FREI MAX1797EUA+ Datasheet

MAX1795/MAX1796/
MAX1797

Low-Supply Current, Step-Up DC-DC Converters

with True Shutdown

General Description

The MAX1795/MAX1796/MAX1797 are high-efficiency,
step-up DC-DC converters intended for small portable
hand-held devices. These devices feature Maxim’s True
Shutdown™ circuitry, which fully disconnects the out­put from the input in shutdown, improves efficiency,
and eliminates costly external components. All three
devices also feature Maxim’s proprietary LX-damping
circuitry for reduced EMI in noise-sensitive applications.
For additional in-system flexibility, a battery monitoring
comparator (LBI/LBO) remains active even when the
DC-DC converter is in shutdown.

The input voltage range is +0.7V to V
can be set from +2V to +5.5V. Startup is guaranteed
from +0.85V. The MAX1795/MAX1796/MAX1797 have a
preset, pin-selectable 5V or 3.3V output. The output can
also be adjusted to other voltages, using two external
resistors. The three devices differ only in their current
limits, allowing optimization of external components for
different loads: The MAX1795, MAX1796, and MAX1797
have current limits of 0.25A, 0.5A, and 1A, respectively.
All devices are packaged in a compact, 8-pin μMAX
package that is only 1.09mm tall and half the size of an
8-pin SO.

OUT

, where V

OUT

Features

● > 95% Efficiency

● True-Shutdown Circuitry

• Output Disconnects from Input in Shutdown

• No External Schottky Diode Needed

● 25μA Quiescent Supply Current

● Low-Noise Antiringing Feature

● LBI/LBO Comparator Enabled in Shutdown

● 2μA Shutdown Current

● 8-Pin μMAX Package

Ordering Information

PART TEMP RANGE PIN-PACKAGE

MAX1795EUA -40°C to +85°C 8 μMAX
MAX1796EUA -40°C to +85°C 8 μMAX
MAX1797EUA -40°C to +85°C 8 μMAX

Applications

● Portable Digital Audio Players

● PDAs/Palmtops

● Wireless Handsets

● Portable Terminals

Pin Conguration Typical Operating Circuit

IN

0.7V TO

TOP VIEW

1

LBI

MAX1795

2

FB

MAX1796

3

LBO

SHDN

True Shutdown is a trademark of Maxim Integrated Products.

MAX1797

4

µMAX

8

BATT

7

OUT

6

LX

5

GND

5.5V

OFF

ON

BATT

LBI

LBO

SHDN

MAX1795
MAX1796
MAX1797

GND

OUT

LX

OUT

FB

19-1798; Rev 0; 12/00

MAX1795/MAX1796/
MAX1797

Low-Supply Current, Step-Up DC-DC Converters

with True Shutdown

Absolute Maximum Ratings

OUT, LX, SHDN, LBI, LBO, BATT to GND ..............-0.3V to +6V

FB ........................................................... -0.3V to (V

ILX, I

Output Short-Circuit Duration .................................................. 5s

Continuous Power Dissipation

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

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.

............................................................................. ±1.5A

OUT

OUT

+ 0.3V)

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

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

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

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

Electrical Characteristics

(V

= +2V, OUT = FB (V

BATT

TA = +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Minimum Input Voltage After startup 0.7 V

Operating Voltage V

Startup Voltage TA = +25°C, RL = 3kΩ 0.85 1.0 V

Startup Voltage Tempco -2.2 mV/°C

Output Voltage V

Adjustable Output Voltage Range 2.0 5.5 V

Steady-State Output Current I

Feedback Set-Point Voltage
(Adjustable Mode)

Feedback Input Current I

Internal NFET, PFET
On-Resistance

LX Switch Current Limit
(NFET only)

LX Leakage Current I

Synchronous Rectier Turn-Off

Current Limit

Damping Switch On-Resistance R

Operating Current into OUT
(Note 2)

= +3.3V), SHDN = LBI = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at

OUT

BATT

OUT

OUT

V

R

DS(ON)

I

LIM

LEAK

DAMP

FB

FB

(Note 1) 1.0 5.5 V

FB = OUT 3.17 3.3 3.43

FB = GND 4.80 5.0 5.20

BATT = +2V,
FB = OUT
(V

= +3.3V)

OUT

BATT = +2V,
FB = GND
(V

= +5.0V)

