November 2000 - Linear Technology

Linear Technology Chronicle

• November 2000 1

A Showcase of Linear Technology’s Focus Products

Product of the Month

, LTC and LT are registered trademarks of Linear Technology

Corporation. Burst Mode and PowerPath are trademarks of

Linear Technology Corporation.

Linear Technology Chronicle

November 2000 Vol. 9 No. 11

Inside This Issue:

Low Voltage PowerPathTM Driver Switches from a 3.3V or 5V

Supply to Battery Backup—LTC1473L ................................................................................... 3

Dual 7ns Rail-to-Rail Input/Output Comparator with Latch Operates

On Supplies from 2.4V to 12V—LT1714................................................................................. 4

Lowest Noise 2.5V Shunt Reference Now in MS8—LT1009 .................................................. 4

Tiny, Current Mode Boost DC/DC Converters for

Loads Up to 10A—LTC3401/LTC3402/LTC1872/

LT1619

Table 1. New Boost Converters Are Tiny But Powerful

Input Max Switch Operating and

Boost Voltage Output Frequency Shutdown Micro

Converter Range Current** (Hz) Currents Package

LTC3401 0.5V* to 5V 500mA 300k to 3M 39µA, 1µA MS10

LTC3402 0.5V* to 5V 1A 300k to 3M 38µA, 1µA MS10

LTC1872 2.5V to 9.8V 2A

†

550k 270µA, 8µA SOT-23

LT1619 1.8V to 18V 10A

†

300k to 500k 140µA, 15µA MS8

*See text **Dependent upon input and output voltages

†

External switch

Four new switching regulator ICs pro-

vide boost voltage conversion in very small

spaces for portable and distributed power

systems (Table 1). The LTC

3401 and

LTC3402 regulate up to 500mA and 1A

outputs, respectively, from single cell

Li-Ion or alkaline sources. The LTC1872,

in a SOT-23 package, regulates up to 2A of

load current from various battery inputs and

wall adapters. The LT

1619 regulates up to

10A from a wide 1.9V to 18V input range.

The LTC1872 and LT1619 also function as

SEPIC buck-boost converters. The

LTC3401 and LTC3402 include power

switch transistors while the LTC1872 and

LT1619 use external power MOSFETs.

Each of the new regulators operates in

current mode for superior load regulation

and transient response. They include impor-

tant features such as cycle-by-cycle current

limiting, undervoltage lockout, adaptive

slope compensation and antiringing cir-

cuitry. Each regulator automatically shifts

into Burst Mode

operation in which the

MOSFETs switch intermittently, based on

load demand, to maintain high efficiency

when the output is lightly loaded. (Burst

Mode operation is user-selectable for the

LTC3401 and LTC3402.)

LTC3401 & LTC3402: to 3MHz Switch-

ing, 97% Efficient, <1V Input

The LTC3401 and LTC3402 offer the

highest power density available for single-

cell synchronous boost converters, provid-

ing a regulated output of up to 5W in only

0.05in

. Their very small size and high effi-

ciency (Figures 1 and 2) over a wide output

current range makes them valuable for com-

pact pagers, cordless phones, GPS receivers

and handheld instruments where small size

and extended battery operation are critical.

The switching regulators each incorporate a

0.16Ω N-channel MOSFET switch and a

0.18Ω synchronous rectifier to achieve

high efficiency. The LTC3402 delivers up

to 1A of load current (2A switch current)

with 95% efficiency while drawing only

38µA of supply current (in Burst Mode

16-Bit, 500ksps ADC

Offers No Missing Codes

Over Complete

Temperature Range—

LTC1608

The LTC1608 is a 16-bit, 500ksps ADC

that offers true 16-bit, no missing codes per-

formance over the entire industrial (–40°C to

85°C) temperature range with no pipeline

delay. Its speed, accuracy and no latency

architecture make the LTC1608 ideal for a

wide array of precision applications, includ-

ing high speed multiplexed data acquisition,

industrial process control and instrumenta-

tion. Its AC specs include 90dB S/(N + D)

and –100dB total harmonic distortion at a

sample rate of 500ksps (see Figure 1).

Continued on page 2

Continued on page 3

operation) for extended battery life. The

LTC3401 is a similar device with a 500mA

output capability.

