Rainbow Electronics MAX1672 User Manual

________________General Description

The MAX1672 integrates a step-up DC-DC converter with a
linear regulator to provide step-up/down voltage conver­sion. This device provides a constant output voltage for
inputs that vary above and below the output voltage. It has
a 1.8V to 11V input range and a preset 3.3V or 5V output.
The output can also be set from 1.25V to 5.5V using two
resistors. Typical efficiency is 85%.

The MAX1672’s step-up/linear-regulator configuration per­mits the use of a single, physically smaller inductor than
can be used with competing SEPIC and flyback configura­tions. Switch current is also selectable, permitting the use
of smaller inductors in low-current applications. The linear
regulator also acts as a filter to reduce output ripple voltage.

The MAX1672 has a low 85µA quiescent supply current, which
is further reduced to 0.1µA in logic-controlled shutdown. The
output voltage is disconnected from the input in shutdown.
The MAX1672 also has a PGI/PGO low-battery detector.

The MAX1672 comes in a 16-pin QSOP package (same size
as a standard 8-pin SO). For a larger device that delivers more
output current, refer to the MAX710/MAX711. The preassem­bled MAX1672 evaluation kit is available to speed designs.

________________________Applications

Single-Cell, Lithium-Powered 2-Cell to 4-Cell AA Alkaline
Portable Devices Hand-Held Equipment

3.3V and Other Low-Voltage Battery-Powered Devices
Systems with AC Input Adapters

Digital Cameras

____________________________Features

♦ Step-Up/Down Voltage Conversion
♦ 1.8V to 11V Input Range
♦ 3.3V/5V or Adjustable Output Voltage Range
♦ Output Current:

300mA at 5V (VIN≥ 2.5V)
150mA at 5V (VIN≥ 1.8V)

♦ Smaller Inductor than SEPIC and Flybacks
♦ Load Disconnects from Input in Shutdown
♦ Supply Current from Battery:

85µA (No-Load)

0.1µA (Shutdown)

♦ PGI/PGO Low-Battery Comparator
♦ 16-Pin QSOP Package

(same footprint as 8-pin SO)

♦ No External FETs Required
♦ Thermal and Short-Circuit Protection

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone].
For small orders, phone [phone] ext. 3468.

MAX1672

Step-Up/Down DC-DC Converter

in QSOP Package

________________________________________________________________

Maxim Integrated Products

1

19-1307; Rev 0a; 11/97

EVALUATION KIT

AVAILABLE

______________Ordering Information

*

Dice are tested at TA= +25°C.

16
15
14
13
12
11
10

9

1
2
3
4
5
6
7
8

LX LX

PGND
GND
REF
IN
PS
FB
OUT

TOP VIEW

MAX1672

QSOP

PGND

ONA

ILIM

PGO

PGI

3/5

ONB

__________________Pin Configuration

MAX1672

IN

ONA

PGI

ONB

OFF

ON

PGND GND

PS

3.3V/5V
OUTPUT

INPUT

1.8V TO 11V

LOW-BATTERY
DETECTOR
OUTPUT

OUT

PG0

FB

REF

LX

OFF

3/5
ILIM

5V

0.8A

ON

3.3V

0.5A

__________Typical Operating Circuit

PART

MAX1672C/D
MAX1672EEE -40°C to +85°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

Dice*
16 QSOP

MAX1672

Step-Up/Down DC-DC Converter
in QSOP Package

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VPS= 6V, C

REF

= 0.1µF, C

OUT

= 4.7µF, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)

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.

