MAX856 Datasheet

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_______________General Description

The MAX856–MAX859 are high-efficiency, CMOS, step-
up, DC-DC switching regulators for small, low input volt-
age or battery-powered systems. The MAX856/MAX858
accept a positive input voltage between 0.8V and V

OUT

and convert it to a higher, pin-selectable output voltage of
3.3V or 5V. The MAX857/MAX859 adjustable versions
accept 0.8V to 6.0V input voltages and generate higher
adjustable output voltages in the 2.7V to 6.0V range.
Typical efficiencies are greater than 85%. Typical quies-
cent supply current is 25µA (1µA in shutdown).

The MAX856–MAX859 combine ultra-low quiescent supply
current and high efficiency to give maximum battery life. An
internal MOSFET power transistor permits high switching
frequencies. This benefit, combined with internally set peak
inductor current limits, permits the use of small, low-cost
inductors. The MAX856/MAX857 have a 500mA peak
inductor current limit. The MAX858/MAX859 have a 125mA
peak inductor current limit.

________________________Applications

3.3V to 5V Step-Up Conversion
Palmtop Computers
Portable Data-Collection Equipment
Personal Data Communicators/Computers
Medical Instrumentation
2-Cell & 3-Cell Battery-Operated Equipment
Glucose Meters

____________________________Features

0.8V to 6.0V Input Supply Voltage

0.8V Typ Start-Up Supply Voltage

85% Efficiency at 100mA

25µA Quiescent Current

1µA Shutdown Mode

125mA and 500mA Switch-Current Limits Permit
Use of Low-Cost Inductors

Up to 500kHz Switching Frequency

±1.5% Reference Tolerance Over Temperature

Low-Battery Detector (LBI/LBO)

8-Pin SO and µMAX Packages

______________Ordering Information

Ordering Information continued at end of data sheet.

*  Dice are tested at T

A

= +25°C only.

Contact factory for availability.

MAX856–MAX859

3.3V/5V or Adjustable-Output, 

Step-Up DC-DC Converters

________________________________________________________________

Maxim Integrated Products

1

1

2

3

4

8

7

6

5

LX

GND

OUT

LBI

LBO

REF

3/5

SHDN

MAX856
MAX858

SO/

µ

MAX

TOP VIEW

1

2

3

4

8

7

6

5

LX

GND

OUT

LBI

LBO

REF

FB

SHDN

MAX857
MAX859

SO/

µ

MAX

__________________Pin Configuration

MAX856

SHDN

3/5

REF

LX

GND

OUT

INPUT

0.8V TO V

OUT

1N5817

OUTPUT

5V AT 100mA

OR

3.3V AT 125mA

LBO

68

µ

F

47

µ

H

LOW-BATTERY
DETECTOR OUTPUT

ON/OFF

3V/5V SELECT

LBI

LOW-BATTERY

DETECTOR

INPUT

__________Typical Operating Circuit

Call toll free 1-800-998-8800 for free samples or literature.

19-0211; Rev 3; 7/95

PART

TEMP. RANGE

PIN-PACKAGE

MAX856

CSA

0°C to +70°C

8 SO

MAX856CUA

0°C to +70°C

8 µMAX

MAX856C/D

0°C to +70°C

Dice*

MAX856ESA

-40°C to +85°C

8 SO

MAX856MJA

-55°C to +125°C

8 CERDIP

MAX857

CSA

0°C to +70°C

8 SO

MAX857CUA

0°C to +70°C

8 µMAX

MAX857C/D

0°C to +70°C

Dice*

MAX857ESA

-40°C to +85°C

8 SO

MAX857MJA

-55°C to +125°C

8 CERDIP

EVALUATION KIT MANUAL

FOLLOWS DATA SHEET

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MAX856–MAX859

3.3V/5V or Adjustable-Output, 
Step-Up DC-DC Converters

2

_______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(Circuits of Figure 2, V

IN

= 2.5V, I

LOAD

= 0mA, T

A

= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at T

A

= +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, +7V
Switch Voltage (LX to GND)  .......................................-0.3V, +7V
S