OUT

V

= +2V to +5.5V 1.20 1.24 1.28 V

OUT

VFB = +1.24V 4 100 nA

V

= +3.3V,

OUT

ILX = 100mA

MAX1795 0.2 0.25 0.35

MAX1797 0.8 1.0 1.25

V

= 0 and +5.5V, V

LX

VFB = +1.4V 25 45 µA

MAX1795 100 180

MAX1796 200 300

MAX1797 400 550

MAX1795 50 120

MAX1796 100 200

MAX1797 250 370

NFET 0.17 0.3

PFET 0.27 0.45

= +5.5V 0.2 µA

OUT

25 mA

100 200 400 Ω

V

mA

Ω

AMAX1796 0.4 0.5 0.625

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2

MAX1795/MAX1796/
MAX1797

Low-Supply Current, Step-Up DC-DC Converters

with True Shutdown

Electrical Characteristics (continued)

(V

= +2V, OUT = FB (V

BATT

TA = +25°C.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Operating Current into BATT VFB = +1.4V, V

Shutdown Current into BATT SHDN = BATT, V

LX Switch MaxImum On-Time t

LX Switch Minimum Off-Time t

LBI Threshold Voltage Falling V

LBI Hysteresis 25 mV

LBI Input Current I

LBO Low Output Voltage

LBO Off-Leakage Current V

SHDN Input Voltage

Shutdown Input Current V

= +3.3V), SHDN = LBI = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at

OUT

= +1V 2 4 µA

LBI

= +1V 2 4 µA

LBI

ON

OFF

LBI

LBI

V

IL

V

IH

VFB = +1V, if current limit not reached 3 4 5 µs

VFB = +1V 0.8 1 1.2 µs

V

= +2V 0.8 0.85 0.90

BATT

V

= LBI 0.875 0.925 0.975

BATT

V

= +0.8V 9 100 nA

LBI

V

= V

= V

= +0.975V,

LBI

= +1.1V,

LBI

0.1

0.1

BATT

sinking 20µA (50Ω typ)

V

BATT

sinking 100µA (25Ω typ)

= +5.5V 1 100 nA

LBO

0.2 x

V

BATT

0.8 x
V

BATT

= 0 and +5.5V 100 nA

SHDN

V

V

V

Electrical Characteristics

(V

= +2V, OUT = FB (V

BATT

PARAMETER SYMBOL CONDITIONS MIN MAX UNITS

Operating Voltage V

Output Voltage V

Adjustable Output Voltage Range 2.0 5.5 V

Steady-State Output Current
(Note 1)

Feedback Set-Point Voltage
(Adjustable Mode)

Feedback Input Current I

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= +3.3V), SHDN = LBI = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 3)

OUT

BATT

Note 1 1.0 5.5 V

FB = OUT 3.13 3.47

OUT

FB = GND 4.75 5.25

MAX1795 100

I

OUT

FB = OUT
(V

= +3.3V)

OUT

FB = GND
(V

= +5.0V)

OUT

MAX1796 200

MAX1797 400

MAX1795 60

MAX1796 125

MAX1797 250

V

FB

FB

V

= +2V to +5.5V 1.19 1.29 V

OUT

VFB = +1.25V 100 nA

Maxim Integrated

V

mA

│

3

MAX1795/MAX1796/

Low-Supply Current, Step-Up DC-DC Converters

MAX1797

Electrical Characteristics (continued)

(V

= +2V, OUT = FB (V

BATT

PARAMETER SYMBOL CONDITIONS MIN MAX UNITS

Internal NFET, PFET
On-Resistance

LX Switch Current Limit
(NFET only)

LX Leakage Current I

Damping Switch On-Resistance R

Operating Current into OUT
(Note 2)

Operating Current into BATT VFB = +1.4V, V

Shutdown Current into BATT SHDN = BATT, V

LX Switch Maximum On-Time t

LX Switch Minimum Off-Time t

LBI Threshold Voltage V

LBI Input Current I

LBO Low Output Voltage

LBO Off-Leakage Current V

SHDN Input Voltage

Shutdown Input Current V

= +3.3V), SHDN = LBI = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 3)

OUT

V

= +3.3V,

R

DS(ON)

OUT

ILX = 100mA

MAX1795 0.19 0.37

I

LIM

MAX1797 0.8 1.32

LEAK

DAMP

VLX = 0 and +5.5V, V

VFB = +1.4V 45 µA

ON

OFF

LBI

LBI

VFB = +1V, if current limit not reached 2.75 5.25 µs

VFB = +1V 0.7 1.3 µs

V

= +2V 0.8 0.90

BATT

V

= LBI 0.875 0.975

BATT

V

= +0.8V 100 nA

LBI

V

= V

BATT

LBI

sinking 20µA (50Ω typ)

