Rainbow Electronics MAX1643 User Manual

_______________General Description

The MAX1642/MAX1643 are high-efficiency, low-voltage,
step-up DC-DC converters intended for devices pow­ered by a single alkaline cell. They feature low quies­cent supply currents and are supplied in the ultra-small
µMAX package, which is only 1.1mm high. The guaran­teed start-up voltage is 0.88V.

Each device consists of an internal 1Ω, N-channel
MOSFET power switch; a built-in synchronous rectifier
that acts as the catch diode; an oscillator; a reference;
and pulse-frequency-modulation (PFM) control circuitry.
Both devices feature an independent undervoltage
comparator (PFI/PFO). The MAX1642 also includes a
2µA logic-controlled shutdown mode. The MAX1643
offers a dedicated low-battery detector (BATTLO) in
lieu of shutdown.

The output voltage for each device is preset to 3.3V
±4%, or can be adjusted from +2V to +5.2V using only
two resistors.

________________________Applications

Pagers
Remote Controls
Pointing Devices
Personal Medical Monitors
Single-Cell Battery-Powered Devices

____________________________Features

♦ Built-In Synchronous Rectifier
♦ 0.88V Guaranteed Start-Up
♦ Ultra-Small µMAX Package: 1.1mm High
♦ 83% Efficiency
♦ 4µA Quiescent Supply Current into BATT Pin
♦ 2µA Logic-Controlled Shutdown (MAX1642)
♦ Two Undervoltage Detectors (MAX1643)
♦ 2V to 5.2V Output Range
♦ 20mA Output Current at 1.2V Input
♦ Reverse Battery Protection

MAX1642/MAX1643

High-Efficiency, Step-Up

DC-DC Converters for 1V Inputs

________________________________________________________________

Maxim Integrated Products

1

GND

PFO

FB

SHDN

1

2

8

7

OUT
LX

PFI

BATT

MAX1642

µMAX

TOP VIEW

3

4

6

5

GND

BATTLO

FB

PFO

1

2

8

7

OUT
LX

PFI

BATT

MAX1643

µMAX

3

4

6

5

_________________Pin Configurations

OUT

OUTPUT

3.3V

INPUT

0.88V TO 1.65V

100µH

22µF

22µF

ON

LOW-BATTERY

DETECTOR INPUT

LOW-BATTERY
DETECTOR OUTPUT

OFF

PFO

BATT

LX

MAX1642

SHDN
PFI

GND FB

__________Typical Operating Circuit

______________Ordering Information

PART

MAX1642C/D

MAX1642EUA
MAX1643C/D

0°C to +70°C

-40°C to +85°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

Dice*
8 µMAX
Dice*

MAX1643EUA -40°C to +85°C 8 µMAX

EVALUATION KIT MANUAL

FOLLOWS DATA SHEET

19-1183; Rev 0; 6/97

*

Dice are tested at TA= +25°C.
Note: To order these devices shipped in tape and reel, add a -T

to the part number.

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

MAX1642/MAX1643

High-Efficiency, Step-Up
DC-DC Converters for 1V Inputs

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

BATT to GND...........................................................-0.3V to 6.0V

BATT Forward Current..........................................................0.5A

OUT to GND.............................................................-0.3V to 6.0V

OUT, LX Current.......................................................................1A

LX to GND................................................................-0.3V to 6.0V

SHDN, FB, BATTLO, PFO to GND...........................-0.3V to 6.0V

PFI to GND............................................................-0.3V to V

BATT

Reverse Battery Current (TA= +25°C) (Note 1) ...............220mA

Continuous Power Dissipation

µMAX (derate 4.1mW/°C above 70°C)..........................330mW

Operating Temperature Range

MAX1642EUA/MAX1643EUA ............................-40°C to +85°C

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

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

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

RL= 3kΩ, TA= +25°C

VFB= 1.3V

I

LOAD

= 20mA

V

BATT

= 1.0V (MAX1642)

0.9V < V

BATT

< 1.5V (tON= K / V

BATT

)

V

OUT

= 3.5V (MAX1642)