H

D

N

, LBO to GND ....................................................-0.3V, +7V

LBI, REF, 3/

5

, FB to GND .........................-0.3V, (V

OUT

+ 0.3V)

Reference Current (I

REF

) ..................................................2.5mA

Continuous Power Dissipation (T

A

= +70°C)

SO (derate 5.88mW/°C above +70°C)  .........................471mW
µMAX (derate 4.1mW/°C above +70°C)  ......................330mW
CERDIP (derate 8.00mW/°C above +70°C)  .................640mW

Reverse Battery Current (T

A

+45°C, Note 1) .................750mA

Operating Temperature Ranges

MAX85_C_ _  ......................................................0°C to +70°C
MAX85_E_ _ ....................................................-40°C to +85°C
MAX85_MJA  .................................................-55°C to +125°C

Junction Temperature  .....................................................+150°C
Storage Temperature Range  ............................-65°C to +160°C
Lead Temperature (soldering, 10sec)  ............................+300°C

Note 1:

Reverse battery current is measured from the 

Typical Operating Circuit’s battery input terminal to GND when the battery is 

connected backwards. A reverse current of 750mA will not exceed the SO or CERDIP package dissipation limits but, if left
for an extended time (more than ten minutes), may degrade performance.

LBO = 5V

I

SINK

= 2mA

With falling edge

3/

5

= 3V, -20µA 

REF load 

250µA, C

REF

= 0.22µF

No REF load

MAX858/MAX859

I

LOAD

= 0mA, 3/

5

= 3V, LBI = 1.5V, V

OUT

= 3.47V,

(FB = 1.5V, MAX857/MAX859 only)

MAX856/MAX857

S

H

D

N

= 0V, 3/

5

= 3V, LBI = 1.5V, V

OUT

= 3.47V,

(FB = 1.5V, MAX857/MAX859 only)

2V 

V

IN

3V

I

LOAD

= 0mA

Output set for 3.3V, measured at V

IN

in Figure 2, R3 omitted.

CONDITIONS

µA

1

LBO Output Leakage Current

V

0.4

LBO Output Voltage Low

mV

25

LBI Input Hysteresis

V

1.22

1.25

1.28

LBI Input Threshold

%

0.8

2.0

Reference-Voltage Regulation

V

1.23

1.25

1.27

Reference Voltage

mA

125

500

µA

1

5

Shutdown Quiescent Current
(Note 2)

1

µA

60

No Load Battery Current

4.80

5.0

5.20

3.17

3.3

3.43

4.80

5.0

5.20

µA

25

60

Quiescent Supply Current in
3.3V Mode (Note 2)

V

0.8

Minimum Operating Voltage

4.80

5.0

5.20

3.17

3.3

3.43

V

4.80

5.0

5.20

Output Voltage

V

0.8

1.8

Minimum Start-Up 
Supply Voltage

UNITS

MIN

TYP

MAX

PARAMETER

Peak Inductor Current Limit

MAX856, 3/

5

= 0V, 0mA 

I

LOAD

100mA

MAX856, 3/

5

= 3V, 0mA 

I

LOAD

150mA

MAX857, V

OUT

= 5V, 0mA 

I

LOAD

100mA

MAX858, 3/

5

= 0V, 0mA 

I

LOAD

25mA

MAX858, 3/

5

= 3V, 0mA 

I

LOAD

35mA

MAX859, V

OUT

= 5V, 0mA 

I

LOAD

25mA

MAX85_C

MAX85_E/M

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MAX856–MAX859

3.3V/5V or Adjustable-Output, 

Step-Up DC-DC Converters

_______________________________________________________________________________________

3

100

20

10

0

0.01

0.001

0.1

10

1

100

1000

MAX858/MAX859

EFFICIENCY vs. OUTPUT CURRENT

V

OUT

 = 3.3V

40

30

50

MAX856-01

LOAD CURRENT (mA)

EFFICIENCY (%)

60

70

80

90

V

IN

 = 2.0V

V

IN

 = 2.5V

V

IN

 = 1.5V

100

20

10

0

0.01

0.001

0.1

10

1

100

1000

MAX858/MAX859

EFFICIENCY vs. OUTPUT CURRENT

V

OUT

 = 5V

40

30

50

MAX856-02

LOAD CURRENT (mA)

