Rainbow Electronics MAX1685 User Manual

General Description

The MAX1684/MAX1685 are high-efficiency, internal­switch, pulse-width modulation (PWM) step-down switch­ing regulators intended to power cellular phones,
communicating PDAs, and handy-terminals. These
devices deliver a guaranteed 1A output current from two
lithium-ion (Li+) batteries. Their wide-input voltage range
of 2.7V to 14V gives design flexibility and allows batteries
to charge from a wall cube, since the ICs operate at the
higher voltages that occur when the battery is removed.
The output voltage is preset to 3.3V or can be externally
adjusted from 1.25V to VIN.

The low on-resistance power switch and built-in synchro­nous rectifier provide high efficiencies of up to 96%.
There are four modes of operation: fixed-frequency, nor­mal, low-power, and shutdown. The fixed-frequency
PWM mode of operation offers excellent noise character­istics. The normal mode maintains high efficiency at all
loads. The low-power mode is used to conserve power in
standby or when full load is not required. The shutdown
mode is used to power down the device for minimal cur­rent draw.

The MAX1684 runs at 300kHz for applications that
require highest efficiency. The MAX1685 runs at
600kHz to allow the use of smaller external compo­nents. These devices can also be synchronized to an
external clock. Other features include a 100% duty
cycle for low-dropout applications, an auxiliary 3V/5mA
output, and a 1% accurate reference.

Both devices are available in a space-saving 16-QSOP
package. An evaluation kit is also available to help
speed designs. For a similar device in a 10-pin µMAX
package with lower input voltage requirements (5.5V
max), refer to the MAX1692 data sheet.

Applications

Cellular Phones

Two-Way Radios and Walkie-Talkies

Computer Peripherals

Personal Communicators

PDAs and Handy-Terminals

Features

♦ Up to 96% Efficiency

♦ 1A Guaranteed Output Current

♦ 100% Duty Cycle in Dropout

♦ 2.7V to 14V Input Range (15V Absolute Max)

♦ ±1% Accurate Reference Output
♦ 0.24Ω P-Channel On-Resistance

♦ Synchronizable Switching Frequency

♦ Fixed-Frequency PWM Operation

300kHz (MAX1684)
600kHz (MAX1685)

♦ 150µA Normal-Mode Quiescent Current

♦ 25µA Low-Power Mode Quiescent Current

♦ 2µA Shutdown Current

♦ Dual Mode™ Fixed 3.3V (±1%) Output or

Adjustable Output (1.25V to V

IN

)

♦ Small 16-QSOP Package

♦ Auxiliary Output (CVL): 3V/5mA

MAX1684/MAX1685

Low-Noise, 14V Input, 1A, PWM

Step-Down Converters

MAX1684
MAX1685

LXIN

AIN

GND

OUTPUT

3.3V AT 1A

INPUT

2.7V TO 14V

BOOT

SHDN

CVH

CVL

STBY

SYNC/PWM

FB CC REF

+

+

19-1454; Rev 2; 7/01

PART

MAX1684EEE

MAX1685EEE

-40°C to +85°C

-40°C to +85°C

TEMP RANGE PIN-PACKAGE

16 QSOP

16 QSOP

EVALUATION KIT

AVAILABLE

Typical Operating Circuit

Ordering Information

Pin Configuration appears at end of data sheet.

Dual Mode is a trademark of Maxim Integrated Products, Inc.

________________________________________________________________ Maxim Integrated Products 1

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

MAX1684/MAX1685

Low-Noise, 14V Input, 1A, PWM
Step-Down Converters

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VIN= V

SHDN

= 6V, STBY = SYNC/PWM = CVL, V

BOOT

= V

OUT

, FB = AGND, circuit of Figure 1, TA= 0°C to +85°C, 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.