IN, PS, LX, OUT, PGO to GND ......................... -0.3V to +11.5V

ILIM, ONA, ONB, FB, 3/5,

REF, PGI to GND......................................-0.3V to (V

PS

+ 0.3V)

PGND to GND .......................................................-0.3V to +0.3V

OUT Short Circuit to GND..........................................Continuous

Output Current..................................................................350mA

Continuous Power Dissipation (T

A

= +70°C)

16-Pin QSOP (derate above +70°C by 8.3mW/°C).......667mW

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

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

Storage Temperature Range ........................... -65°C to +160°C

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

VPS= 5.5V

V

OUT

= 0V, ONA = GND, ONB = PS

VPS= 2.7V, I

OUT

= 50mA

VPS= 5.5V, I

OUT

= 50mA

ILIM = GND

VLX= 11V, ONA = GND, ONB = PS

VPS= 2.7V, ILX= 50mA

I

REF

= 0mA

VPS= 5.5V, ILX= 50mA

VIN= GND to 11V

ONA = GND, ONB = PS, current measured into PS pin

ONA = PS or ONB = GND, current measured into PS pin,
I

OUT

= 0mA

VIN= 2V, 3/5 = GND, FB = GND, I

OUT

= 10mA to 150mA

VFB= 1.3V

VIN= 3V to 5V, 3/5 = GND, I

OUT

= 100mA

Hysteresis = 15mV typical

CONDITIONS

A0.35 0.7 1.4Output PFET Current Limit

µA0.1 1Output PFET Leakage Current

Ω

2.3 4.6

1.2 2.4

Output PFET Resistance

0.3 0.5 0.7

0.35 0.5 0.65

µA0.1 1LX Leakage Current

Ω

0.9 2.0

LX On-Resistance

0.6 1.3

µA3 6IN Input Current

nA1 50FB Input Current

mV70FB Dual-Mode Trip Threshold

4.8 5.2

V0.9

V1.8 11.0Input Voltage

Startup Voltage

1.21 1.25 1.29

V1.21 1.25 1.29Reference Voltage

µA0.1 1Shutdown Quiescent Current

µA85 125Quiescent Current

4.75 5.00 5.25

V1.25 5.5

Output Voltage Adjustment
Range

%/mA0.003Output Load Regulation

%/V0.15Output Line Regulation

UNITSMIN TYP MAXPARAMETER

V

3.17 3.43

3.13 3.30 3.47

Output Voltage

FB = GND,
I

OUT

= 0mA to

150mA

TA= 0°C to +85°C
TA= -40°C to +85°C
TA= 0°C to +85°C
TA= -40°C to +85°C

V

1.20 1.30

FB Voltage

TA= 0°C to +85°C
TA= -40°C to +85°C

ILIM = PS

A

0.5 0.8 1.1

LX Current Limit

0.6 0.8 1.0

TA= 0°C to +85°C
TA= -40°C to +85°C
TA= 0°C to +85°C
TA= -40°C to +85°C

3/5 = PS

OUT = FB

3/5 = GND

MAX1672

Step-Up/Down DC-DC Converter

in QSOP Package

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VPS= 6V, C

REF

= 0.1µF, C

OUT

= 4.7µF, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)

Note 1: Specifications to -40°C are guaranteed by design.

ONA, ONB, 3/5; ILIM

TA= 0°C to +85°C

V

PGO

= 11V

I

PGO

= 2mA, V

PGI

= 1.2V

CONDITIONS

mV30Hysteresis

°C20

°C150Thermal Shutdown Threshold

Thermal Shutdown Hysteresis

V0.4Input Low Voltage

1.21 1.29

µA0.1 1

PGO Output Leakage

V0.1 0.4

PGO Output Low Voltage

UNITSMIN TYP MAXPARAMETER

ONA, ONB, 3/5; ILIM

V1.6Input High Voltage

__________________________________________Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

100

50

0.1 1 10 100 1000

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT

= 5V)

60

MAX1672-01

OUTPUT CURRENT (mA)

EFFICIENCY (%)

70

80

90

VIN = 5V

VIN = 3.6V

VIN = 1.8V

VIN = 0.9V

VIN = 2.7V

100

50

0.1 1 10 100 1000

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT

= 3.3V)

60

MAX1672-02

OUTPUT CURRENT (mA)

EFFICIENCY (%)

70

80

90

VIN = 3.3V

VIN = 1.8V

VIN = 0.9V

VIN = 2.7V

50

60

70

80

90

100

0 4 52 31 6 7 8 9 10

EFFICIENCY vs. INPUT VOLTAGE

(I

OUT

= 10mA)

MAX1672-03

INPUT VOLTAGE (V)

EFFICIENCY (%)

V

OUT

= 3.3V

V

OUT

= 5V

V

PGI

= 1.3V nA1 50PGI Input Bias Current

ONA, ONB, 3/5, ILIM

nA1 100Input Bias Current

TA= -40°C to +85°C

V

1.19 1.25 1.31

PGI Threshold Voltage

PGI/PGO COMPARATOR

LOGIC AND CONTROL INPUTS

MAX1672

Step-Up/Down DC-DC Converter
in QSOP Package

4 _______________________________________________________________________________________

_____________________________Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)

0

100

200

300

400

0 21 3 4

MAXIMUM OUTPUT CURRENT vs.