V

= V

BATT

LBI

sinking 100µA (25Ω typ)

= +5.5V 100 nA

LBO

V

IL

V

IH

= 0 and +5.5V 100 nA

SHDN

with True Shutdown

NFET 0.3

PFET 0.45

= +5.5V µA

OUT

100 400 Ω

= +1V 4 µA

LBI

= +1V 4 µA

LBI

= +0.975V,

= +1.1V,

0.8 x
V

BATT

0.1

0.1

0.2 x

V

BATT

Ω

AMAX1796 0.35 0.7

V

V

V

Note 1: Operating Voltage: Since the regulator is bootstrapped to the output, once started it will operate down to a 0.7V input.
Note 2: Device is bootstrapped (power to IC comes from OUT). This correlates directly with the actual battery supply current.
Note 3: Specifications to -40°C are guaranteed by design, not production tested.

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EFFICIENCY (%)

MAX1796

EFFICIENCY (%)

EFFICIENCY (%)

MAX1797

EFFICIENCY (%)

EFFICIENCY (%)

EFFICIENCY (%)

EFFICIENCY (%)

MAX1795/MAX1796/
MAX1797

Typical Operating Characteristics

(L = 22μH, CIN = 47μF, C

= 47μF, TA = +25°C, unless otherwise noted.)

OUT

Low-Supply Current, Step-Up DC-DC Converters

with True Shutdown

EFFICIENCY vs. LOAD CURRENT (+5V)

MAX1795

100

V

= +3.6V

BATT

90

80

70

60

50

40

30

20

10

0

V

= +2.4V

BATT

0.1 1 10 100 1000

LOAD CURRENT (mA)

V

BATT

EFFICIENCY vs. LOAD CURRENT (+3.3V)

100

V

= +2.4V

BATT

90

80

V

= +1.2V

70

60

50

40

30

20

10

0

0.1 1 10 100 1000

BATT

LOAD CURRENT (mA)

NO-LOAD BATTERY CURRENT

vs. INPUT BATT VOLTAGE

300

250

200

150

V

= +5V

100

BATTERY CURRENT (µA)

50

0

V

0 1.0 1.5 2.00.5 2.5 3.0 3.5 4.0 4.5 5.0 5.5

OUT

= +3.3V

OUT

BATT VOLTAGE (V)

= +1.2V

100

90

80

MAX1795/96/97 toc01

70

60

50

40

30

20

10

100

MAX1795/96/97 toc04

4.0

3.5

3.0

MAX1795/96/97 toc07

2.5

2.0

1.5

1.0

0.5

EFFICIENCY vs. LOAD CURRENT (+3.3V)

MAX1795

V

= +2.4V

BATT

V

= +1.2V

BATT

0

0.1 1 10 100 1000

LOAD CURRENT (mA)

L = 10µH

EFFICIENCY vs. LOAD CURRENT (+5V)

V

= +3.6V

BATT

90

80

70

60

50

40

30

20

10

0

0.1 1 10 100 1000

LOAD CURRENT (mA)

V

V

BATT

BATT

= +2.4V

= +1.2V

STARTUP VOLTAGE
vs. LOAD CURRENT

V

= +3.3V

OUT

0

0.1 10 1001 1000

LOAD CURRENT (mA)

EFFICIENCY vs. LOAD CURRENT (+5V)

100

V

BATT

90

80

MAX1795/96/97 toc02

70

60

50

40

30

20

10

0

0.1 1 10 100 1000

EFFICIENCY vs. LOAD CURRENT (+3.3V)

100

V

BATT

90

80

MAX1795/96/97 toc05

70

60

50

40

30

20

10

0

0.1 1 10 100 1000

3.0

2.5

MAX1795/96/97 toc08

2.0

1.5

1.0

SHUTDOWN THRESHOLD (V)

0.5

0

0 1.0 1.5 2.00.5 2.5 3.0 3.5 4.0 4.5 5.0 5.5

MAX1796

= +3.6V

V

= +2.4V

BATT

LOAD CURRENT (mA)

V

BATT

= +1.2V

MAX1797

= +2.4V

V

= +1.2V

BATT

LOAD CURRENT (mA)