I

DIODE

= 100mA, P-channel switch off

V

OUT

= 3.3V

VFB< 0.1V
External feedback
External feedback

V

OUT

= 3.5V

V

OUT

= 3.3V

0.9V < V

BATT

< 1.5V, V

OUT

= 3.3V

CONDITIONS

nA10FB Input Current

%80

η

Efficiency

µA2 3.5I

SHDN,BATT

Shutdown Current into BATT

µA0.1 1I

SHDN,OUT

Shutdown Current into OUT

µA4 6.5I

QBATT

Quiescent Current into BATT

µA11 18I

QOUT

Quiescent Current into OUT

1 1.5RATIOOff-Time Tracking Ratio (Note 3)

mV/°C-2Start-Up Voltage Tempco

V0.88

V0.7V

BATT(MIN)

Minimum Operating Input Voltage

Start-Up Voltage (Note 2)

V-µs17 25 35KOn-Time Constant

V0.8P-Channel Catch-Diode Voltage

Ω1.5 2.2P-Channel On-Resistance

V3.16 3.30 3.44V

OUT

Output Voltage

V2.0 5.2Output Voltage Range
V1.18 1.225 1.27V

FB

FB Set Voltage

Ω1 1.5N-Channel On-Resistance

UNITSMIN TYP MAXSYMBOLPARAMETER

ELECTRICAL CHARACTERISTICS

(V

BATT

= V

SHDN

= 1.3V, I

LOAD

= 0mA, FB = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

Note 1: The reverse battery current is measured from the

Typical Operating Circuit’s

input terminal to GND when the battery is con­nected backward. A reverse current of 220mA will not exceed package dissipation limits but, if left for an extended time
(more than 10 minutes), may degrade performance.

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.

V1.65Maximum Operating Input Voltage

Falling PFI, hysteresis = 1% mV590 614 632PFI Trip Voltage

V

PFI

= 0V, V

OUT

= 3.3V, I

SINK

= 1mA

V

PFI

= 650mV

V0.4V

OL

PFO, BATTLO Low Output Voltage

nA10PFI Input Current

V

OUT

= 3.3V, hysteresis = 2% (MAX1643)

V

PFI

= 650mV, V

PFO

= 6V

V0.96 1.0 1.04

BATTLO Trip Voltage

µA1

PFO, BATTLO Leakage Current

% of V

BATT

(MAX1642)

% of V

BATT

(MAX1642)

%80V

IH

SHDN Input High Voltage

%20V

IL

SHDN Input Low Voltage

(MAX1642) nA10

SHDN Input Current

MAX1642/MAX1643

High-Efficiency, Step-Up

DC-DC Converters for 1V Inputs

_______________________________________________________________________________________ 3

Note 2: Start-up guaranteed by correlation to measurements of device parameters (i.e., switch on-resistance, on-times, off-times, and

output voltage trip points).

Note 3: . This guarantees discontinuous conduction.

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

t =

t x V

V - V

x RATIO

OFF

ON BATT

OUT BATT











Falling PFI, hysteresis = 1%

V

BATT

= 1.0V (MAX1642)

0.9V < V

BATT

< 1.5V (tON= K / V

BATT

)

V

OUT

= 3.5V (MAX1642)

V

OUT

= 3.3V

VFB< 0.1V
External feedback

V

OUT

= 3.5V

V

OUT

= 3.3V

CONDITIONS

mV 550 662PFI Trip Voltage

µA3.5I

SHDN,BATT

Shutdown Current into BATT

µA1I

SHDN,OUT

Shutdown Current into OUT

µA6.5I

QBATT

Quiescent Current into BATT

µA18I

QOUT

Quiescent Current into OUT

V-µs12.4 38.2KOn-Time Constant

Ω2.2P-Channel On-Resistance

V2.99 3.56V

OUT

Output Voltage

V1.11 1.32V

FB

FB Set Voltage

Ω1.5N-Channel On-Resistance

UNITSMIN MAXSYMBOLPARAMETER

ELECTRICAL CHARACTERISTICS

(V

BATT

= V

SHDN

= 1.3V, I

LOAD

= 0mA, FB = GND, TA= -40°C to +85°C, unless otherwise noted.) (Note 4)

Falling V

BATT

, V

OUT

= 3.3V, hysteresis = 2%

(MAX1643)

V0.93 1.06

BATTLO Trip Voltage

__________________________________________Typical Operating Characteristics

(Circuit of Figure 4, V

BATT

= 1.2V, R1 + R2 = 1MΩ, TA = +25°C, unless otherwise noted.)