INPUT VOLTAGE (V

OUT

= 5V)

MAX1672-04

INPUT VOLTAGE (V)

MAXIMUM OUTPUT CURRENT (mA)

MAXIMUM RECOMMENDED
OUTPUT CURRENT

ILIM = GND (0.5A)

ILIM = PS (0.8A)

0

100

200

300

400

0 21 3 4

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE (V

OUT

= 3.3V)

MAX1672-05

INPUT VOLTAGE (V)

MAXIMUM OUTPUT CURRENT (mA)

MAXIMUM RECOMMENDED
OUTPUT CURRENT

ILIM = GND (0.5A)

ILIM = PS (0.8A)

0

100

200

300

400

4 5 7 8 9 116 10 12

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE

(POWER DISSIPATION LIMIT)

MAX1672-06

INPUT VOLTAGE (V)

MAXIMUM OUTPUT CURRENT (mA)

MAXIMUM RECOMMENDED
OUTPUT CURRENT

V

OUT

= 5V

V

OUT

= 3.3V

TA = +25°C
T

A

= +85°C

V

OUT

= 3.3V

V

OUT

= 5V

MAXIMUM RECOMMENDED INPUT VOLTAGE

1000

10

0 1 2 3 4 5 6 7 8 9 10 11

NO-LOAD BATTERY CURRENT

vs. INPUT VOLTAGE

MAX1672-07

INPUT VOLTAGE (V)

SUPPLY CURRENT (µA)

100

V

OUT

= 5V

V

OUT

= 3.3V

A

B

2ms/div

LINE-TRANSIENT RESPONSE

MAX1672-10

A: V

OUT

= 5V (100mV/div, AC COUPLED)

B: V

IN

= 2V TO 4V (I

OUT

= 100mA)

1

0.01
0 1 2 3 4 5 6 7 8 9 10 11

SHUTDOWN CURRENT

vs. INPUT VOLTAGE

MAX1672-08

INPUT VOLTAGE (V)

SUPPLY CURRENT (µA)

0.1

70

10

0.01 1 10 1000.1 1000

LINEAR REGULATOR POWER-SUPPLY

REJECTION RATIO vs. FREQUENCY

20

MAX1672-09

FREQUENCY (kHz)

PSRR (dB)

30

40

60

50

A

B

2ms/div

LOAD-TRANSIENT RESPONSE

MAX1672-11

A: V

OUT

= 5V (50mV/div, AC COUPLED)

B: I

OUT

= 10mA TO 100mA (VIN = 2V)

A

B

10µs/div

OUTPUT RIPPLE (MEDIUM LOAD)

MAX1672-12

A: V

OUT

= 5V (20mV/div, AC COUPLED)

B: I

L1

(500mA /div) (VIN = 2.7V, I

OUT

= 80mA)

MAX1672

Step-Up/Down DC-DC Converter

in QSOP Package

_______________________________________________________________________________________ 5

______________________________________________________________Pin Description

NAME FUNCTION

1 LX Inductor Connection to the Drain of the Internal N-Channel Power MOSFET

PIN

_____________________________Typical Operating Characteristics (continued)

(TA = +25°C, unless otherwise noted.)

