Maxim MAX1676EUA, MAX1675EUA, MAX1674EUA Datasheet

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General Description

The MAX1674/MAX1675/MAX1676 compact, high-effi­ciency, step-up DC-DC converters fit in small µMAX
packages. They feature a built-in synchronous rectifier,
which improves efficiency and reduces size and cost
by eliminating the need for an external Schottky diode.
Quiescent supply current is only 16µA.

The input voltage ranges from 0.7V to V

OUT

, where

V

OUT

can be set from 2V to 5.5V. Start-up is guaran­teed from 1.1V inputs. The MAX1674/MAX1675/
MAX1676 have a preset, pin-selectable output for 5V or

3.3V. The outputs can also be adjusted to other volt­ages using two external resistors.

All three devices have a 0.3Ω N-channel MOSFET
power switch. The MAX1674 has a 1A current limit. The
MAX1675 has a 0.5A current limit, which permits the
use of a smaller inductor. The MAX1676 comes in a
10-pin µMAX package and features an adjustable cur­rent limit and circuitry to reduce inductor ringing.

________________________Applications

Pagers
Wireless Phones
Medical Devices
Hand-Held Computers
PDAs
RF Tags
1 to 3-Cell Hand-Held Devices

____________________________Features

♦ 94% Efficient at 200mA Output Current
♦ 16µA Quiescent Supply Current
♦ Internal Synchronous Rectifier (no external diode)
♦ 0.1µA Logic-Controlled Shutdown
♦ LBI/LBO Low-Battery Detector
♦ Selectable Current Limit for Reduced Ripple
♦ Low-Noise, Anti-Ringing Feature (MAX1676)
♦ 8-Pin and 10-Pin µMAX Packages
♦ Preassembled Evaluation Kit (MAX1676EVKIT)

MAX1674/MAX1675/MAX1676

High-Efficiency, Low-Supply-Current,

Compact, Step-Up DC-DC Converters

________________________________________________________________

Maxim Integrated Products

1

GNDLBO

SHDN

REF

1

2

8

7

OUT

LXLBI

FB

MAX1674
MAX1675

µMAX

TOP VIEW

3

4

6

5

1
2
3
4
5

10

9
8
7
6

OUT
LX
GND
BATTCLSEL

LBO

LBI

FB

MAX1676

µMAX

SHDNREF

MAX1674
MAX1675

INPUT

0.7V TO V

OUT

SHDN

LX

LBO

OUT

LBI

0.1µF

LOW-BATTERY
DETECT OUT

OFF

ON

REF

GND

FB

OUTPUT

3.3V, 5V, OR

ADJ (2V TO 5.5V)

UP TO 300mA

LOW-BATTERY

DETECT IN

PART

MAX1674EUA

-40°C to +85°C

TEMP. RANGE PIN-PACKAGE

8 µMAX

_______________Ordering Information

MAX1675EUA

-40°C to +85°C 8 µMAX

MAX1676EUB

-40°C to +85°C 10 µMAX

EVALUATION KIT

AVAILABLE

Typical Operating Circuit

Pin Configurations

19-1360; Rev 0; 7/98

MAX1674/MAX1675/MAX1676

High-Efficiency, Low-Supply-Current,
Compact, Step-Up DC-DC Converters

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(V

BATT

= 2V, FB = OUT (V

OUT

= 3.3V), RL= ˙∞, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

Supply Voltage (OUT to GND) ..............................-0.3V to +6.0V

Switch Voltage (LX to GND).....................-0.3V to (V

OUT

+ 0.3V)

Battery Voltage (BATT to GND).............................-0.3V to +6.0V

SHDN, LBO to GND ..............................................-0.3V to +6.0V

LBI, REF, FB, CLSEL to GND...................-0.3V to (V

OUT

+ 0.3V)

Switch Current (LX)...............................................-1.5A to +1.5A

Output Current (OUT) ...........................................-1.5A to +1.5A

Continuous Power Dissipation (T

A

= +70°C)

8-Pin µMAX (derate 4.1mW/°C above +70°C) .............330mW

10-Pin µMAX (derate 5.6mW/°C above +70°C) ...........444mW

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range.............................-65°C to +165°C

Lead Temperature (soldering, 10sec).............................+300°C

TA= +25°C, RL= 3kΩ (Note 1)

VLX= 0, 5.5V; V

OUT

= 5.5V

TA= +25°C

MAX1675, MAX1676 (CLSEL = GND)

MAX1674, MAX1676 (CLSEL = OUT)