SHUTDOWN THRESHOLD

vs. INPUT BATT VOLTAGE

BATT VOLTAGE (V)

MAX1795/96/97 toc03

MAX1795/96/97 toc06

MAX1795/96/97 toc09

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LOW-BATTERY INPUT THRESHOLD (V)

MAX1795/96/97 toc10

MAX1795/96/97 toc11

LOW-BATTERY INPUT THRESHOLD (V)

MAX1795

MAX1795/MAX1796/

Low-Supply Current, Step-Up DC-DC Converters

MAX1797

Typical Operating Characteristics (continued)

(L = 22μH, CIN = 47μF, C

= 47μF, TA = +25°C, unless otherwise noted.)

OUT

with True Shutdown

LOW-BATTERY INPUT THRESHOLD

vs. INPUT BATT VOLTAGE

0.950

0.925

0.900

0.875

0.850

0.825

0.800
0 1.0 1.5 2.00.5 2.5 3.0 3.5 4.0 4.5 5.0 5.5

INCREASING V

DECREASING V

BATT VOLTAGE (V)

MAXIMUM OUTPUT CURRENT

vs. BATT INPUT VOLTAGE

500

400

300

V

= +3.3V

OUT

200

LOAD CURRENT (mA)

100

LBI

LBI

MAX1796

V

OUT

= +5.0V

LOW-BATTERY INPUT THRESHOLD

vs. TEMPERATURE

0.950

V

= +3.6V

0.925

0.900

0.875

0.850

0.825

0.800

BATT

INCREASING V

DECREASING V

-40 10-15 35 60 85

TEMPERATURE (°C)

MAX1795/96/97 toc13

LBI

LBI

250

200

150

100

LOAD CURRENT (mA)

50

MAXIMUM OUTPUT CURRENT

vs. BATT INPUT VOLTAGE

1000

800

V

600

400

LOAD CURRENT (mA)

200

MAXIMUM OUTPUT CURRENT

vs. BATT INPUT VOLTAGE

V

= +3.3V

OUT

V

= +5.0V

OUT

0

0 1.5 2.00.5 1.0 2.5 3.0 3.5 4.0 4.5

BATT VOLTAGE (V)

MAX1797

OUT

= +3.3V

V

OUT

= +5.0V

MAX1795/96/97 toc14

MAX1795/96/97 toc12

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0

0 1.5 2.00.5 1.0 2.5 3.0 3.5 4.0 4.5

BATT VOLTAGE (V)

OUT LEAKAGE CURRENT

vs. OUTPUT VOLTAGE

2.0
SHDN = BATT

V

= +5V

OUT

= +2.4V

V

BATT

1.6

1.2

0.8

OUT LEAKAGE CURRENT (A)

0.4

0

0 1.0 1.50.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

OUT BIASED WITH
EXTERNAL VOLTAGE
SOURCE

OUTPUT VOLTAGE (V)

MAX1795/96/97 toc15

0

0 1.5 2.00.5 1.0 2.5 3.0 3.5 4.0 4.5

BATT VOLTAGE (V)

HEAVY-LOAD SWITCHING WAVEFORMS

V
V
I

LOAD

IN
OUT

= +3.6V

= +5.0V

= 400mA

4.00µs/div

MAX1795/96/97 toc16

Maxim Integrated

V

LX

5V/div

I

INDUCTOR

500mA/div

V

OUT

(AC-COUPLED)
100mV/div

│

6

MAX1795/MAX1796/

Low-Supply Current, Step-Up DC-DC Converters

MAX1797

Typical Operating Characteristics (continued)

(L = 22μH, CIN = 47μF, C

= 47μF, TA = +25°C, unless otherwise noted.)