0

0.01 1 100.1 100

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT

= 2.4V)

10

MAX1642/43 TOC01A

OUTPUT CURRENT (mA)

EFFICIENCY (%)

VIN = 1.6V

L1 = 100µH
SUMIDA CD54-101

VIN = 1.2V

VIN = 0.85V

VIN = 1.0V

20

30

40

50

60

70

80

90

100

0

0.01 1 100.1 100

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT

= 2.4V)

10

MAX1642/43 TOC01B

OUTPUT CURRENT (mA)

EFFICIENCY (%)

VIN = 1.6V

L1 = 150µH
TDK NLC565050T-151K

VIN = 1.2V

VIN = 0.85V

VIN = 1.0V

20

30

40

50

60

70

80

90

100

0

0.01 1 100.1 100

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT

= 3.3V)

10

MAX1642/43 TOC02A

OUTPUT CURRENT (mA)

EFFICIENCY (%)

VIN = 1.6V

L1 = 100µH
SUMIDA CD54-101

VIN = 1.2V

VIN = 0.85V

VIN = 1.0V

20

30

40

50

60

70

80

90

100

MAX1642/MAX1643

High-Efficiency, Step-Up
DC-DC Converters for 1V Inputs

4 _______________________________________________________________________________________

0.6
0

MINIMUM START-UP INPUT VOLTAGE

vs. OUTPUT CURRENT

0.7

0.8

MAX1642/43 TOC07b

OUTPUT CURRENT (mA)

START-UP INPUT VOLTAGE (V)

12 14

1.2

1.1

1.5

1.4

1.3

0.9

1.0

2 4 6 10

16

1.6

8

L1 = 150µH
TDK NLC565050T-151K

V

OUT

= 5V

V

OUT

= 2.4V, 3.3V

0.6
0

MINIMUM START-UP INPUT VOLTAGE

vs. OUTPUT CURRENT

0.7

0.8

MAX1642/43 TOC07a

OUTPUT CURRENT (mA)

START-UP INPUT VOLTAGE (V)

20

1.2

1.1

1.5

1.4

1.3

0.9

1.0

5 15 25

1.6

10

L1 = 100µH
SUMIDA CD54-101

V

OUT

= 5V

V

OUT

= 2.4V, 3.3V

____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 4, V

BATT

= 1.2V, R1 + R2 = 1MΩ, TA = +25°C, unless otherwise noted.)

0

0.01 1 100.1 100

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT

= 3.3V)

10

MAX1642/43 TOC02B

OUTPUT CURRENT (mA)

EFFICIENCY (%)

VIN = 1.6V

L1 = 150µH
TDK NLC565050T-151K

VIN = 1.2V

VIN = 0.85V

VIN = 1.0V

20

30

40

50

60

70

80

90

100

100

90
80

0

0.01 1 100.1 100

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT

= 5.0V)

20
10

MAX1642/43 TOC03a

OUTPUT CURRENT (mA)

EFFICIENCY (%)

30

40

50

60

70

VIN = 1.6V

VIN = 0.85V

VIN = 1.0V

L1 = 100µH
SUMIDA CD54-101

VIN = 1.2V

100

90
80

0

0.01 1 100.1 100

EFFICIENCY vs. OUTPUT CURRENT

(V

OUT

= 5.0V)

20
10

MAX1642/43 TOC03b

OUTPUT CURRENT (mA)

EFFICIENCY (%)

30

40

50

60

70

VIN = 1.6V

VIN = 0.85V

VIN = 1.0V

L1 = 150µH
TDK NLC565050T-151K

VIN = 1.2V

10,000

10

0.8 1.0 1.4 1.8

NO-LOAD BATTERY CURRENT

vs. INPUT VOLTAGE

100

1000

MAX1642/43 TOC04

INPUT VOLTAGE (V)

QUIESCENT CURRENT (mA)