ILX= 100mA

FB = OUT
(V

OUT

= 3.3V)

V

OUT

= 2V to 5.5V

I

REF

= 0 to 100µA

90 130

MAX1675,
MAX1676 (CLSEL = GND)

FB = OUT
FB = GND

I

REF

= 0

CONDITIONS

µA

0.05 1

I

LEAK

LX Leakage Current

A

0.4 0.5 0.65

I

LIM

0.80 1 1.20

LX Switch Current
Limit (NFET)

Ω

0.3 0.6

R

DS(ON)

Internal NFET, PFET
On-Resistance

V

1.274 1.30 1.326

FB, LBI Input Threshold

mV/V

0.08 2.5

V

REF_LINE

Reference Voltage Line
Regulation

mV

3 15

V

REF_LOAD

Reference Voltage Load
Regulation

mV/°C

0.024

TEMPCOReference Voltage Tempco

V

1.274 1.30 1.326

V

REF

Reference Voltage

V

0.9 1.1

Start-Up Voltage

V

1.1 5.5

V

IN

V

0.7

Minimum Input Voltage
Operating Voltage

150 220

FB = GND
(V

OUT

= 5V)

MAX1675,
MAX1676 (CLSEL = GND)

180 285

I

OUT

MAX1674,
MAX1676 (CLSEL = OUT)

mA

300 420

Steady-State Output Current
(Note 2)

mV/°C

-2

Start-Up Voltage Tempco

V

3.17 3.30 3.43

V

OUT

Output Voltage

4.80 5 5.20

MAX1674,
MAX1676 (CLSEL = OUT)

V

2 5.5

Output Voltage Range

UNITSMIN TYP MAXSYMBOLPARAMETER

MAX1674/MAX1675/MAX1676

High-Efficiency, Low-Supply-Current,

Compact, Step-Up DC-DC Converters

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS

(V

BATT

= 2V, FB = OUT, RL= ∞, TA= -40°C to +85°C, unless otherwise noted.) (Note 4)

Note 1: Start-up voltage operation is guaranteed with the addition of a Schottky MBR0520 external diode between the input and

output.

Note 2: Steady-state output current indicates that the device maintains output voltage regulation under load. See Figures 5 and 6.
Note 3: Device is bootstrapped (power to the IC comes from OUT). This correlates directly with the actual battery supply.

V

OUT

= 2V, I

LOAD

= 1mA

V

OUT

= 3.3V, I

LOAD

= 200mA

SHDN = GND

CONDITIONS

%

85

Efficiency

90

µA

0.1 1

Shutdown Current into OUT

UNITSMIN TYP MAXSYMBOLPARAMETER

MAX1676, V

BATT

= 2V

V

LBO

= 5.5V, V

LBI

= 5.5V

V

LBI

= 0, I

SINK

= 1mA

V

SHDN

= 0 or V

OUT

VFB= 1V, V

OUT

= 3.3V

MAX1676, CLSEL = OUT

V

LBI

= 1.4V

VFB= 1.4V

VFB= 1V, V

OUT

= 3.3V

0.8V

OUT

V

IH

0.2V

OUT

V

IL

CLSEL Input Voltage

V

0.8V

OUT

V

IH

0.2V

OUT

V

IL

SHDN Input Voltage

Ω88 150Damping Switch Resistance

µA

0.07 1

I

LBO

LBO Off Leakage Current

V

0.2 0.4

LBO Low Output Voltage

nA

0.07 50

I

SHDN

SHDN Input Current

µA

1.4 3

I

CLSEL

CLSEL Input Current

nA

1 50

I

LBI

LBI Input Current

nA

0.03 50

I

FB

FB Input Current

µs

0.8 1 1.2

t

OFF

LX Switch Off-Time

µs

3 4 7

t

ON

LX Switch On-Time

V

ELECTRICAL CHARACTERISTICS (continued)

(V

BATT

= 2V, FB = OUT (V

OUT

= 3.3V), RL= ˙∞, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

FB = GND

FB = OUT

VFB= 1V, V

OUT

= 3.3V

VFB= 1V, V

OUT

= 3.3V

SHDN = GND

VFB= 1.4V, V

OUT

= 3.3V

I

REF

= 0

MAX1675, MAX1676 (CLSEL = GND)

MAX1674, MAX1676 (CLSEL = OUT)

CONDITIONS

0.36 0.69

A

0.75 1.25

I

LIM

LX Switch Current
Limit (NFET)