OUT

with True Shutdown

LIGHT-LOAD SWITCHING WAVEFORMS

V

BATT

V

OUT

I

LOAD

= +3.6V

= +5.0V

= 40mA

20µs/div

LOAD-TRANSIENT RESPONSE

MAX1795/96/97 toc17

MAX1795/96/97 toc19

V

LX

5V/div

I

INDUCTOR

500mA/div

V

OUT

(AC-COUPLED)
100mV/div

I

OUT

100mA/div

V

OUT

100mV/div

LINE-TRANSIENT RESPONSE

= +2.7V TO +3V

V

BATT

V

= +5.0V

OUT

NO LOAD

10µs/div

STARTUP-SHUTDOWN WAVEFORMS

MAX1795/96/97 toc18

MAX1795/96/97 toc20

V

BATT

+2.7V TO +3V

V

OUT

(AC-COUPLED)
20mV/div

V

SHDN

5V/div

V

OUT

2V/div

I

INDUCTOR

500mA/div

V

= +2.4V

BATT

V

= +3.3V

OUT

I

= 0 TO 325mA

LOAD

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40µs/div

V
V
I

LOAD

BATT
OUT

= +2.4V
= +5.0V
= 200mA

2ms/div

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7

MAX1795/MAX1796/

Low-Supply Current, Step-Up DC-DC Converters

MAX1797

Pin Description

PIN NAME FUNCTION

1 LBI

2 FB

3 LBO

4 SHDN

5 GND Ground

6 LX Inductor Connection

7 OUT Power Output. OUT provides bootstrap power to the IC.

8 BATT Battery Input and Damping Switch Connection

Low-Battery Comparator Input. Internally set to trip at +0.85V. This function remains operational in
shutdown.

Dual-Mode™ Feedback Input. Connect to GND for preset 5.0V output. Connect to OUT for preset 3.3V
output. Connect a resistive voltage-divider from OUT to GND to adjust the output voltage from 2V to 5.5V.

Low-Battery Comparator Output, Open-Drain Output. LBO is high impedance when V
This function remains operational in shutdown.

Shutdown Input. If SHDN is high, the device is in shutdown mode, OUT is high impedance, and LBI/LBO
are still operational. Connect shutdown to GND for normal operation.

with True Shutdown

< 0.85V.

LBI

Detailed Description

The MAX1795/MAX1796/MAX1797 compact step-up
DC-DC converters start up with voltages as low as

0.85V and operate with an input voltage down to +0.7V.

Consuming only 25μA of quiescent current, these devices

have an internal 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 N-channel MOSFET power switch resistance

is typically 0.17Ω, which minimizes losses. The LX switch

current limits of the MAX1795/MAX1796/MAX1797 are

0.25A, 0.5A, and 1A, respectively.

All three devices offer Maxim’s proprietary True Shutdown
circuitry, which disconnects the output from the input
in shutdown and puts the output in a high impedance
state. These devices also feature Maxim’s proprietary
LX-damping circuitry, which reduces EMI in noise-sensi­tive applications. For additional in-system flexibility, the
LBI/LBO comparator remains active in shutdown. Figure

1 is a typical application circuit.

Control Scheme

A unique minimum-off-time, current-limited control

scheme is the key to the MAX1795/MAX1796/MAX1797s’
low operating current and high efficiency over a wide
load range. The architecture combines the high output
power and efficiency of a pulse-width-modulation (PWM)

device with the ultra-low quiescent current of a traditional

V

IN

1M

SHDN

LBO

V

IN

LBI

*SEE TABLE 1 FOR COMPONENT VALUES.

Figure 1. Typical Application Circuit

BATT

MAX1795
MAX1796
MAX1797

OUT

GND

22µH

LX

C

*

OUT

FB

47µF

V

OUT

= 3.3V

pulse-skipping controller (Figure 2). Switching frequency
depends upon the load current and input voltage, and can
range up to 500kHz. 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).

Dual Mode is a trademark of Maxim Integrated Products.

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MAX1795/MAX1796/
MAX1797

BATT

R1
1M

Low-Supply Current, Step-Up DC-DC Converters

with True Shutdown

OUT

SHDN

LBO

LBI

+

MAX1795
MAX1796
MAX1797

S

Q

_

R

0.85V

S

Q

R

TIMER BLOCK

S

Q

START

R2

FB

R3

TON MAX

FB SELECT

REFERENCE

TOFF

MAX

ERROR
AMPLIFIER

R

CURRENT-LIMIT

ZERO­CROSSING
AMPLIFIER

AMPLIFIER

BODY

DIODE

CONTROL

OUT

BATT

GND

OUT

47µF

BATT

22µH

47F

LX

Figure 2. Functional Diagram

Synchronous Rectication

The internal synchronous rectifier eliminates the need
for an external Schottky diode, reducing cost and board
space. During the cycle off-time, the P-channel MOSFET
turns on and shunts the MOSFET body diode. As a
result, the synchronous rectifier significantly improves
efficiency without the addition of an external component.
Conversion efficiency can be as high as 95%, as shown
in the Typical Operating Characteristics section.