Switching frequencies from 300kHz to

3MHz may be programmed with a timing

resistor, allowing designers to optimize

their circuits for RFI suppression, for the

highest efficiency or for a board footprint as

small as 0.16in

(100mm

). The LTC3401

FREQUENCY (kHz)

–40

–20

150 200

1608 TA02

–60

–80

50 100 250

–100

–120

–140

AMPLITUDE (dB)

SAMPLE

= 500kHz

= 98.754kHz

SINAD = 86.7dB

THD = –92.6dB

Figure 1. LTC1608 4096 Point FFT

Linear Technology Chronicle

• November 2000

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.

LTC3401/LTC3402/LTC1872/LT1619 from page 1

or LTC3402 oscillator can be synchronized

to an external clock for improved suppres-

sion of switching harmonics in sensitive

audio and IF bands. Burst Mode operation

is inhibited during synchronization or when

the MODE /SYNC pin is pulled low, pre-

venting interference from low frequency

ripple.

The LTC3401 and LTC3402 are

designed to start up at input voltages of

0.85V (typical). Once started, the IC oper-

ates from V

OUT

instead of V

. At this

point, the internal circuitry has no depen-

dency on the input voltage, eliminating the

requirement for a large input capacitor. The

input voltage can drop below 0.5V without

affecting the operation, provided that the

power source can supply sufficient energy

at that low voltage.

Other features include a power good

output and antiringing control. The devices

are available in the 10-lead thermally

enhanced MSOP package.

LTC1872: Output to 4A, SOT-23,

Constant 550kHz

The LTC1872 is a SOT-23 current

mode, step-up DC/DC controller with a

550kHz operating frequency. It provides the

SWV

4.7µH

OUT

909kLTC3402

SHDN

PGOOD

3402 TA01

MODE/SYNC

GND

549k

L1: COILCRAFT DO3316P-472

OSC

= 1MHz

30k

40.2k

470pF

47µF

3.3V

10µF

CELLS

20pF

Figure 1. 2-Cell to 3.3V at 1A Step-Up

Converter

OUT

(mA)

0.1

EFFICIENCY (%)

100

3402 TA02

110

100 1000

Burst Mode

OPERATION

1MHz

CONSTANT

FREQUENCY

= 2.4V WITH SCHOTTKY

Figure 2. Efficiency for the Circuit in

Figure 1

smallest solution for converting an input in

the range of 2.5V to 9.8V to a higher output

voltage at load currents of up to 2A. Appli-

cations include 1- and 2-cell Li-Ion-pow-

ered portable devices such as PDAs, GPS

systems and board-level boost conversion

for networking systems.

The device’s high operating frequency

(550kHz) reduces the value and size of the

inductor and capacitors (Figure 3). The

design may be packed in an area less than

110mm

. Low operating current of 270µA,

shutdown current of 8µA and operating effi-

ciency as high as 90% all help to extend

battery life.

The LTC1872 guarantees ±2.5% out-

put voltage accuracy. The output voltage is

limited only by the capability of the exter-

nal components. To prevent operation of

the N-channel MOSFET below safe input

voltage levels, an undervoltage lockout fea-

ture is incorporated into the LTC1872.

When the input supply voltage drops below

2V, the N-channel MOSFET and the con-

troller are turned off, except for the

undervoltage circuitry, which draws only a

few microamperes.

LT1619: Output to 10A, 90% Efficient,

1.9V to 18V Input Range, MSOP

The LT1619 is a fixed frequency, cur-

rent mode controller that implements boost,

SEPIC and flyback converters with a mini-

mum of external parts. Low parts count,

small size and high efficiency make the

LT1619 a perfect solution when a moderate

amount of 5V power is required in a pre-

dominately 3.3V system (Figure 4).

Conversion efficiency at heavy loads

surpasses competing devices by means of a

50mV current sense voltage. This low value

reduces energy loss in the sense resistor.

Burst Mode operation (Figure 5) keeps effi-

ciency high at light loads. The operating

frequency, typically 300kHz, may be syn-

chronized to an external clock of up to

500kHz. The device’s no-load quiescent cur-

rent of 140µA drops to 15µA in shutdown.

The internal rail-to-rail gate drive cir-

cuit is capable of switching a low side

N-channel power MOSFET with up to 60nC

of total gate charge. The upper supply of the

gate driver is brought out as a device pin

(DRV) for design flexibility. In boost con-

verters, the DRV pin can be tied to the con-

verter output (see Figure 4) if the minimum

input voltage is insufficient to fully enhance

the power MOSFET. The DRV pin can also

be powered from the input or from a separate

supply.