V2.20 5.5Output Voltage Range

V

4.75 5.25

3.13 3.47

V

OUT

Output Voltage

µs0.75 1.25t

OFF

LX Switch Off-Time

µs2.7 7.0t

ON

LX Switch On-Time

µA1Shutdown Current into OUT

µA40

Operating Current into OUT
(Note 3)

V1.2675 1.3325V

REF

Reference Voltage

V1.2675 1.3325FB, LBI Thresholds

Ω0.6R

DS(ON)

Internal NFET, PFET
On-Resistance

UNITSMIN MAXSYMBOLPARAMETER

VFB= 1.4V, V

OUT

= 3.3V µA

16 35

Operating Current into OUT
(Note 3)

MAX1674/MAX1675/MAX1676

High-Efficiency, Low-Supply-Current,
Compact, Step-Up DC-DC Converters

4 _______________________________________________________________________________________

Typical Operating Characteristics

(L = 22µH, CIN= 47µF, C

OUT

= 47µF0.1µF, C

REF

= 0.1µF, TA= +25°C, unless otherwise noted.)

V

LBO

= 5.5V, V

LBI

= 5.5V

V

SHDN

= 0 or V

OUT

MAX1676, CLSEL = OUT

CONDITIONS

µA1I

LBO

LBO Off Leakage Current

nA75I

SHDN

SHDN Input Current

µA3I

CLSEL

CLSEL Input Current

UNITSMIN MAXSYMBOLPARAMETER

ELECTRICAL CHARACTERISTICS (continued)

(V

BATT

= 2V, FB = OUT, RL= ∞, TA= -40°C to +85°C, unless otherwise noted.) (Note 4)

Note 4: Specifications to -40°C are guaranteed by design, not production tested.

100

0

0.01 0.1 1 10 100 1000

EFFICIENCY vs. LOAD CURRENT

20

30

10

MAX1674 toc01

LOAD CURRENT (mA)

EFFICIENCY (%)

40

50

60

70

90
80

VIN = 1.2V

V

OUT

= 5V

I

LIMIT

= 500mA

VIN = 2.4V

VIN = 3.6V

100

0

0.01 0.1 1 10 100 1000

EFFICIENCY vs. LOAD CURRENT

20

30

10

MAX1674 toc02

LOAD CURRENT (mA)

EFFICIENCY (%)

40

50

60

70

90
80

VIN = 1.2V

V

OUT

= 5V

I

LIMIT

= 1A

VIN = 2.4V

VIN = 3.6V

100

0

0.01 0.1 1 10 100 1000

EFFICIENCY vs. LOAD CURRENT

20

30

10

MAX1674 toc03

LOAD CURRENT (mA)

EFFICIENCY (%)

40

50

60

70

90
80

VIN = 1.2V

V

OUT

= 3.3V

I

LIMIT

= 500mA

VIN = 2.4V

100

0

0.01 0.1 1 10 100 1000

EFFICIENCY vs. LOAD CURRENT

20

30

10

MAX1674 toc04

LOAD CURRENT (mA)

EFFICIENCY (%)

40

50

60

70

90
80

VIN = 1.2V

V

OUT

= 3.3V

I

LIMIT

= 1A

VIN = 2.4V

1.290

1.292

1.296

1.294

1.298

1.300

-40 0-20 20 40 60 80 100

REFERENCE OUTPUT VOLTAGE

vs. TEMPERATURE

MAX1674 toc05

TEMPERATURE (°C)

REFERENCE OUTPUT VOLTAGE (V)

I

REF

= 0

I

REF

= 100µA

MAX1674/MAX1675/MAX1676

High-Efficiency, Low-Supply-Current,

Compact, Step-Up DC-DC Converters

_______________________________________________________________________________________

5

0

40
20

100

80
60

140
120

160

0 1.5 2.00.5 1.0 2.5 3.0 3.5 4.0 4.5

NO-LOAD BATTERY CURRENT
vs. INPUT BATTERY VOLTAGE

MAX1674toc07

INPUT BATTERY VOLTAGE (V)

INPUT BATTERY CURRENT (µA)

I

LIMIT

= 1A, 5.0V

I

LIMIT

= 0.5A, 5.0V

I

LIMIT

= 0.5A, 3.3V

I

LIMIT

= 1A, 3.3V

1.8

0

0.01 1 100.1 100

START-UP VOLTAGE

vs. LOAD CURRENT

0.2

0.4

MAX1674toc08

LOAD CURRENT (mA)