Shutdown

The device enters shutdown when V
reducing supply current to less than 2μA. During shut­down, the synchronous rectifier disconnects the output
from the input, eliminating the DC conduction path
that normally exists with traditional boost converters in
shutdown mode. In shutdown, OUT becomes a high-

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SHDN

is high,

impedance node. The LBI/LBO comparator remains
active in shutdown.

As shown in Figure 1, the MAX1795/MAX1796/MAX1797
can be automatically shut down when the input voltage
drops below a preset threshold by connecting LBO to
SHDN (see the Low-Battery Detection section).

BATT/Damping Switch

The MAX1795/MAX1796/MAX1797 each contain an inter­nal damping switch to minimize ringing at LX. The damp­ing switch connects a resistor across the inductor when
the inductor’s energy is depleted (Figure 3). 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

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MAX1795/MAX1796/
MAX1797

Low-Supply Current, Step-Up DC-DC Converters

with True Shutdown

V

IN

BATT

MAX1795
MAX1796
MAX1797

R1
200Ω

DAMPING
SWITCH

LX

OUT

22µH

V

OUT

47µF

Figure 3. Simplified Diagram of Inductor Damping Switch

V

LX

1V/div

path to quickly dissipate this energy, minimizing the ringing

at LX. Damping LX ringing does not reduce V

OUT

ripple,

but does reduce EMI (Figure 3, Figure 4, and Figure 5).

Setting the Output Voltage

V

can be set to 3.3V or 5.0V by connecting the FB

OUT

pin to GND (5V) or OUT (3.3V). To adjust the output
voltage, connect a resistive voltage-divider from OUT to
FB to GND (Figure 6). Choose a value less than 250kΩ
for R2.

V

IN

47µF

BATT

R3

LBI

MAX1795

R4

MAX1796
MAX1797

GND

OUT

SHDN

LBO

LX

OUTPUT

1M

R1

FB

R2

2V TO 5.5V

47µF

LOW-BATTERY
OUTPUT

2µs/div

Figure 4. LX Ringing for Conventional Step-Up Converter
(without Damping Switch)

V

LX

1V/div

2µs/div

Figure 5. LX Waveform with Damping Switch

Figure 6. Setting an Adjustable Output

Use the following equation to calculate R1:

R1 = R2 [(V

where VFB = +1.245V, and V

OUT/VFB

OUT

) - 1]

can range from +2V to

+5.5V.

Low-Battery Detection

The MAX1795/MAX1796/MAX1797 each contain an on­chip comparator for low-battery detection. If the voltage
at LBI is above 0.85V, LBO (an open-drain output) sinks
current to GND. If the voltage at LBI is below 0.85V, LBO
goes high impedance. The LBI/LBO function remains
active even when the part is in shutdown.

Connect a resistive voltage-divider to LBI from BATT to
GND. The low-battery monitor threshold is set by two
resistors, R3 and R4 (Figure 6). Since the LBI bias current

is typically 2nA, large resistor values (R4 up to 250kΩ)

can be used to minimize loading of the input supply.

Calculate R3 using the following equation:

R3 = R4[(V

/0.85V) - 1]

TRIP

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V I (R L ) V

and

+× + −




MAX1795/MAX1796/

Low-Supply Current, Step-Up DC-DC Converters

MAX1797

V

is the input voltage where the low-battery detector

TRIP

output goes high impedance.

For single-cell applications, LBI may be connected to the
battery. When V

0.925V (see the Typical Operating Characteristics section).

Connect a pullup resistor of 100kΩ or greater from LBO to

OUT for a logic output. LBO is an open-drain output and
can be pulled as high as 6V regardless of the voltage at
OUT. When LBI is below the threshold, the LBO output
is high impedance. If the low-battery comparator is not
used, ground LBI and LBO.

Applications Information

Inductor Selection

An inductor value of 22μH performs well in most appli­cations. The MAX1795/MAX1796/MAX1797 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, but have lower output current capabil­ity. Circuits using larger inductance values exhibit higher
output current capability, but are physically larger for the
same series resistance and current rating.

The inductor’s incremental saturation current rating should
be greater than the peak switch-current limit, which is

0.25A for the MAX1795, 0.5A for the MAX1796, and 1A for
the MAX1797. 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 some sug-
gested components for typical applications.