EFFICIENCY (%)

60

70

80

90

V

IN

 = 2.5V

V

IN

 = 3.3V

V

IN

 = 1.5V

100

20

10

0

0.01

0.001

0.1

10

1

100

1000

MAX856/MAX857

EFFICIENCY vs. OUTPUT CURRENT

V

OUT

 = 5V

40

30

50

MAX856-03

LOAD CURRENT (mA)

EFFICIENCY (%)

60

70

80

90

V

IN

 = 2.0V

V

IN

 = 3.3V

V

IN

 = 1.5V

100

20

10

0

0.01

0.001

0.1

10

1

100

1000

MAX856/MAX857

EFFICIENCY vs. OUTPUT CURRENT

V

OUT

 = 3.3V

40

30

50

MAX856-04

LOAD CURRENT (mA)

EFFICIENCY (%)

60

70

80

90

V

IN

 = 2.0V

V

IN

 = 2.5V

V

IN

 = 1.5V

__________________________________________Typical Operating Characteristics

(Circuits of Figure 2, T

A

= +25°C, unless otherwise noted.)

ELECTRICAL CHARACTERISTICS (continued)

(Circuits of Figure 2, V

IN

= 2.5V, I

LOAD

= 0mA, T

A

= T

MIN

to T

MAX

, unless otherwise noted. Typical values are at T

A

= +25°C.)

Note 2:

Supply current from the 3.3V output is measured with an ammeter between the 3.3V output and OUT pin. This current 
correlates directly with actual battery supply current, but is reduced in value according to the step-up ratio and efficiency.
V

OUT

= 3.47V to keep the internal switch open when measuring the current into the device.

Note 3:

Minimum value is production tested. Maximum value is guaranteed by design and is not production tested.

S

H

D

N

, 3/

5

Input Voltage Low

0.4

V

S

H

D

N

, 3/

5

Input Voltage High

1.6

V

S

H

D

N

, 3/

5

, FB, LBI Input Current

LBI = 1.5V, FB = 1.5V, 

S

H

D

N

= 0V or 3V, 3/

5

= 0V or 3V

±100

nA

FB Voltage

MAX857/MAX859

1.22

1.25

1.28

V

Output Voltage Range

MAX857/MAX859, I

LOAD

= 0mA (Note 3)

2.7

6.0

V

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MAX856–MAX859

3.3V/5V or Adjustable-Output, 
Step-Up DC-DC Converters

4

_______________________________________________________________________________________

_____________________________Typical Operating Characteristics (continued)

(Circuits of Figure 2, T

A

= +25°C, unless otherwise noted.)

0.75

0.1

10

MAX856/MAX857

MINIMUM START-UP INPUT VOLTAGE

vs. LOAD CURRENT

MAX856-06

LOAD CURRENT (mA)

START-UP INPUT VOLTAGE (V)

0.90

1.10

0.80

1.00

1

100

1.15

1.05

0.95

0.85

V

OUT

 = 3.3V

V

OUT

 = 5V

0.1

10

MAX858/MAX859

MINIMUM START-UP INPUT VOLTAGE

vs. LOAD CURRENT

MAX856-07

LOAD CURRENT (mA)

START-UP INPUT VOLTAGE (V)

0.9

1.3

1.1

1

100

1.4

1.2

1.0

0.8

V

OUT

 = 5V

0.8

2.0

SHUTDOWN CURRENT

vs. INPUT VOLTAGE

0.7

MAX856-11

SHUTDOWN CURRENT (

µ

A)

0.5

1.5

0.6

2.5

3.0

0.4

0.3

0.2

0.1

0

3.5

4.0

INPUT VOLTAGE (V)

T

A

 = +85°C

T

A

 = +25°C

T

A

 = -40°C

0.9

1.0

80

2.0

MAX858/MAX859

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE

70

MAX856-12

LOAD CURRENT (mA)

50

1.5

60

2.5

3.0

40

30

20

10

0

3.5

4.0

INPUT VOLTAGE (V)

90

100

1.0

V

OUT

 = 5.0V

V

OUT

 = 3.3V

400

1.0

MAX856/MAX857

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE

350

MAX856-13

LOAD CURRENT (mA)