START-UP VOLTAGE (V)

0.8

0.6

1.0

1.2

1.4

1.6

WITHOUT DIODE

WITH 1N5817

-1.0

-0.6

-0.8

-0.2

-0.4

0.2
0

0.4

0.8

0.6

1.0

1 2.0 2.5 3.01.5 3.5 4.0 4.5 5.0 5.5

SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE

MAX167toc09

SUPPLY VOLTAGE (V)

SHUTDOWN CURRENT (µA)

0

0.4

0.2

0.8

0.6

1.2

1.0

1.4

0 1.0 1.50.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

SHUTDOWN THRESHOLD

vs. SUPPLY VOLTAGE

MAX1674TOC10

SUPPLY VOLTAGE (V)

SHUTDOWN THRESHOLD (V)

0

200
100

500

300

400

800
700
600

900

1.0 2.01.5 2.5 3.0 3.5 4.0 4.5

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE (V

OUT

= 5V)

MAX1674toc11

INPUT VOLTAGE (V)

MAXIMUM OUTPUT CURRENT (mA)

1A CURRENT LIMIT

0.5A CURRENT LIMIT

0

200
100

400
300

600
500

800
700

1.0 1.4 1.61.2 1.8 2.0 2.2 2.4 2.6 2.8 3.0

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE (V

OUT

= 3.3V)

MAX1674toc12

INPUT VOLTAGE (V)

MAXIMUM OUTPUT CURRENT (mA)

0.5A CURRENT LIMIT

1A CURRENT LIMIT

Typical Operating Characteristics (continued)

(L = 22µH, CIN= 47µF, C

OUT

= 47µF0.1µF, C

REF

= 0.1µF, TA= +25°C, unless otherwise noted.)

1µs/div

HEAVY-LOAD SWITCHING WAVEFORMS

MAX1674 TOC13

V

LX

5V/div
I

LX

0.5A/div

V

OUT

AC COUPLED
100mV/div

V

IN

= 2.4V

V

OUT

= 5.0V

0

0.4

0.2

0.8

0.6

1.0

1.2

2.0 3.0 3.52.5 4.0 4.5 5.0

LX CURRENT LIMIT

vs. OUTPUT VOLTAGE

MAX1674toc14

OUTPUT VOLTAGE (V)

I

LIM

(A)

MAX1674, MAX1676 (CLSEL = OUT)

MAX1675, MAX1676 (CLSEL = GND)

0

0.15

0.10

0.05

0.25

0.20

0.35

0.30

0.45

0.40

-60 -20

-40

0 20 40 60 80 100

SWITCH RESISTANCE vs. TEMPERATURE

MAX1674toc13.5

TEMPERATURE (°C)

RESISTANCE (Ω)

P-CHANNEL

N-CHANNEL

10µs/div

LINE-TRANSIENT RESPONSE

MAX1674 TOC15

V

IN

2V TO 3V
1V/div

V

OUT

AC COUPLED
100mV/div

I

LOAD

100mA

5µs/div

LOAD-TRANSIENT RESPONSE

MAX1674 TOC16

I

OUT

200mA/div

V

OUT

50mV/div
AC
COUPLED

V

IN

= 2.4V

V

OUT

= 3.3V

500µs/div

EXITING SHUTDOWN

MAX1674 TOC17

V

SHDN

2V/div

V

OUT

2V/div

MAX1674/MAX1675/MAX1676

High-Efficiency, Low-Supply-Current,
Compact, Step-Up DC-DC Converters

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(L = 22µH, CIN= 47µF, C

OUT

= 47µF0.1µF, C

REF

= 0.1µF, TA= +25°C, unless otherwise noted.)

Pin Description

PIN

NAME FUNCTION

MAX1674
MAX1675

MAX1676

1 1 FB

Dual-Mode™ Feedback Input. Connect to GND for +5.0V output.
Connect to OUT for +3.3V output. Use a resistor network to set the
output voltage from +2.0V to +5.5V.

2 2 LBI Low-Battery Comparator Input. Internally set to trip at +1.30V.

3 3

LBO

Open-Drain Low-Battery Comparator Output. Output is low when
V

LBI

is <1.3V. LBO is high impedance during shutdown.

— 4 CLSEL

Current-Limit Select Input. CLSEL = OUT sets the current limit to 1A.

CLSEL = GND sets the current limit to 0.5A.
4 5 REF 1.3V Reference Voltage. Bypass with a 0.1µF capacitor.
5 6

SHDN

Shutdown Input. High = operating, low = shutdown.