A

B

10µs/div

OUTPUT RIPPLE (HEAVY LOAD)

MAX1672-13

A: V

OUT

= 5V (20mV/div, AC COUPLED)

B: I

L1

(500mA /div) (VIN = 2.7V, I

OUT

= 250mA)

A

B

50µs/div

START-UP DELAY

MAX1672-14

A: V

OUT

= (2V/div)

B: ONB (2V/div) (V

IN

= 2.7V, R

LOAD

= 50Ω)

A
B

200µs/div

TURN-OFF DELAY

MAX1672-15

A: V

OUT

= (2V/div)

B: ONB (2V/div) (V

IN

= 2.7V, R

LOAD

= 50Ω)

2 PGND Power Ground
3

ONB

On Control Input. When ONB = low or ONA = high, the IC is on. Connect ONB to GND for normal operation
(Table 1).

4 ONA

On Control Input. When ONA = low and ONB = high, the IC is off. Connect ONA to PS for normal operation
(Table 1).

5

3/5

Output Voltage Selection Input. Connect to PS for 3.3V output and to GND for 5V output. With VFB> 80mV,

the state of the 3/5 pin is ignored. (Table 2).
6 PGI Low-Battery Detector Input (1.25V threshold)
7

PGO Low-Battery Detector Output (open drain). PGO pulls low when V

PGI

is greater than 1.25V.
8 ILIM Inductor-Current-Limit Selection Input. Connect to PS for 0.8A current limit and to GND for 0.5A current limit.
9 OUT Regulator Output. Drain of internal PFET linear regulator. Bypass with a 4.7µF capacitor to GND.

10 FB

Feedback Input. For 3.3V or 5V output, connect to GND. For adjustable output, connect to feedback resistor­divider network. With V

FB

> 70mV, the state of the 3/5 pin is ignored.

11 PS

Bootstrapped Power Supply. Output of step-up switch-mode regulator and source of internal PFET linear
regulator. The IC is powered from this pin.

12 IN Input Voltage Sense Input. Connect to input supply.
13 REF Reference Voltage Output. Bypass with a 0.1µF capacitor to GND.
14 GND Analog Ground
15 PGND Power Ground
16 LX Inductor Connection to the Drain of the Internal N-Channel Power MOSFET

MAX1672

Step-Up/Down DC-DC Converter
in QSOP Package

6 _______________________________________________________________________________________

N

LX

ILIM

PGND

PS

OUT

100mV

MAX1672

∆T

ON

FIXED T

OFF

GENERATOR

DRV

REF

ERROR
AMP 2

ERROR
AMP 1

INPUT
MONITOR

CURRENT-LIMIT
COMPARATOR

OFF

FB

REFERENCE

GENERATOR

P

FB

FB1

FB2

REF + OFFSET

REF

PS

N

REF

PGI

PGO

3/5

FB

REF

ONB

ONA

IN

OUT

70mV

N

GND

Figure 1. Functional Diagram

MAX1672

Step-Up/Down DC-DC Converter

in QSOP Package

_______________________________________________________________________________________ 7

_______________Detailed Description

The MAX1672 integrates a step-up, switch-mode DC­DC converter with a linear regulator to provide step­up/down voltage conversion. The step-up converter
contains an N-channel power MOSFET switch, while
the linear regulator contains a P-channel MOSFET pass
element (Figure 1). The step-up converter and the lin­ear regulator share the same precision voltage refer­ence. The MAX1672’s input range is from +1.8V to
+11V, and the regulated output is internally preset to
+3.3V or +5V, or can be adjusted with two external
resistors. Boost efficiency typically exceeds 80% over a
2mA to 200mA load range. The device is bootstrapped
with chip power derived from the stepped-up voltage
output at PS. The MAX1672 typically starts up with a

0.9V input.
The MAX1672’s step-up/linear-regulator configuration

permits the use of a physically smaller inductor than
competing SEPIC and flyback configurations because
the 1/2LI2requirements of a step-up converter are half
those of SEPIC and flyback converters. Also, high-fre­quency switching and selectable peak inductor current
limit allow for low inductor value (10µH) and low current
saturation rating, respectively, further reducing the
inductor’s physical dimensions.

The MAX1672 maximizes efficiency in both step-up and
step-down operation. In step-up mode, when VIN<
V

OUT

, only the step-up regulator is active, while the lin­ear regulator behaves as a 1.2Ω (at 5V output) PFET
switch. This provides optimum efficiency (typically
85%).