The LT1619 is not limited to low output

voltage supplies. It is also suitable for SLIC

voltage generation, for 5V to –48V conver-

sion in other telecommunications systems

and for SEPIC conversion in automotive

systems with an input range of 4V to 28V. A

few external components enable trickle start

from high voltage input sources, such as 36V

to 72V telecom supplies.

/RUN

LTC1872

10k

0.03Ω

412k

78.7k

4.7µH

220pF

C1: TAIYO YUDEN CERAMIC EMK325BJ106MNT

C2: AVX TPSE476M016R0150

D1: MOTOROLA MBRS340T3

L1: COILTRONICS UP1B-4R7

M1: Si9804DV

R1: DALE 0.25W

GND

1872 TA01

3NGATE

SENSE

–

10µF

10V

100pF

3.3V

OUT

2× 47µF

16V

M1 D1

Figure 3. 3.3V to 5V Boost Converter in

SOT-23 Provides 1A Output

0.1µF

15nF

220pF

3.3V

5.6µH

Si9804

OUT

2.2A

SENSE

0.01Ω

1619 F01

75k

37.4k

12.4k C1

22µF

C1: PANASONIC EEFCDOK220R

D1: MBRD835L

L1: COILCRAFT DO5022P-562

OUT

470µF

S/S

GND

DRV

GATE

SENSE

LT1619

LOAD CURRENT (mA)

EFFICIENCY (%)

1 100 1000

1619 F01a

70 10

Figure 4. High Efficiency 3.3V to 5V

DC/DC Converter Figure 5. Efficiency of the

Circuit in Figure 4

Linear Technology Chronicle

• November 2000 3

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.

Application of the Month

Low Voltage PowerPath Driver Switches from a

3.3V or 5V Supply to Battery Backup—LTC1473L

The LTC1608 operates from ±5V

supplies and has an input range of ±2.5V.

It dissipates only 270mW of power and of-

fers NAP (7mW) and SLEEP (10µW)

modes for further power reduction. This

easy-to-use ADC includes an internal clock

and a 15ppm/°C precision reference that

The LTC1473L solves the problem of

seamless power switching between 3.3V or

5V supplies and backup battery packs (3- or

4-cell NiMH) at high current levels. By

driving two sets of back-to-back N-channel

MOSFET switches, the LTC1473L routes

power to the input of a low voltage (3.3V to

10V) system efficiently and inexpensively.

Figure 1 is a schematic showing the

LTC1473L switch controller in conjunction

with an LT1512 battery charger. In this

application, the 4-cell NiMH battery is fully

charged by the 3.3V DC supply through the

LT1512 buck-boost converter to ensure that

it is always “topped off” and ready to pro-

vide backup power. R3 is set at 1Ω to

charge the NiMH battery pack at a constant

100mA rate.

In both applications, the value of

CTIMER determines the amount of time the

external NMOS switches are allowed to be

in current limit, and the value of RSENSE

determines the inrush current limit, which is

set at 2× to 3× of the maximum required out-

put current.

When V

falls below 2.5V, the

LTC1473L’s undervoltage lockout circuit

turns off both switches. With a built-in hys-

teresis of 100mV, the LTC1473L becomes

active again when V

rises above 2.6V.

Therefore, for 3.3V systems, small Schottky

diodes are used to power V

from both

DCIN and BAT1 so that the undervoltage

lockout circuit will not be falsely tripped.

Since the LTC1473L has an I

of less than

100µA at 3.3V, the drop across the

Schottky diode is less than 0.4V, leaving

enough room for a typical ±5% supply

tolerance.

Glitch-free and seamless transition of

power is crucial for maintaining normal

operation in low voltage electronic equip-

ment. The LTC1473L makes the transition

transparent and trouble free. (For systems

using supply voltages between 6V and 28V,

refer to the LTC1473 data sheet.)

can be overdriven externally. The

LTC1608’s parallel digitial interface can

communicate with both 3V and 5V logic,

enabling communication with a variety of

DSPs and microcontrollers.

The LTC1608 is available in the 36-pin

SSOP package in both the commercial and

IN1

IN2

DIODE

TIMER

GND

GA1

SAB1

GB1

SENSE

–

GA2

SAB2

GB2

LTC1473L

OUT

SENSE

0.04Ω

1µF

1mH

Si4936DY

BAT54C

100mA

MBRS130LT3

DCIN

3.3V

BAT1

4 NiMH

3.3V OR

BAT1

TIMER

4700pF

22µF

25V

47.5k

L1B*

L1A*

C2**

22µF

24Ω

22µF

25V

0.22µF

L1A, L1B ARE TWO 33µH WINDINGS ON A

SINGLE CORE: COILTRONICS CTX33-3

(561) 241-7876

TOKIN CERAMIC 1E22ZY5U-C203-F

(408) 432-8020

0.1µF

SYNC

AND/OR

SHDN

Si4936DY

1µF

12.4k

1Ω

FBS/S

GND

LT1512

GND

Figure 1. Battery Backup Circuit with LT1512 Battery Charger

LTC1608 from page 1

industrial temperature ranges. The

LTC1608 is pin compatible with the

LTC1604, a 16-bit, 333ksps ADC, offering

an easy upgrade path for applications

requiring higher speed.