— 7 BATT

Battery Input and Damping Switch Connection. If damping switch is

unused, leave BATT unconnected.
6 8 GND Ground
7 9 LX N-Channel and P-Channel Power MOSFET Drain
8 10 OUT Power Output. OUT provides bootstrap power to the IC.

Dual-Mode is a trademark of Maxim Integrated Products.

Detailed Description

The MAX1674/MAX1675/MAX1676 compact, step-up
DC-DC converters start up with voltages as low as 0.9V
and operate with an input voltage down to 0.7V.
Consuming only 16µA of quiescent current, these
devices offer a built-in synchronous rectifier that
reduces cost by eliminating the need for an external
diode and improves overall efficiency by minimizing
losses in the circuit (see

Synchronous Rectification

sec­tion for details). The internal MOSFET resistance is typi­cally 0.3Ω, which minimizes losses. The current limit of
the MAX1674 and MAX1675 are 1A and 0.5A, respec­tively. The MAX1675’s lower current limit allows the use
of a physically smaller inductor in space-sensitive
applications. The MAX1676 features a circuit that elimi­nates noise due to inductor ringing. In addition, the
MAX1676 offers a selectable current limit (0.5A or 1A)
for design flexibility.

PFM Control Scheme

A unique minimum-off-time, current-limited, pulse-fre­quency-modulation (PFM) control scheme is a key fea­ture of the MAX1674/MAX1675/MAX1676. This scheme

combines the high output power and efficiency of a
pulse-width-modulation (PWM) device with the ultra-low
quiescent current of a traditional PFM (Figure 1). There
is no oscillator; a constant-peak-current limit in the
switch allows the inductor current to vary between this
peak limit and some lesser value. At light loads, the
switching frequency is governed by a pair of one-shots
that set a typical minimum off-time (1µs) and a typical
maximum on-time (4µs). The switching frequency
depends upon the load and the input voltage, and can
range up to 500kHz. The peak current of the internal N­channel MOSFET power switch is fixed at 1A
(MAX1674), at 0.5A (MAX1675), or is selectable
(MAX1676). Unlike conventional pulse-skipping DC-DC
converters (where ripple amplitude varies with input
voltage), ripple in these devices does not exceed the
product of the switch current limit and the filter-capaci­tor equivalent series resistance (ESR).

Synchronous Rectification

The internal synchronous rectifier eliminates the need
for an external Schottky diode, thus reducing cost and
board space. During the cycle off-time, the P-channel
MOSFET turns on and shunts the MOSFET body diode.

MAX1674/MAX1675/MAX1676

High-Efficiency, Low-Supply-Current,

Compact, Step-Up DC-DC Converters

_______________________________________________________________________________________ 7

MAX1674
MAX1675
MAX1676

ONE-SHOT

TRIG

Q

F/F

R

S

Q

ONE-SHOT

TRIG

Q

CURRENT-LIMIT
AMPLIFIER

ERROR
AMPLIFIER

LOW-BATTERY
COMPARATOR

REFERENCE

REF

FB

V

IN

47µF

47µF

R1

200Ω

R5

R6

DAMPING

SWITCH

22µH

BATT

(MAX1676)

GND

LX

OUT

0.1µF

0.1µF

V

OUT

R4

LBI

LBO

R2

100k

R3

V

IN

V

OUT

CLSEL

(MAX1676)

SHDN

MINIMUM
OFF-TIME

ONE-SHOT

ZERO
CROSSING
AMPLIFIER

EN

MAXIMUM
ON-TIME
ONE-SHOT

P

N

Figure 1. Simplified Functional Diagram

MAX1674/MAX1675/MAX1676

As a result, the synchronous rectifier significantly
improves efficiency without the addition of an external
component. Conversion efficiency can be as high as
94%, as shown in the

Typical Operating Characteristics

.
For low-voltage inputs from single cells (Alkaline, NiCd,
or NiMH), use an external Schottky diode such as the
1N5817 to ensure start-up.

Voltage Reference

The voltage at REF is nominally +1.30V. REF can
source up to 100µA to external circuits. The reference
maintains excellent load regulation (see

Typical Oper-

ating Characteristics

). A bypass capacitor of 0.1µF is

required for proper operation.

Shutdown

The device enters shutdown when V

SHDN

is low.
During shutdown, the body diode of the P-channel
MOSFET allows current flow from the battery to the out­put. V

OUT

falls to approximately VIN- 0.6V and LX
remains high impedance. The capacitance and load at
OUT determine the rate at which V

OUT

decays.
Shutdown can be pulled as high as 6V, regardless of
the voltage at OUT.