250

300

2.0

1.5

2.5

200

150

100

50

0

3.0

3.5

4.0

INPUT VOLTAGE (V)

V

OUT

 = 5.0V

V

OUT

 = 3.3V

1.6

2.0

QUIESCENT CURRENT

vs. INPUT VOLTAGE

1.4

MAX856-10

QUIESCENT CURRENT (mA)

1.0

1.5

1.2

2.5

3.0

0.8

0.6

0.4

0.2

0

3.5

4.0

INPUT VOLTAGE (V)

SEE NOTE 2
IN THE ELECTRICAL
CHARACTERISTICS

T

A

 = +85°C

T

A

 = -40°C

1.6

2.0

MAX858/MAX859

NO LOAD BATTERY CURRENT

vs. INPUT VOLTAGE

1.4

MAX856-09

QUIESCENT CURRENT (mA)

1.0

1.5

1.2

2.5

3.0

0.8

0.6

0.4

0.2

0

3.5

4.0

INPUT VOLTAGE (V)

INCLUDES ALL EXTERNAL
COMPONENT LEAKAGES.
CAPACITOR LEAKAGE
DOMINATES AT T

A

 = +85°C.

CAPS ARE SPRAGUE 595D

T

= +85°C

T

= +25°C

T

= -40°C

400

2.0

MAX856/MAX857

NO LOAD BATTERY CURRENT

vs. INPUT VOLTAGE

350

MAX856-08

QUIESCENT CURRENT (

µ

A)

250

1.5

300

2.5

3.0

200

150

100

50

0

3.5

4.0

INPUT VOLTAGE (V)

T

A

 = +85°C

T

A

 = +25°C

T

A

 = -40°C

INCLUDES ALL EXTERNAL
COMPONENT LEAKAGES.
CAPACITOR LEAKAGE
DOMINATES AT T

A

 = +85°C.

CAPS ARE SPRAGUE 595 D

5

0

REFERENCE VOLTAGE vs. CURRENT

 

6

10

MAX856-05

REFERENCE LOAD CURRENT (

µ

A)

V

REF

 LOAD REGULATION (mV)

8

7

100

200

9

50

150

250

4

3

2

1

0

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MAX856–MAX859

3.3V/5V or Adjustable-Output, 

Step-Up DC-DC Converters

_______________________________________________________________________________________

5

MAX856/MAX857

 LINE-TRANSIENT RESPONSE (5V MODE)

2ms/div

V

OUT

50mV/div

V

IN

3V

2V

MAX856/MAX857

 LOAD-TRANSIENT RESPONSE (5V MODE)

50

µ

s/div

V

OUT

50mV/div

0mA to 100mA

I

LOAD

V

IN

 = 2.5V

MAX858/MAX859 LOAD-TRANSIENT RESPONSE

2ms/div

V

OUT

50mV/div

0mA to 25mA

I

LOAD

0

25

V

IN

 = 2.5V

MAX859 LINE-TRANSIENT RESPONSE

1ms/div

V

OUT

50mV/div

1V/div

V

IN

3V

2V

MAX858/MAX859 START-UP DELAY (5V MODE)

5ms/div

V

OUT

2V/div

5V/div

V

SHDN

 V

IN

 = 2.5V, I

LOAD

 = 25mA

MAX856 START-UP DELAY (5V MODE)

5ms/div

 

V

OUT

2V/div

5V/div

V

SHDN

V

IN

 = 2.5V, I

LOAD

 = 100mA

_____________________________Typical Operating Characteristics (continued)

(Circuits of Figure 2, T

A

= +25°C, unless otherwise noted.)

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MAX856–MAX859

3.3V/5V or Adjustable-Output, 
Step-Up DC-DC Converters

6

_______________________________________________________________________________________

______________________________________________________________Pin Description

N-Channel Power-MOSFET Drain

8

8

Low-Battery Output. An open-drain N-channel MOSFET sinks current when the voltage at
LBI drops below 1.25V.

4

4

Low-Battery Input. When the voltage on LBI drops below 1.25V, LBO sinks current. 
If not used, connect to V

IN

.

