cell phone

designs and other handheld instruments.

The LT1510’s wide 8V to 28V input

voltage range handles all wall adapter and

automotive battery inputs. An on-chip 2A

saturating power switch permits up to 90%

efficiency. Current can be monitored at

either battery terminal, allowing the nega-

tive terminal to be system ground. The

LT1510’s 0.5% accurate internal voltage

reference meets the critical constant-voltage

requirements of Li-Ion cells. The normal

charger-to-battery blocking diode is elimi-

nated since the LT1510 goes into a 3µA

sleep mode when the charging supply is

removed. A soft start capability avoids over-

loading wall adapter supplies at start-up.

The LT1510 is available in 16-lead

SSOP, SO and PDIP packages for constant-

current/constant-voltage chargers and is also

available in an SO-8 as a dedicated constant-

current charger. All devices are available

from stock in commercial and industrial tem-

perature versions. Contact your local Linear

Technology sales office for a data sheet and

evaluation samples. Visit our web site at

www.linear-tech.com for more information.

SW

BOOST

GND

SENSE



PROG



BAT

6.19k

8.2V TO 20V

R3

70.6k

0.25%

R4

100k

0.25%

†



2N7002



TOKIN OR MARCON CERAMIC SURFACE MOUNT

COILTRONICS TP3-100, 10µH, 2.2mm HEIGHT (0.8A CHARGING CURRENT)

COILTRONICS TP1 SERIES, 10µH, 1.8mm HEIGHT (<0.5A CHARGING CURRENT)

PANASONIC EEFCD1B220

OPTIONAL, SEE APPLICATIONS INFORMATION IN THE DATA SHEET

1510 F01

C1

0.22µF

*

10µF

L1**

10µHLT1510-5

D1

MBRM120T3

D3

MBRM120T3

D2

MMBD914L

OVP

OUT***



22µF4.2V

–

0.1µF1k

1µF300Ω

*

**



***

†

Figure 1. The LT1510 as a Li-Ion Constant-Current/Constant-Voltage Battery Charger

Uses a Single Resistor to Set the Full Charging Current (1.5A) to Within 5% Accuracy

LTC1541 from page 1

The comparator has ±3mV of hysteresis

to ensure clean output switching, even with

slow moving input signals. To minimize pin

count, the inverting input of the LTC1541

comparator is internally connected to the

reference output.

The LTC1541 is screened to the com-

mercial and industrial temperature ranges.

For a data sheet and evaluation samples,

contact your local Linear Technology sales

office. For more information, visit our web

site at www.linear-tech.com.

–

2N4391

2N4391 7

TPO610L

82.5k

= 8V TO 12V

= 9µs AT V

= 9V

6.2V

ZENER

0.1µF

OUTPUT

REF

= 1.2V

LTC1541 • TA01

–

10M

100k

–+

1/2 LTC1541

100k

TYPE R

Figure 1. In This Pilot Light Flame Detector Using an LTC1541, the

Thermocouple Signal Is Amplified by the Op Amp and Compared to the

Reference to Produce “Digital” Output