Current Limit Select Pin (MAX1676)

The MAX1676 allows a selectable inductor current limit
of either 0.5A or 1A. This allows flexibility in designing
for higher current applications or for smaller, compact
designs. Connect CLSEL to OUT for 1A or to GND for

0.5A. CLSEL draws 1.4µA when connected to OUT.

BATT/Damping Switch (MAX1676)

The MAX1676 is designed with an internal damping
switch to minimize ringing at LX. The damping switch
connects an external resistor (R1) across the inductor
when the inductor’s energy is depleted (Figure 2).
Normally, when the energy in the inductor is insufficient
to supply current to the output, the capacitance and
inductance at LX form a resonant circuit that causes
ringing. The ringing continues until the energy is dissi­pated through the series resistance of the inductor. The
damping switch supplies a path to quickly dissipate this
energy, minimizing the ringing at LX. Damping LX ring­ing does not reduce V

OUT

ripple, but does reduce EMI.
R1 = 200Ω works well for most applications while reduc­ing efficiency by only 1%. Larger R1 values provide less
damping, but have less impact on efficiency. Generally,
lower values of R1 are needed to fully damp LX when
the V

OUT/VIN

ratio is high (Figures 2, 3, and 4).

High-Efficiency, Low-Supply-Current,
Compact, Step-Up DC-DC Converters

8 _______________________________________________________________________________________

MAX1676

DAMPING
SWITCH

BATT

R1
200Ω

LX

OUT

22µH

V

IN

0.1µF

47µF

V

OUT

Figure 2. Simplified Diagram of Inductor Damping Switch

2µs/div

V

LX

1V/div

Figure 3. LX Ringing Without Damping Switch

2µs/div

V

LX

1V/div

Figure 4. LX Waveform with Damping Switch (with 200

Ω

external resistor)

Selecting the Output Voltage

V

OUT

can be set to 3.3V or 5.5V by connecting the FB

pin to GND (5V) or OUT (3.3V) (Figures 5 and 6).
To adjust the output voltage, connect a resistor-divider

from V

OUT

to FB to GND (Figure 7). Choose a value
less than 260kΩ for R6. Use the following equation to
calculate R5:

R5 = R6 [(V

OUT

/ V

REF

) - 1]

where V

REF

= +1.3V and V

OUT

may range from 2V to
5V. The input bias current of FB has a maximum value
of 50nA which allows large-value resistors (R6 ≤ 260kΩ)
to be used.

Low-Battery Detection

The MAX1674/MAX1675/MAX1676 contain an on-chip
comparator for low-battery detection. If the voltage at
LBI falls below the internal reference voltage (1.30V),
LBO (an open-drain output) sinks current to GND. The
low-battery monitor threshold is set by two resistors, R3
and R4 (Figures 5, 6, and 7). Since the LBI current is
less than 50nA, large resistor values (R4 ≤ 260kΩ) can
be used to minimize loading of the input supply.
Calculate R3 using the following equation:

R3 = R4 [(V

TRIP

/ V

REF

) - 1]

for V

TRIP

≥ 1.3V. V

TRIP

is the level where the low-battery

detector output goes low, and V

REF

is the internal

1.30V reference. Connect a pull-up resistor of 100kΩ or
greater from LBO to OUT when driving CMOS circuits.
LBO is an open-drain output, and can be pulled as
high as 6V regardless of the voltage at OUT. When LBI
is above the threshold, the LBO output is high imped­ance. If the low-battery comparator is not used, ground

MAX1674/MAX1675/MAX1676

High-Efficiency, Low-Supply-Current,

Compact, Step-Up DC-DC Converters

_______________________________________________________________________________________ 9

MAX1674
MAX1675
MAX1676

BATT
(MAX1676)

V

IN

LBI

REF

GND

R3

R1

200Ω

R4

R2
100k

47µF

10V

22µH

0.1µF

LX

LBO

0.1µF

47µF

+3.3V
200mA

V

OUT

LOW-BATTERY

OUTPUT

FB

SHDN

OUT

CLSEL

(MAX1676)

Figure 5. Preset Output Voltage of +3.3V

MAX1674
MAX1675
MAX1676

BATT
(MAX1676)