1.2 1.6

V

OUT

= 5.0V

V

OUT

= 2.5V OR 3.3V

0

-40

NO-LOAD BATTERY CURRENT

vs. TEMPERATURE

20

MAX1642/43 TOC05

TEMPERATURE (°C)

QUIESCENT CURRENT (µA)

60

100

120

80

40

60

-20 4020 80 100

140

0

V

BATT

= 1.2V

V

OUT

= 3.3V

0

-40

BATT AND OUT PIN QUIESCENT CURRENTS

vs. TEMPERATURE

5

MAX1642/43 TOC06

TEMPERATURE (°C)

QUIESCENT CURRENT (µA)

60

20

25

10

15

-20 4020 80 100

30

0

V

BATT

= 1.2V

V

OUT

= 3.6V

I

BATT

I

OUT

MAX1642/MAX1643

High-Efficiency, Step-Up

DC-DC Converters for 1V Inputs

_______________________________________________________________________________________

5

____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 4, V

BATT

= 1.2V, R1 + R2 = 1MΩ, TA = +25°C, unless otherwise noted.)

B

LOAD-TRANSIENT RESPONSE

MAX1642/43 TOC10

A

400µs/div

V

OUT

= 3.3V, V

BATT

= 1.2V

A: OUT, 20mV/div, 3.3V DC OFFSET
B: LOAD, 2mA to 20mA, 10mA/div

0

0.8

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE

MAX1642/43 TOC08b

INPUT VOLTAGE (V)

MAXIMUM OUTPUT CURRENT (mA)

1.4

25

30

5

15

10

20

0.9 1.31.2

1.5 1.6

35

1.0 1.1

L1 = 100µH
SUMIDA CD54-101

V

OUT

= 5V

V

OUT

= 3.3V

V

OUT

= 2.4V

0

0.8

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE

MAX1642/43 TOC08c

INPUT VOLTAGE (V)

MAXIMUM OUTPUT CURRENT (mA)

1.4

14
12

18
16

4
2

6

10

8

0.9 1.31.2

1.5 1.6

20

1.0 1.1

L1 = 150µH
TDK NLC565050T-151K

V

OUT

= 5V

V

OUT

= 3.3V

V

OUT

= 2.4V

C

SWITCHING WAVEFORMS

MAX1642/43 TOC09

B

A

10ms/div

V

OUT

= 3.3V, VIN = 1.2V, I

OUT

= 12mA

A: LX, 2V/div, L1 = TDK NLC565050T-151K
B: OUT, 20mV/div, 3.3V DC OFFSET
C: INDUCTOR CURRENT, 100mA/div

B

LINE-TRANSIENT RESPONSE

MAX1642/43 TOC11

A

400µs/div

V

OUT

= 3.3V, LOAD = 15mA

A: OUT, 50mV/div, 3.3V DC OFFSET
B: V

BATT

, 1V to 1.5V, 500mV/div

B

C

SHUTDOWN RESPONSE AND

INDUCTOR CURRENT

MAX1642/43 TOC12

A

10ms/div

V

OUT

= 3.3V, V

BATT

= 1.2V, I

OUT

= 5mA

A: OUT, 1V/div
B: INDUCTOR CURRENT, 200mA/div
C: SHDN, 2V/div

MAX1642/MAX1643

High-Efficiency, Step-Up
DC-DC Converters for 1V Inputs

6 _______________________________________________________________________________________

______________________________________________________________Pin Description

_______________Detailed Description

The MAX1642/MAX1643 each consist of an internal 1Ω,
N-channel MOSFET power switch, a built-in synchro­nous rectifier that acts as the catch diode, an oscillator,
a reference, and PFM control circuitry (Figure 1).

These devices are optimized for applications with
power-management features that operate from one
alkaline cell, such as pagers, remote controls, and bat­tery-powered instruments. They are designed to meet
the specific demands of the operating states character­istic of such systems:

1)

Primary battery is good and the load is active:

In
this state, the system draws tens of milliamperes,
and the MAX1642/MAX1643 typically offer 80% effi­ciency.

2)

Primary battery is good and the load is sleeping:

In
this state, the load is drawing hundreds of microam­peres, and the DC-DC converter IC draws very low
quiescent current. In many applications, the load is
expected to be in this state most of the time.