5

5

Connect OUT to the regulator output. OUT provides bootstrap power to the IC.

6

6

Power Ground. Must be low impedance; solder directly to ground plane.

7

7

1.25V Reference Voltage Output. Bypass with 0.22µF to GND (0.1µF if there is no external
reference load). Maximum load capability is 250µA source, 20µA sink.

3

3

Feedback Input for adjustable-output operation. Connect to an external resistor voltage
divider between OUT and GND.

2

Selects the output voltage; connect to GND for 5V output, and to OUT for 3.3V 
output.

2

Shutdown Input. When low, the entire circuit is off and V

OUT

= V

IN

- V

D,

where V

D

is the

forward voltage drop of the external Schottky rectifier.

1

1

FUNCTION

PIN

LX

LBO

LBI

OUT

GND

REF

FB

3/

5

S

H

D

N

NAME

MAX856
MAX858

MAX857
MAX859

_______________Detailed Description

Operating Principle

The MAX856–MAX859 combine a switch-mode regula-
tor, N-channel power MOSFET, precision voltage refer-
ence, and power-fail detector in a single monolithic
device. The MOSFET is a “sense-FET” type for best
efficiency, and has a very low gate threshold voltage to
ensure start-up with low battery voltages (0.8V typ).

PFM Control Scheme

A unique minimum-off-time, current-limited pulse-fre-
quency modulation (PFM) control scheme is a key fea-
ture of the MAX856 series (Figure 1). 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 pulse-skipper.
There is no oscillator; at heavy loads, switching is
accomplished through a constant-peak-current limit in
the switch, which allows the inductor current to vary
between this peak limit and some lesser value. At light
loads, switching frequency is governed by a pair of
one-shots, which set a minimum off-time (1µs) and a
maximum on-time (4µs). The switching frequency
depends upon the load and the input voltage, and can
range up to 500kHz.

The peak switch current of the internal MOSFET power
switch is fixed at 500mA ±100mA (MAX856/MAX857)
or 125mA ±25mA (MAX858/MAX859). The switch’s on-
resistance is typically 1

(MAX856/MAX857) or 4

(MAX858/MAX859), resulting in a switch voltage drop
(V

SW

) of about 500mV under high output loads. The

value of V

SW

will decrease with light current loads. 

Conventional PWM converters generate constant-fre-
quency switching noise, whereas the unique architec-
ture of the MAX856–MAX859 produces variable-fre-
quency switching noise. However, unlike conventional
pulse-skippers (where noise amplitude varies with input
voltage), noise in the MAX856 series does not exceed
the switch current limit times the filter-capacitor equiva-
lent series resistance (ESR).

Voltage Reference

The precision voltage reference is suitable for driving
external loads, such as an analog-to-digital converter.
The voltage-reference output changes less than ±2%
when sourcing up to 250µA and sinking up to 20µA. If
the reference drives an external load, bypass it with
0.22µF to GND. If the reference is unloaded, bypass it
with at least 0.1µF.

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MAX856–MAX859

3.3V/5V or Adjustable-Output, 

Step-Up DC-DC Converters

_______________________________________________________________________________________

7

MAX856–MAX859

SHDN

3/5*

LBO

LBI

N

LBI COMPARATOR

ERROR COMPARATOR

CURRENT-LIMIT

 COMPARATOR

ONE-SHOT

TRIG

Q

Q

ONE-SHOT

TRIG

S

Q

R

F/F

MINIMUM

OFF-TIME

ONE-SHOT

V

IN

LX

N

GND

OUT

V

OUT

**

FB**

**

*

*

REF

REFERENCE

MAXIMUM

ON-TIME

ONE-SHOT

*MAX856/MAX858 ONLY
**MAX857/MAX859 ONLY

Figure 1.  Block Diagram

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MAX856–MAX859

3.3V/5V or Adjustable-Output, 
Step-Up DC-DC Converters

8

_______________________________________________________________________________________

Logic Inputs and Outputs

The 3/5 input is internally diode clamped

to GND

and

OUT, and should not be connected to signals outside
this range. The SHDN input and LBO output (open-
drain) are not clamped to V+ and can be pulled as high
as 7V regardless of the voltage at OUT

Do not leave

control inputs (3/5, LBI, or SHDN) floating.