Linear Technology Chronicle

• November 2000

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

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.

Dual 7ns Rail-to-Rail

Input/Output Comparator

with Latch Operates On

Supplies from 2.4V to

12V—LT1714

The LT1714 is the first dual compara-

tor that features 7ns propagation delay (see

Figure 1), a rail-to-rail input voltage range,

complimentary rail-to-rail CMOS/TTL

compatible outputs, internal data latches

and an operating supply range of 2.4V to

12V. This unique combination of features

greatly expands the variety of applications

in which the LT1714 can be used.

The LT1714’s fast response and 2.4V

operation, combined with its rail-to-rail

INPUT OVERDRIVE (mV)

PROPAGATION DELAY (ns)

6.5

7.0

7.5

PD+

PD–

30 50

1714 TA02

6.0

5.5

5.0 10 20 40

8.0

8.5

9.0

= 25°C

STEP

= 100mV

= 20mV

= 5V

–

= 0V

Figure 1. Propagation Delay

vs Input Overdrive

inputs and CMOS compatible outputs,

make it ideal for use in a wide variety of

low voltage digital applications such as

clock recovery or line receiver in broadband

communications systems. Additionally, the

LT1714’s 12V operational capability, low

(5mA/comparator) supply current and high

speed in a small SSOP package make it

well suited for use in automatic test equip-

ment. The dual internal latches make it suit-

able for use in data sampling circuits. With

rail-to-rail complimentary outputs that can

sink and source 10mA and output latches

with built-in hysteresis, the LT1714 simpli-

fies the design of discrete PWM circuits,

current sensing circuits for switching power

supplies, bang-bang controllers and a host

of other applications.

The LT1714 is available in a 16-pin

SSOP package that occupies the same foot-

print as a conventional SO-8 package in

both commercial and industrial temperature

ranges.

Table 1. Linear Technology’s Family of Precision References

Part Initial Supply

Number Accuracy Drift Current Comments Package

LT1009 0.2% 25ppm/°C * Low Noise Shunt Reference MS8, SO-8,

TO-92

LT1019 0.05% 3ppm/°C 0.65mA Precision Series Reference SO-8, DIP

LT1236 0.05% 5ppm/°C 0.8mA Precision Series Reference SO-8, DIP

LT1460 0.2% 20ppm/°C 115µA Micropower Precision SOT-23, MS8,

Series Reference SO-8

LT1461 0.04% 3ppm/°C35µA Micropower Precision SO-8

Series Reference

LT1634 0.05% 10ppm/°C10µA Micropower Precision MS8, SO-8

Shunt Reference

LT1790 0.05% 10ppm/°C60µA Micropower Low Dropout SOT-23

Reference

LTC1798 0.15% 40ppm/°C4µA Micropower Low Dropout SO-8

Reference

*Supply current for shunt reference depends on circuit conditions.

Lowest Noise 2.5V Shunt Reference Now In MS8—LT1009

The LT1009 is the lowest noise 2.5V

shunt reference available from Linear Tech-

nology. Now available in the MS8 package,

it is also the smallest (in both footprint and

height) of any of LTC’s shunt references.

The LT1009 is a precision trimmed

2.5V shunt regulator diode featuring a maxi-

mum initial tolerance of only ±5mV. This

0.2% reference tolerance is achieved by

on-chip trimming, which not only mini-

mizes the initial voltage tolerance but also

minimizes the temperature drift to a mere

25ppm/°C. The LT1009 excels in noise per-

formance, with only 13µV

RMS

typical out-

put noise.

Although no adjustments are needed

with the LT1009, a third terminal allows the

reference voltage to be adjusted ±5% to

calibrate out system errors. For a lower drift

2.5V reference, see the LT1019 data sheet

or refer to Table 1. The LT1009 is available

in the small MS8 package as well as SO-8

and TO-92 packages in commercial and

industrial temperature ranges.

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