V

IN

LBI

REF

GND

R6

R5

R3

R1

200Ω

R4

R2
100k

22µH

47µF

0.1µF

LX

LBO

OUTPUT
2V to 5.5V

FB

SHDN

OUT

CLSEL

(MAX1676)

LOW­BATTERY
OUTPUT

0.1µF

47µF

Figure 7. Setting an Adjustable Output

MAX1674
MAX1675
MAX1676

BATT
(MAX1676)

V

IN

LBI

REF

GND

R3

R1

200Ω

R4

R2
100k

22µH

47µF

0.1µF

LX

LBO

0.1µF

47µF

OUTPUT

5.0V,
150mA

FB

SHDN

OUT

CLSEL

(MAX1676)

LOW­BATTERY
OUTPUT

Figure 6. Preset Output Voltage of +5V

MAX1674/MAX1675/MAX1676

LBI and LBO. For V

TRIP

less than 1.3V, configure the
comparator as shown in Figure 8. Calculate the value of
the external resistors R3 and R4 as follows:

R3 = R4(V

REF

- V

TRIP

) / (V

OUT

- V

REF

)

Since the low-battery comparator is noninverting, exter­nal hysteresis can be added by connecting a resistor
between LBO and LBI as shown in Figure 9. When LBO
is high, the series combination of R2 and R7 source
current into the LBI summing junction.

Applications Information

Inductor Selection

An inductor value of 22µH performs well in most appli­cations. The MAX1674/MAX1675/MAX1676 will also
work with inductors in the 10µH to 47µH range. Smaller
inductance values typically offer a smaller physical size
for a given series resistance, allowing the smallest
overall circuit dimensions. However, due to higher peak
inductor currents, the output voltage ripple (I

PEAK

x
output filter capacitor ESR) also tends to be higher.
Circuits using larger inductance values exhibit higher
output current capability and larger physical dimen­sions for a given series resistance. The inductor’s incre­mental saturation current rating should be greater than
the peak switch-current limit, which is 1A for the

MAX1674, 500mA for the MAX1675, and 1A or 0.5A for
the MAX1676. However, it is generally acceptable to
bias the inductor into saturation by as much as 20%,
although this will slightly reduce efficiency. Table 1 lists
suggested components.

The inductor’s DC resistance significantly affects effi­ciency. See Table 2 for a comparison of inductor speci­fications. Calculate the maximum output current as
follows:

where I

OUT(MAX)

= maximum output current in amps

V

BATT

= input voltage
L = inductor value in µH
η= efficiency (typically 0.9)
t

OFF

= LX switch’s off-time in µs
RP= resistance of P-channel MOSFET in Ω
I

LIM

= 0.5A or 1.0A

I

V I

V V

L

t

R

V

OUT MAX

BATT LIM

OUT BATT

OFF

P

OUT

( )

=

+





















– /

–

1 2 η

High-Efficiency, Low-Supply-Current,
Compact, Step-Up DC-DC Converters

10 ______________________________________________________________________________________

MAX1674
MAX1675
MAX1676

BATT
(MAX1676)

V

IN

LBI

REF

GND

R3

R1

200Ω

R4

22µH

47µF

0.1µF

LX

LBO

V

OUT

FB

R2
100k

SHDN

OUT

CLSEL

(MAX1676)

LOW­BATTERY
OUTPUT

0.1µF

47µF

Figure 8. Setting Resistor Values for the Low-Battery Indicator
when V

IN

< 1.3V

MAX1674
MAX1675
MAX1676

LBI

GND

V

TRIP

(VH, VL)

R3

R4

R7

V

H

IS THE UPPER TRIP LEVEL

VL IS THE LOWER TRIP LEVEL

WHERE

R2

100k

LBO

OUT

V

OUT

0.1µF

47µF

V = 1.3V

V = 1.3V

H

L

( )

+ +











( )

+ −

−
+











( . )

( . ) ( )

1

373

4

1

3
4

1 3 3

1 3 2 7

RRR

R

R
R

V V R

V R R

OUT

Figure 9. Adding External Hysteresis to the Low-Battery
Indicator

Capacitor Selection

A 47µF, 10V surface-mount tantalum (SMT) output filter
capacitor provides 80mV output ripple when stepping
up from 2V to 5V. Smaller capacitors (down to 10µF
with higher ESRs) are acceptable for light loads or in
applications that can tolerate higher output ripple.
Values in the 10µF to 100µF range are recommended.
The equivalent series resistance (ESR) of both bypass
and filter capacitors affects efficiency and output rip­ple. Output voltage ripple is the product of the peak

inductor current and the output capacitor ESR. Use
low-ESR capacitors for best performance, or connect
two or more filter capacitors in parallel. Low-ESR, SMT
tantalum capacitors are currently available from
Sprague (595D series) AVX (TPS series) and other
sources. Ceramic surface-mount and Sanyo OS-CON
organic-semiconductor through-hole capacitors also
exhibit very low ESR, and are especially useful for oper­ation at cold temperatures. See Table 3 for a list of sug­gested component suppliers.