__________________Design Procedure

Output Voltage Selection

For the MAX856/MAX858,you can select a 3.3V or 5V
output voltage under logic control, or by tying 3/

5 to

GND or OUT. Efficiency is typically better than 80%
over a 2mA to 100mA (MAX856/MAX857) load range.
The device is internally bootstrapped, with power
derived from the output voltage (via OUT). When the
output is in 5V mode, the higher internal supply voltage
results in lower switch-transistor on-resistance, slightly
greater output power, and higher efficiency.
Bootstrapping allows the battery voltage to sag to 0.8V
once the system is started. Therefore, the battery volt-
age ranges from (V

OUT

+ V

D

) to 0.8V (where V

D

is the

forward drop of the Schottky rectifier). If the battery volt-
age exceeds the programmed output voltage, the out-

put will follow the battery voltage. This is acceptable in
many systems; however, the input or output voltage
must not be forced above 7V.

The MAX857/MAX859’s output voltage is set by two
resistors, R1 and R2 (Figure 2b), which form a voltage
divider between the output and FB. Use the following
equation to determine the output voltage:

R1 + R2

V

OUT

= V

REF

( _________ )

R2

where V

REF

= 1.25V.

To simplify resistor selection:

V

OUT

R1 = R2 ( _______ - 1)

V

REF

Since the input bias current at FB has a maximum value
of 100nA, large values (10k

to 300k

) can be used

for R1 and R2 with no significant accuracy loss. For 1%
error, the current through R1 should be at least 100
times FB’s bias current.

C1*

L1

V

IN

D1

1N5817

C2*

R1

R2

LX

OUT

FB

LBO

LBI

REF

SHDN

GND

R3

R4

C3

0.1

µ

F

V

OUT

5

1

3

8

6

2

4

7

MAX857/MAX859

*C1 = C2 = 68

µ

F FOR MAX857

47

µ

H

C1 = C2 = 22

µ

F FOR MAX859

C1*

L1

V

IN

D1

1N5817

C2*

R1

LX

OUT

3/5

LBO

LBI

REF

SHDN

GND

R3

R4

C3

0.1

µ

F

V

OUT

5

1

3

8

6

2

4

7

MAX856/MAX858

*C1 = C2 = 68

µ

F FOR MAX856

OUTPUT
SELECT

47

µ

H

C1 = C2 = 22

µ

F FOR MAX858

Figure 2b.  Standard Application Circuit—Adjustable Output
Voltage

Figure 2a.  Standard Application Circuit—Preset Output
Voltage

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MAX856–MAX859

3.3V/5V or Adjustable-Output, 

Step-Up DC-DC Converters

_______________________________________________________________________________________

9

Low-Battery Detection

The MAX856 series contains an on-chip comparator for
low-battery detection. If the voltage at LBI falls below
the regulator’s internal reference voltage (1.25V), LBO
(an open-drain output) sinks current to GND. The low-
battery monitor’s threshold is set by two resistors, R3
and R4 (Figure 2). Set the threshold voltage using the
following equation:

VLBI

R3 = R4 ( ______ - 1)

VREF

where V

LBI

is the desired threshold of the low-battery

detector and V

REF

is the internal 1.25V reference.

Since the LBI current is less than 100nA, large resistor
values (typically 10k

to 300k

) can be used for R3

and R4 to minimize loading of the input supply. 

When the voltage at LBI is below the internal threshold,
LBO sinks current to GND. Connect a pull-up resistor of
10k

or more from LBO to OUT when driving CMOS

circuits. When LBI is above the threshold, the LBO out-
put is off. If the low-battery comparator is not used,
connect LBI to V

IN

and leave LBO open.

Inductor Selection

An inductor value of 47µH performs well in most
MAX856–MAX859 applications. However, the inductance
value is not critical, and the MAX856–MAX859 will work
with inductors in the 10µH to 100µH 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 dimen-
sions for a given series resistance.