Operating Principle

The MAX1642/MAX1643 employ a proprietary pulse­frequency-modulation (PFM) control scheme that com­bines the ultra-low quiescent current traditional of
pulse-skipping PFM converters with the high-load effi­ciency of pulse-width-modulation (PWM) converters.
The on-time and minimum off-times are varied as a
function of the input and output voltages:

where K is typically 25V-µs. This enables the
MAX1642/MAX1643 to maintain high efficiency over a
wide range of loads and input/output voltages. The DC­DC converter is powered from the OUT pin.

t =

K

V

t =

1.2 x K

V - V

ON

BATT

OFF(MIN)

OUT BATT

6
7

8

4

—

5

2

1

MAX1643

GroundGND6
N-Channel MOSFET Switch Drain and P-Channel Synchronous-Rectifier DrainLX7
Power Output. Feedback input for fixed 3.3V operation and IC power input. Connect filter

capacitor close to OUT.

OUT8

Open-Drain Power-Fail Output. Sinks current when PFI drops below 614mV.

PFO

3

Active-Low Shutdown Input. Connect to BATT for normal operation.

SHDN

4

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

FB5

Power-Fail Input. When the voltage on PFI drops below 614mV, PFO sinks current.

PFI2

IC Battery-Power Input. Sense input for BATTLO comparator (MAX1643 only).

BATT1

PIN

3

Open-Drain Battery-Low Output. When the voltage at BATT drops below 1V, BATTLO
sinks current.

BATTLO

—

MAX1642

FUNCTIONNAME

MAX1642/MAX1643

High-Efficiency, Step-Up

DC-DC Converters for 1V Inputs

_______________________________________________________________________________________ 7

BATT

PFI

0.5REF

PFO

GND

OUT

REF

N

P

OUT 1.7V

FB

SHDN

LX

RFRDY

REF

REF

0.5REF

START-UP

OSCILLATOR

TIMING

TON

EN

PDRV

NDRV

TOFF

LOGIC

MAX1642

Figure 1. MAX1642 Functional Diagram

When the error comparator detects that the output
voltage is too low, it turns on the internal N-channel
MOSFET switch until the on-time is satisfied (see Figure
1 and the Standard Application Circuits, Figures 2 and

3). During the on-time, current ramps up in the induc­tor, storing energy in a magnetic field. When the MOS­FET turns off, during the second half of each cycle, the
magnetic field collapses, causing the inductor voltage
to force current through the synchronous rectifier,
transferring the stored energy to the output filter capac­itor and load. The output filter capacitor stores charge
while current from the inductor is high, then holds up
the output voltage until the second half of the next
switching cycle, smoothing power flow to the load.

Bootstrap DC-DC Block

The bootstrap block contains a low-voltage start-up
oscillator. This oscillator pumps up the output voltage
to approximately 1.7V, where the main DC-DC con­verter can operate. The oscillator is powered from the
BATT input and drives an NPN switch. During start-up,

the P-channel synchronous rectifier remains off and
either its body diode or an external diode is used as an
output rectifier. Reduce the load as needed to allow
start-up with input voltages below 2V (see

Typical

Operating Characteristics

).

Shutdown (MAX1642)

Pulling SHDN low places the MAX1642 in shutdown
mode (I

SHDN

= 2µA typical). In shutdown, the internal
switching MOSFET turns off, PFO goes high­impedance, and the synchronous rectifier turns off to
prevent reverse current from flowing from the output
back to the input. However, there is still a forward cur­rent path through the synchronous-rectifier body diode
from the input to the output. Thus, in shutdown, the out­put remains one diode drop below the battery voltage
(V

BATT

). To disable the shutdown feature, connect

SHDN (a logic input) to BATT.

MAX1642/MAX1643

High-Efficiency, Step-Up
DC-DC Converters for 1V Inputs

8 _______________________________________________________________________________________

BATTLO

(MAX1643)

The MAX1643 contains an on-chip comparator for low­battery detection. If the voltage at BATT drops below
1V, BATTLO sinks current. BATTLO is an open-drain
output. In combination with PFI/PFO, this allows moni­toring of both the input and output voltages.