MAX1674/MAX1675/MAX1676

High-Efficiency, Low-Supply-Current,

Compact, Step-Up DC-DC Converters

______________________________________________________________________________________ 11

PRODUCTION

METHOD

INDUCTORS CAPACITORS

RECTIFIERS
(OPTIONAL)

Surface Mount

Sumida CD43 series
Sumida CD54 series
Coilcraft DT1608C
Coilcraft DO1608C
Coiltronics Uni-PAC
Murata LQH4 series

Sprague 593D series
Sprague 595D series
AVX TPS series
ceramic

Motorola MBR0530
Nihon EC 15QS02L

Miniature Through-Hole Sumida RCH654-220 Sanyo OS-CON series —

Table 1. Suggested Components

Table 2. Surface-Mount Inductor
Specifications

MANUFACTURER

PART NUMBER

µH Ω (max) I

PEAK

(A)

HEIGHT

(mm)

Coilcraft DT1608C-103 10 0.095 0.7 2.92
Coilcraft DO1608C-153 15 0.200 0.9 2.92
Coilcraft DO1608C-223 22 0.320 0.7 2.92
Coiltronics UP1B-100 10 0.111 1.9 5.0

Table 3. Component Suppliers

COMPANY PHONE FAX

AVX USA [phone] USA [phone]
Coilcraft USA [phone] USA [phone]
Coiltronics USA [phone] USA [phone]

Murata

USA [phone]

[phone]

USA [phone]

Nihon

USA [phone]

Japan 81-3-3494-7411

USA [phone]
Japan 81-3-3494-7414

Motorola

USA [phone]

[phone]

USA [phone]

Sanyo

USA [phone]

Japan 81-7-2070-6306

USA [phone]

Japan 81-7-2070-1174

Sumida

USA [phone]

Japan 81-3-3607-5111

USA [phone]

Japan 81-3-3607-5144

Taiyo Yuden USA [phone] USA [phone]

Sprague USA [phone] USA [phone]

Coiltronics UP1B-150 15 0.175 1.5 5.0
Coiltronics UP1B-220 22 0.254 1.2 5.0
Murata LQH4N100 10 0.560 0.4 2.6
Murata LQH4N220 22 0.560 0.4 2.6
Sumida CD43-8R2 8.2 0.132 1.26 3.2
Sumida CD43-100 10 0.182 1.15 3.2
Sumida CD54-100 10 0.100 1.44 4.5
Sumida CD54-180 18 0.150 1.23 4.5
Sumida CD54-220 22 0.180 1.11 4.5

MAX1674/MAX1675/MAX1676

High-Efficiency, Low-Supply-Current,
Compact, Step-Up DC-DC Converters

12 ______________________________________________________________________________________

TRANSISTOR COUNT: 751

Chip Information

Package Information

Optional External Rectifier

Although not required, a Schottky diode (such as the
MBR0520) connected between LX and OUT allows
lower start-up voltages (Figure 10) and is recommend­ed for single-cell operation. Note that adding this diode
provides no significant efficiency improvement.

PC Board Layout and Grounding

Careful printed circuit layout is important for minimizing
ground bounce and noise. Keep the IC’s GND pin and
the ground leads of the input and output filter capaci­tors less than 0.2in (5mm) apart. In addition, keep all
connections to the FB and LX pins as short as possi­ble. In particular, when using external feedback resis­tors, locate them as close to the FB as possible. To
maximize output power and efficiency and minimize
output ripple voltage, use a ground plane and solder
the IC’s GND directly to the ground plane.

MAX1674
MAX1675
MAX1676

BATT
(MAX1676)

V

IN

SINGLE CELL

LBI

REF

GND

R3

R1

200Ω

R4

R2
100k

22µH

47µF

0.1µF

LX

LBO

FB

SHDN

OUT

LOW-BATTERY
OUTPUT

0.1µF

MBR0520

47µF

CLSEL
(MAX1676)

Figure 10. Adding a Schottky Diode for Single-Cell Operation

10LUMAXB.EPS