The inductor’s incremental saturation current rating
should be greater than the peak switch-current limit,
which is 500mA for the MAX856/MAX857, and 125mA
for the MAX858/MAX859. However, it is generally
acceptable to bias the inductor into saturation by as
much as 20%, although this will slightly reduce
efficiency.

The inductor’s DC resistance significantly affects effi-
ciency. See the Efficiency vs. Load Current for Various
Inductors graph in the 

Typical Operating Characteristics.

See Tables 1 and 2 for a list of suggested inductor
suppliers. 

Capacitor Selection

A 68µF, 10V, 0.85

, surface-mount tantalum (SMT) 

output filter capacitor typically provides 50mV output
ripple when stepping up from 2V to 5V at 100mA
(MAX856/ MAX857). 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 47µF range are recommended for
the MAX858/MAX859.

The equivalent series resistance (ESR) of both bypass
and filter capacitors affects efficiency and output rip-
ple. The output voltage ripple is the product of the peak
inductor current and the output capacitor’s 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) and AVX (TPS series). Sanyo
OS-CON organic-semiconductor through-hole capaci-
tors also exhibit very low ESR, and are especially useful
for operation at cold temperatures. See Table 1 for a list
of suggested capacitor suppliers.

Rectifier Diode

For optimum performance, a switching Schottky diode
(such as the 1N5817) is recommended. Refer to Table
1 for a list of component suppliers. For low output
power applications, a PN-junction switching diode
(such as the 1N4148) will also work well, although its
greater forward voltage drop will reduce efficiency. 

PC Layout and Grounding

The MAX856 series’ high-frequency operation makes
PC layout important for minimizing ground bounce and
noise. Keep the IC’s GND pin and the ground leads of
C1 and C2 (Figure 1) less than 0.2in (5mm) apart. Also
keep all connections to the FB and LX pins as short as
possible. To maximize output power and efficiency and
minimize output ripple voltage, use a ground plane and
solder the IC’s GND (pin 7) directly to the ground
plane.

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MAX856–MAX859

3.3V/5V or Adjustable-Output, 
Step-Up DC-DC Converters

10

______________________________________________________________________________________

Table 1.  Component Suppliers

COMPANY

PHONE

FAX

AVX

USA:

(207) 282-5111

(207) 283-1941

Coiltronics

USA:

(407) 241-7876

(407) 241-9339

Matsuo

USA:

(714) 969-2491

(714) 960-6492

Motorola

USA:

(408) 749-0510

(800) 521-6274

Murata-Erie

USA:

(800) 831-9172

(404) 684-1541

Nichicon

USA:

(708) 843-7500

(708) 843-2798

Renco

USA:

(619) 661-6835

(516) 586-5562

Sanyo

(619) 661-1055

Japan: 81-7-2070-6306

81-7-2070-1174

Sumida

USA:

(708) 956-0666

(708) 956-0702

Japan: 81-3-3607-5111

81-3-3607-5144

United Chemi-Con

USA:

(714) 255-9500

(714) 255-9400

USA:

(516) 586-5566

CoilCraft

USA:

(708) 639-6400

(708) 639-1469

Nihon

USA:

(805) 867-2555

(805) 867-2556

Japan: 81-3-3494-7411

81-3-3494-7414

TDK

USA:

(708) 803-6100

(708) 803-6294

Japan: 03-3278-5111

03-3278-5358

RECTIFIERS

Motorola
1N5817

Maxim
MAXC001
150µF, low-ESR
electrolytic

Nichicon
PL series
low-ESR
electrolytic

United Chemi-Con
LXF series

Renco
RL 1284-22

CoilCraft
PCH-27-223

Low-Cost
Through Hole

Sanyo
OS-CON series
low-ESR organic
semiconductor

Sumida
RCH654-220

Miniature
Through Hole

Motorola MBR 0530
Nihon EC15QS02L

Matsuo 267 series
Sprague 595D series
AVX TPS series

See Table 2

Surface Mount

CAPACITORS

INDUCTORS

PRODUCTION

METHOD

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MAX856–MAX859

3.3V/5V or Adjustable-Output, 

Step-Up DC-DC Converters

______________________________________________________________________________________

11

__Ordering Information (continued)

___________________Chip Topography

TRANSISTOR COUNT: 357;

SUBSTRATE CONNECTED TO OUT.