In low-dropout, step-down operation, when VINis slight­ly greater than V

OUT

, both the step-up regulator and
linear regulator are active. The step-up regulator is
automatically enabled to maintain headroom across the
linear regulator (typically 1V above the 5V output). In
this case, boost ripple is rejected by the linear regula­tor, and OUT remains in regulation with no dropout.

In normal step-down operation, when VINis significantly
greater than V

OUT

, only the linear regulator is active.

The mode of operation is automatically controlled on­chip through the IN pin, which compares VINand
V

OUT

. Transitions between step-up, low-dropout step­down, and normal step-down operation are stable, but
can be seen as small variations in the output DC level
and output ripple.

Step-Up Switch-Mode Converter

A pulse-frequency-modulation (PFM) control scheme,
with a constant 1µs off-time and variable on-time, con­trols the N-channel MOSFET switch. A pulse is initiated
whenever OUT falls out of regulation. The N-channel
switch then turns off when the inductor current reaches
the peak current limit or after the 4µs maximum on-time,
whichever occurs first. This control architecture pro­vides high-efficiency, discontinuous inductor current
under light loads as well as continuous inductor current
under heavy loads. The switching frequency and output
ripple are a function of load current and input voltage.

Linear Regulator

The low-dropout linear regulator consists of a refer­ence, an error amplifier, and a P-channel MOSFET. The
reference is connected to the error amplifier input. The
error amplifier compares this reference with the select­ed feedback voltage and amplifies the difference. The
difference is conditioned and applied to the P-channel
pass transistor’s gate.

ILIM

The current-limit-select input, ILIM, selects between the
two peak inductor current limits: 0.8A (ILIM = PS) and

0.5A (ILIM = GND). If the application requires low out­put current (see

Typical Operating Characteristics

),
select 0.5A. The lower peak current limit allows for a
smaller, lower-cost inductor, and reduced output ripple.

On/Off Control

The MAX1672 is turned on or off by logic inputs ONA
and ONB (Table 1). When ONA = 1 or ONB = 0, the
device is on. When ONA = 0 and ONB = 1, the device
shuts down (see the

Applications Information

section).
For normal (on) operation, connect ONA to PS and
ONB to GND. Shutdown mode turns off the MAX1672
completely, disconnecting the input from the output
and actively pulling OUT to GND.

ONB

MAX1672

0 0 On
0 1 Off

ONA

1 0 On
1 1 On

Table 1. On/Off Logic Control

MAX1672

Step-Up/Down DC-DC Converter
in QSOP Package

8 _______________________________________________________________________________________

__________________Design Procedure

Output Voltage Selection

For fixed output voltages of 3.3V or 5V, connect 3/5 to
PS or GND and connect FB to GND (Table 2).
Alternatively, adjust the output voltage from 1.25V to

5.5V by connecting two resistors, R1 and R2 (Figure 2),
which form a voltage divider between OUT and FB.
Choose resistor values as follows:

R1 = R2[(V

OUT

/ V

REF

) -1]

where V

REF

= 1.25V. Since the input bias current at FB
has a maximum value of 50nA, R1 and R2 can be large
with no significant accuracy loss. Choose R2 in the
100kΩ to 270kΩ range and calculate R1 using the
above formula. For 1% error, the current through R1
should be at least 100 times FB’s bias current.

Whenever the voltage at FB exceeds 70mV above
GND, the state of the 3/5 pin is ignored. Connect 3/5 to
GND when adjusting V

OUT

with a resistor divider. Never

leave 3/5 unconnected.

Low-Battery Detection

The MAX1672 contains a comparator for low-battery
detection. If the voltage at PGI falls below V

REF

(typical­ly 1.25V), the open-drain comparator output (PGO)
goes high. Hysteresis is typically 30mV. Set the low­battery detector’s threshold with resistors R3 and R4
(Figure 2) using the following equation:

R3 = R4[(V

PGT

/ V

REF

) -1]

where V

PGT

is the desired threshold of the low-battery

detector and V

REF

= 1.25V. Since the input bias current
at PGI has a maximum value of 50nA, R3 and R4 can
be large to minimize input loading with no significant
accuracy loss. Choose R4 in the 100kΩ to 270kΩ range
and calculate R3 using the above formula. For 1%
error, the current through R3 should be at least 100
times PGI’s bias current.