Reverse-Battery Protection

The MAX1642/MAX1643 can sustain/survive single-cell
battery reversal up to the package power-dissipation
limit. An internal 5Ω resistor in series with a diode limits
reverse current to less than 220mA, which prevents dam­age to the MAX1642/MAX1643. Prolonged operation
above 220mA reverse-battery current can degrade the
devices’ performance.

________________Design Information

Output Voltage Selection

The MAX1642/MAX1643 operate with a 3.3V ±4% or
adjustable output. To select fixed-voltage operation, con­nect FB to GND. For an adjustable output between 2V
and 5.2V, connect FB to a resistor voltage divider
between OUT and GND (Figure 4). FB regulates to 1.23V.

Since FB leakage is 10nA max, select feedback resistor
R2 in the 100kΩ to 1MΩ range. R1 is given by:

where V

REF

= 1.23V.

Power-Fail Detection

The MAX1642/MAX1643 have an on-chip comparator for
power-fail detection. This comparator can detect loss of
power at the input or output. If the voltage at PFI falls
below 614mV, the PFO output sinks current to GND.
Hysteresis at the power-fail input is 1%. The power-fail
monitor’s threshold is set by two resistors: R3 and R4
(Figure 5). Set the threshold using the following equation:

where V

TH

is the desired threshold of the power-fail

detector, and V

PFI

is the 614mV reference of the power­fail comparator. Since PFI leakage is 10nA max, select
feedback resistor R4 in the 100kΩ to 1MΩ range.

Low-Battery Start-Up

The MAX1642/MAX1643 are bootstrapped circuits with
a low-voltage start-up oscillator. They can start under
low-load conditions at lower battery voltages than at full
load. Once started, the output can maintain the load as

the battery voltage decreases below the start-up volt­age (see

Typical Operating Characteristics

).

Inductor Selection

A 100µH inductor is recommended for most appli­cations. The use of lower inductor values (down to
68µH) increases maximum output current. Higher val­ues (up to 220µH) reduce peak inductor current and
consequent ripple and noise. The inductor’s saturation­current rating must exceed the peak current limit syn­thesized by the MAX1642/MAX1643’s timing
algorithms:

where K

MAX

= 35V-µs. The maximum recommended

I

PEAK

is 350mA. For best efficiency, inductor series

resistance should be less than 1Ω.

I =

K

L

PEAK

MAX

MIN

R3 = R4

V
V

- 1

TH
PFI











R1 = R2

V

V

- 1

OUT

REF











MAX1642

GND FB

BATT
PFI

3.3V

OUT

0.88V to 1.65V INPUT

100µH, 350mA

PF0

22µF0.1µF

SHDN

LX

OUT

OUT

22µF 0.1µF

Figure 2. MAX1642 3.3V Standard Application Circuit

Figure 3. MAX1643 3.3V Standard Application Circuit

0.88V to 1.65V INPUT

22µF

100µH, 350mA

0.1µF
BATT

OUT

MAX1643

BATTLO

GND FB

LX

OUT

PFI

PFO

3.3V

OUT

22µF0.1µF

MAX1642/MAX1643

High-Efficiency, Step-Up

DC-DC Converters for 1V Inputs

_______________________________________________________________________________________ 9

Capacitor Selection

Choose input and output capacitors to service input
and output peak currents with acceptable voltage rip­ple. A 22µF, 6V, low-ESR, surface-mount tantalum out­put filter capacitor typically provides 60mV output
ripple when stepping up from 1.3V to 3.3V at 20mA.
The input filter capacitor (CIN) also reduces peak cur­rents drawn from the battery and improves efficiency.

Low equivalent series resistance (ESR) capacitors are
recommended. Capacitor ESR is a major contributor to
output ripple (usually more than 60%). Ceramic capaci­tors have the lowest ESR, but low-ESR tantalums repre­sent a good balance between cost and performance.
Low-ESR aluminum electrolytic capacitors are tolerable,
and standard aluminum electrolytic capacitors should
be avoided. Do not exceed tantalum capacitors’ ripple­current ratings; select capacitors with a rating exceed­ing the peak inductor current (I

PEAK

).