8 CERDIP

-55°C to +125°C

MAX859MJA

8 SO

-40°C to +85°C

MAX859ESA

Dice*

0°C to +70°C

MAX859C/D

8 µMAX

0°C to +70°C

MAX859CUA

8 SO

0°C to +70°C

MAX859

CSA

8 CERDIP

-55°C to +125°C

MAX858MJA

8 SO

-40°C to +85°C

MAX858ESA

Dice*

0°C to +70°C

MAX858C/D

8 µMAX

0°C to +70°C

MAX858CUA

8 SO

0°C to +70°C

MAX858

CSA

PIN-PACKAGE

TEMP. RANGE

PART

GND

LBI

OUT

 3/5 OR FB*

 REF

LX

0.084"

(2.1336mm)

0.058"

(1.4732mm)

SHDN

 LBO

*3/5 FOR MAX856/MAX858; FB FOR MAX857/MAX859.

*  Dice are tested at T

A

= +25°C only.

Contact factory for availability.

Table 2.  Surface-Mount Inductor Information

MANUFACTURER PART

INDUCTANCE

(

m

H)

RESISTANCE

(

W

)

RATED CURRENT

(A)

HEIGHT

(mm)

Sumida CDR105B-470

47

0.14

1.0

5.0

Sumida CDR74B-470

47

0.27

0.8

4.5

Sumida CD43-470

47

0.85

0.540

3.2

Sumida CD43-220

22

0.38

0.760

3.2

Murata-Erie LQH4N220

22

0.94

0.320

2.6

Murata-Erie LQH4N470

47

1.5

0.220

2.6

Murata-Erie LQH1N220

22

3.1

0.85

1.8

TDK NLC322522T-220K

22

1.15

0.210

2.2

TDK NLC322522T-470K

47

2.25

0.150

2.2

Coiltronics CTX20-1

20

0.175

1.15

4.2

Coilcraft DT1608-223

22

0.16

0.500

3.2

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MAX856–MAX859

3.3V/5V or Adjustable-Output, 
Step-Up DC-DC Converters

12

______________________________________________________________________________________

________________________________________________________Package Information

DIM

A

A1

A2

A3

B

B1

C

D1

E

E1

e

eA

eB

L

MIN

0.015

0.125

0.055

0.016

0.045

0.008

0.005

0.300

0.240

0.100

0.300

0.115

MAX

0.200

0.175

0.080

0.022

0.065

0.012

0.080

0.325

0.310

0.400

0.150

MIN

0.38

3.18

1.40

0.41

1.14

0.20

0.13

7.62

6.10

2.54

7.62

2.92

MAX

5.08

4.45

2.03

0.56

1.65

0.30

2.03

8.26

7.87

10.16

3.81

INCHES

MILLIMETERS

Plastic DIP

PLASTIC

DUAL-IN-LINE

PACKAGE

(0.300 in.)

DIM

D

D

D

D

D

D

MIN

0.348

0.735

0.745

0.885

1.015

1.14

MAX

0.390

0.765

0.765

0.915

1.045

1.265

MIN

8.84

18.67

18.92

22.48

25.78

28.96

MAX

9.91

19.43

19.43

23.24

26.54

32.13

INCHES

MILLIMETERS

PINS

8

14

16

18

20

24

C

A

A2

E1

D

E

eA

eB

A3

B1

B

0° - 15°

A1

L

D1

e

L

α

C

A1

B

DIM

A

A1

B

C

D

E

e

H

L

α

MIN

0.036

0.004

0.010

0.005

0.116

0.116

0.188

0.016

MAX

0.044

0.008

0.014

0.007

0.120

0.120

0.198

0.026

MIN

0.91

0.10

0.25

0.13

2.95

2.95

4.78

0.41

MAX

1.11

0.20

0.36

0.18

3.05

3.05

5.03

0.66

INCHES

MILLIMETERS

8-PIN 

µ

MAX

MICROMAX SMALL OUTLINE

PACKAGE

0.65

0.0256

A

e

E

H

D

0.101mm
0.004 in

Maker
Maxim Integrated
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