The PGO output is open-drain and should be pulled
high with external resistor R5 for normal operation. If the
low-battery comparator is not used, connect PGI and
PGO to GND.

Inductor Selection

A 10µH inductor performs well in most MAX1672 appli­cations. Smaller inductor values typically offer a smaller
physical size for a given series resistance, but may
increase switching losses. Larger inductor values
exhibit higher output current capability and larger phys­ical dimensions for a given series resistance. For opti­mum performance, choose an inductor value from
Table 3 or by using the following equation:

where I

LIM

is the peak switch-current limit, which is

0.8A for I

LIM

= PS and 0.5A for I

LIM

= GND.

The inductor’s incremental saturation current rating
should also be greater than the peak switch-current
limit. However, it is generally acceptable to bias most
inductors into saturation by as much as 20% with slight­ly reduced efficiency. The inductor’s DC resistance sig­nificantly affects efficiency. See Tables 4 and 5 for a list
of suggested inductors and suppliers.

V + V

I

V + V

I

OUT DIODE

LIM

IN(min) SWITCH

LIM

( )

<

<

( )

t L

t

OFF

ON

2

(max)

MAX1672

IN

ONA

PGI

ONB

OFF

ON

C3

0.1µF

C1

100µF

C2
100µF

R2

R1

R5
1M

C4

4.7µF

R3

R4

L1

10µH

PGND GND

PS

1.25V TO

5.5V OUTPUT

INPUT

1.8V TO 11V

LOW-BATTERY­DETECTOR
OUTPUT

OUT

PG0

FB

REF

LX

OFF

3/5

ILIM

0.8A

ON

0.5A

Figure 2. Adjustable Output Voltage Configuration

Table 2. Output Voltage Control

FB V

OUT

(V)

0 GND +5
1 GND +3.3

3/

55

X >70mV +1.25 to +5.5

MAX1672

Step-Up/Down DC-DC Converter

in QSOP Package

_______________________________________________________________________________________ 9

Capacitor Selection

The equivalent series resistance (ESR) of both bypass
and filter capacitors affects efficiency and output rip­ple. Output voltage ripple is the product of peak induc­tor current and filter capacitor ESR. Use low-ESR
capacitors for best performance, or connect two or
more filter capacitors in parallel.

A 100µF, 16V, input bypass capacitor (C1) with low
ESR reduces peak battery currents and reflected noise
due to inductor current ripple. Smaller ceramic capaci­tors may also be used for light loads or in applications
that can tolerate higher input ripple.

A 100µF, 16V, surface-mount (SMT) tantalum PS filter
capacitor (C2) with 0.1Ω ESR typically exhibits 20mV
output ripple (at OUT) when stepping up from 2V to 5V
at 100mA load. Smaller capacitors (down to 10µF with
higher ESR) are acceptable for light loads or in applica­tions that can tolerate higher output ripple.

Only 4.7µF is needed at OUT (C4) to maintain linear
regulator stability. During boost operation, this capaci­tor reduces output voltage spikes from the step-up con­verter by forming an R-C lowpass filter along with the
P-channel MOSFET on-resistance. Output ripple can be
further reduced by increasing C4.

See Tables 4 and 5 for a list of suggested capacitors
and suppliers.

Diode Selection

The MAX1672’s high switching frequency demands a
high-speed rectifier. Schottky diodes, such as the
1N5817 or MBRS130T3, are recommended. Make sure
the diode’s current rating exceeds the maximum load
current. See Tables 4 and 5 for a list of suggested
diodes and suppliers.