PC Board Layout and Grounding

High switching frequencies and large peak currents
make PC board layout an important part of design. Poor
design can result in excessive EMI on the feedback paths
and voltage gradients in the ground plane. Both of these
factors can result in instability or regulation errors. The
OUT pin must be bypassed directly to GND as close to
the IC as possible (within 0.2 in. or 5mm).

Place power components—such as the MAX1642/
MAX1643, inductor, input filter capacitor, and output filter
capacitor—as close together as possible. Keep their
traces short, direct, and wide (≥50 mil or 1.25mm), and
place their ground pins close together in a star-ground
configuration. Keep the extra copper on the board and
integrate it into ground as a pseudo-ground plane. On
multilayer boards, route the star ground using compo­nent-side copper fill, then connect it to the internal ground
plane using vias.

Place the external voltage-feedback network very close to
the FB pin (within 0.2 in. or 5mm). Noisy traces, such as
from the LX pin, should be kept away from the voltage­feedback network and separated from it using grounded
copper. The evaluation kit manual shows an example PC
board layout, routing, and pseudo-ground plane.

Noise and Voltage Ripple

EMI and output voltage ripple can be minimized by fol­lowing a few simple design rules.

1) Place the DC-DC converter and digital circuitry on
an opposite corner of the PC board, away from sen­sitive RF and analog input stages.

2) Use a closed-core inductor, such as toroid or
shielded bobbin, to minimize fringe magnetic fields.

3) Choose the largest inductor value that satisfies the
load requirement to minimize peak switching cur­rent and resulting ripple and noise.

4) Use low-ESR input and output filter capacitors.

5) Follow sound circuit-board layout and grounding
rules (see the

PC Board Layout and Grounding

section).

6) Where necessary, add LC pi filters, linear post-reg­ulators such as the MAX8863 and MAX8864
(SOT23 package), or shielding. The LC pi filter’s
cutoff frequency should be at least a decade or two
below the DC-DC converter’s switching frequency
for the specified load and input voltage.

MAX1642

GND

BATT
PFI

V

OUT

= 2V

TO 5.2V

0.88V to 1.65V INPUT

*OPTIONAL COMPENSATION

100µH

PF0

100pF*

SHDN

LX

OUT

FB

R1

R2

OUT

22µF 0.1µF

Figure 4. Adjustable-Output Circuit

Figure 5. Power-Fail Detection Circuit

V

TH

MAX1642
MAX1643

PFI

R3

R4

MAX1642/MAX1643

High-Efficiency, Step-Up
DC-DC Converters for 1V Inputs

10 ______________________________________________________________________________________

Table 2. Surface-Mount Inductor Information

Table 1. Component Suppliers

SUPPLIER PHONE FAX

AVX USA

[phone] [phone]

[phone]
Coilcraft USA [phone] [phone]
Coiltronics USA [phone] [phone]
Dale USA [phone] [phone]

Nichicon

USA [phone] [phone]
Japan 81-7-5231-8461 81-7-5256-4158

Sanyo

USA [phone] [phone]
Japan 81-7-2070-6306 81-7-2070-1174

Sprague USA [phone] [phone]
Sumida

USA [phone] [phone]
Japan 81-3-3607-5111 81-3-3607-5144

TDK USA [phone] [phone]

TRANSISTOR COUNT: 594
SUBSTRATE CONNECTED TO GND

__________________ Chip Information

Sumida CD54-221 1.57 350

220

I

SAT

(mA)

RESISTANCE

(Ω)

Coilcraft DO1608-154

Coilcraft DO1608-224 2.3 220

Sumida CD54-151 1.1

1.7
400

270

Coilcraft DO1608-104
Sumida CD54-101 0.7100

1.1
520

310

Sumida CD54-680 0.46

68

610

400

INDUCTOR SPECIFICATION

VENDOR/PART

Coilcraft DO1608-683

INDUCTANCE

(µH)

TDK NLC565050T-101K 1.6 250

0.75

150

TDK NLC565050T-151K 2.2 210

MAX1642/MAX1643

High-Efficiency, Step-Up

DC-DC Converters for 1V Inputs

______________________________________________________________________________________ 11

________________________________________________________Package Information

8LUMAXD.EPS

MAX1642/MAX1643

High-Efficiency, Step-Up
DC-DC Converters for 1V Inputs

12 ______________________________________________________________________________________

NOTES