The inductor’s DC resistance significantly affects efficien­cy. Calculate the maximum output current (I
as follows, using inductor ripple current (I
cycle (D):

I

RIP

D

OUT LIM PFET ESR BATT

=

V I (R L ) V

+− × + −

OUT LIM PFET ESR BATT

=

+− × − +

V I (R R L )

OUT LIM PFET NFET ESR

<1.0V>, the LBI threshold increases to

BATT

RIP

 +

t2











(R L )

L

+

OFF

I

RIP

2

I

RIP

2

PFET ESR

OUT(MAX)

) and duty

)

with True Shutdown



= +




where: I

V

I

R

II

OUT( MAX ) LIM

= Inductor ripple current (A)

RIP

= Output voltage (V)

OUT

= Device current limit (0.25A, 0.5A, or 1A)

LIM

= On-resistance of P-channel MOSFET

PFET

(Ω) (typ 0.27Ω)

L

V

= ESR of Inductor (Ω) (typ 0.095Ω)

ESR

= Input voltage (V)

BATT

L = Inductor value in μH

t

= LX switch’s off-time (μs) (typ 1μs)

OFF

D = Duty cycle

R

= On-resistance of N-channel MOSFET

NFET

(Ω) (typ 0.17Ω)

I

OUT(MAX)

= Maximum output current (A)

Capacitor Selection

Table 1 lists suggested tantalum or polymer capacitor

values for typical applications. The ESR of both input
bypass and output filter capacitors affects efficiency and
output ripple. Output voltage ripple is the product of the
peak inductor current and the output capacitor ESR. High-

frequency output noise can be reduced by connecting a

0.1μF ceramic capacitor in parallel with the output filter

capacitor. See Table 2 for a list of suggested component
suppliers.

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 FB as possible. To maximize output power
and efficiency and minimize output ripple voltage, use a
ground plane and solder the IC’s GND pin directly to the
ground plane.

I

RIP

2

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MAX1795/MAX1796/

Low-Supply Current, Step-Up DC-DC Converters

MAX1797

Table 1. Suggested Components for Typical Applications

with True Shutdown

COMPONENT VALUE

COMPONENT

Sumida CDRH6D28-220, 22µH Sumida CDRH4D28-220, 22µH

Inductor

Coilcraft DS3316P-223, 22µH Coilcraft DS1608C-223, 22µH

Input Capacitor

Output Capacitor

Taiyo Yuden UMK316BI150KH,

(MAX1797,

1A CURRENT LIMIT)

Sanyo POSCAP 6TPA47M,

47µF

AVX TPSD476M016R0150,

47µF

0.1µF

Table 2. Component Suppliers

COMPANY PHONE FA X

AVX USA 803-946-0690 USA 803-626-3123

Coilcraft USA 847-639-6400

Coiltronics USA 561-241-7876 USA 561-241-9339

Murata

Nihon

Sanyo

Sprague USA 603-224-1961 USA 603-224-1430

Sumida

Taiyo
Yuden

USA 814-237-1431
1-800-831-9172

USA 805-867-2555
Japan 81-3-3494­7411

USA 619-661-6835
Japan 81-7-2070­6306

USA 647-956-0666
Japan 81-3-3607­5111

USA 408-573-4150 USA 408-573-4159

USA 847-639-1238­469

USA 814-238-0490

USA 805-867-2556
Japan 81-3-3494­7414

USA 619-661-1055
Japan 81-7-2070­1174

USA 647-956-0702
Japan 81-3-3607­5144

COMPONENT VALUE

(MAX1796,

0.5A CURRENT LIMIT)

Sanyo POSCAP 6TPA47M,

47µF

AVX TPSD226M016R0150,

22µF

Taiyo Yuden UMK316BI150KH,

0.1µF

Chip Information

TRANSISTOR COUNT: 1100

PROCESS: BiCMOS

COMPONENT VALUE

(MAX1795, 0.25A CURRENT LIMIT)

Sumida CR32-220, 22µH

Sumida CR32-100, 10µH

Murata CQH3C100K34, 10µH

Murata CQH4N100K(J)04, 10µH

Coilcraft DS1608C-223, 22µH

Coilcraft DS1608C-103, 10µH

Sanyo POSCAP 6TPA47M, 47µF

AVX TPSD106M016R0150, 10µF

Taiyo Yuden UMK316BI150KH, 0.1µF

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MAX1795/MAX1796/
MAX1797

Package Information

Low-Supply Current, Step-Up DC-DC Converters

with True Shutdown

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.

Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses

are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.

Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.

©

2000 Maxim Integrated Products, Inc.

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