Table 3. Suggested Inductor Values Table 4. Suggested Components

ILIM

INDUCTOR VALUE

(µH)

0 (5V) 0 (0.5A) 10 to 22
0 (5V) 1 (0.8A) 10

3/

55

1 (3.3V) 0 (0.5A) 10
1 (3.3V) 1 (0.8A) 4.7 to 10

INDUCTORS

Sumida

CD43-100 (1.04A, 0.182Ω)
CD54-100 (1.44A, 0.100Ω)
CDRH73-100 (1.68A, 0.072Ω)

L1

10µH

Coilcraft

DT1608C-103 (0.7A, 0.095Ω)

CAPACITORS

AVX

TPSE Series

Sprague

593D or 595D Series

Tantalum

DIODES

Motorola

MBRS130LT3 (1.0A, 30V)
MBR0520LT3 (0.5A, 20V)

Schottky

1N5817 Equivalent

International Rectifier

10BQ40 (1.0A, 40V)

Table 5. Component Suppliers

PHONE

AVX [phone]
Coilcraft [phone]

SUPPLIER

International
Rectifier

[phone]

Motorola [phone]

FAX

[phone]
[phone]

[phone]

[phone]
Sanyo [phone] [phone]
Sprague [phone] [phone]
Sumida [phone] [phone]

MAX1672

Step-Up/Down DC-DC Converter
in QSOP Package

10 ______________________________________________________________________________________

__________Applications Information

Using a Single, Pushbutton On/Off Switch

A single pushbutton switch can be used to turn the
MAX1672 on and off. As shown in Figure 3, ONA is
pulled low and ONB is pulled high when the part is off.
When the momentary switch is pressed, ONB is pulled
low and the regulator turns on. The switch should be on
long enough for the µC to exit reset. The controller
issues a logic high to ONA, which guarantees the part
will stay on regardless of the switch state.

To turn off the regulator, press the switch again. The
controller reads the switch status and pulls ONA low.
When the switch is released, ONB goes high, turning
off the MAX1672.

Thermal Overload Protection

Thermal overload protection limits total power dissipa­tion in the MAX1672. When the junction temperature
exceeds TJ= +150°C, the pass transistor turns off,
allowing the MAX1672 to cool. The pass transistor turns
on again after the IC’s junction temperature cools by
20°C, resulting in a pulsed output during thermal over­load conditions.

Thermal overload protection is designed to protect the
MAX1672 if fault conditions occur. It is not intended to
be used as an operating mode. Prolonged operation in
thermal shutdown mode may reduce the IC’s reliability.
For continual operation, do not exceed the absolute
maximum junction temperature rating TJ= +150°C.

Power Dissipation and Operating Region

The MAX1672’s maximum power dissipation in step­down mode depends on the thermal resistance of the
case and circuit board, the temperature difference
between the die junction and ambient air, and the air
flow rate. The power dissipated in the device is
P = I

OUT(VIN

- V

OUT

) during step-down operation. The

maximum power dissipation is as follows:

P

MAX

= (TJ- TA)/(θ

JB

+ θBA)

where (TJ- TA) is the temperature difference between
the MAX1672 die junction and the surrounding air, θ

JB

(or θJC) is the thermal resistance of the package, and

θBAis the thermal resistance throughout the printed cir-

cuit board, copper traces, and other materials to the
surrounding air. The MAX1672’s thermal resistance is
120°C/W. See the

Typical Operating Characteristics

for

Maximum Output Current vs. Input Voltage.

Layout Considerations

Proper PC board layout is essential to minimize noise
due to high inductor current levels and fast switching
waveforms. To maximize output power and efficiency
and minimize output ripple voltage and ground noise,
use the following guidelines when designing your
board:

• Use a ground plane.

• Keep the IC’s GND pin and the ground leads of C1

and C2 (Figure 2) less than 0.2in. (5mm) apart.

• Make all connections to the FB and LX pins as short
as possible.

• Solder the IC’s GND pin directly to the ground
plane.

Refer to the MAX1672 EV kit for a suggested PC board
layout.

MAX1672

ONA

ONB

1M

1M

I/O

I/O

OUT

V

DD

µ

C

Figure 3. Momentary Pushbutton On/Off Control

MAX1672

Step-Up/Down DC-DC Converter

in QSOP Package

______________________________________________________________________________________ 11

________________________________________________________Package Information

QSOP.EPS

MAX1672

Step-Up/Down DC-DC Converter
in QSOP Package

12 ______________________________________________________________________________________

NOTES