AIN to AGND ............................................................-0.3 to +15V

IN to PGND ................................................-0.3V to (V

AIN

+ 0.3V)

LX to PGND .................................................-0.5V to (V

IN

+ 0.3V)

PGND to AGND ..................................................................±0.3V

SHDN to AGND .........................................-0.3V to (V

AIN

+ 0.3V)

ILIM/SS, FB, CC, BOOT, REF to AGND ....-0.3V to (V

CVL

+ 0.3V)

CVH to IN..................................................................-6V to +0.3V

CVL, STBY, SYNC/PWM to AGND............................-0.3V to +6V

Reference Current ..............................................................±1mA

CVL Current .......................................................-1mA to +10mA

LX Peak Current (Internally Limited) .....................................2.3A

Continuous Power Dissipation (T

A

= +70°C)

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

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

VFB= V

OUT

, I

LOAD

= 0 to 1A

Low-power mode, STBY = low,
V

BOOT

= 3.3V (Note 2)

Normal mode, SYNC/PWM = low,
V

BOOT

= 3.3V (Note 2)

PWM mode,
SYNC/PWM = high,
V

BOOT

= 3.3V

(Note 2)

SYNC/PWM = high

Low-side switch, VIN= 2.7V, ILX= 200mA

High-side switch,
I

LX

= 1A

VFB= V

OUT

, I

LOAD

= 0 to 1A

VIN= 5V to 14V

BOOT = AGND (Note 1)

SYNC/PWM = low

VFB= 1.4V

CONDITIONS

0.14 0.27

Quiescent Power Consumption

0.9 2

25 65

mW

13 33

mA

20 80 130

Zero Crossing Threshold

-10 50 100

VV

FB

Feedback Voltage 1.238 1.251 1.264

V2.7 14Input Voltage Range

A0.15 0.4 0.9Current Limit, N-Channel

A1.2 1.75 2.3I

LIM

Current Limit in PWM Mode

Ω38On-Resistance, N-Channel

0.24 0.5

%0.01Output Load Regulation

A1Output Current Capability

VV

REF

V

IN

Output Adjust Range

nA-50 50I

FB

FB Input Current

UNITSMIN TYP MAXSYMBOLPARAMETER

FB = AGND, I

LOAD

= 0 to 1A VV

OUT

Output Voltage (3.3V Mode) 3.296 3.333 3.368

VIN= 6V

VIN= 2.7V

Ω

0.34 0.8

On-Resistance, P-Channel

MAX1684

MAX1685

MAX1684

MAX1685

SYNC/PWM = low mA285 380 475Pulse-Skipping Current Threshold

STBY = low

mA285 380 475I

LIMLP

Current Limit in Low-Power
Mode

MAX1684/MAX1685

Low-Noise, 14V Input, 1A, PWM

Step-Down Converters

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VIN= V

SHDN

= 6V, STBY = SYNC/PWM = CVL, V

BOOT

= V

OUT

, FB = AGND, circuit of Figure 1, TA= 0°C to +85°C, unless otherwise

noted. Typical values are at T

A

= +25°C.)

STBY = low, VIN= 2.7V

CONDITIONS

µA230 430

Quiescent Supply Current
in Dropout

UNITSMIN TYP MAXSYMBOLPARAMETER

SHDN = low

µA26Shutdown Supply Current

MAX1684 260 300 340

MAX1684 180 350

VIN= 14V, VLX= 0 or 14V, SHDN = low

SYNC Capture Range

MAX1685

kHz

520 600 680

f

OSC

Oscillator Frequency

µA20I

LX

LX Leakage Current

%100Maximum Duty Cycle

(Note 3) %

20

MAX1685

Constant-Frequency Minimum
Duty Cycle

10

-1µA < I

REF

< 50µA mV415Reference Load Regulation

VIN= 3V to 14V, BOOT = AGND,
I

CVL

= 0 to 5mA

V2.7 3.0 3.15

I

REF

= 0

CVL Regulator Output Voltage

2.7V < V

BOOT

< 5.5V mV0.2 5Reference Supply Regulation

V1.238 1.251 1.264V

REF

Reference Output Voltage

kHz

360 700

MAX1684

MAX1685

BOOT = AGND, I

CVL

= 5mA mV120CVL Dropout Voltage

Typical hysteresis is +10°C (Note 4) °C160Thermal Shutdown Threshold

BOOT falling edge,
typical hysteresis is 0.1V

V2.35 2.5 2.65BOOT Switchover Threshold

I

CVH

= -1mA V-5.0 -4.6 -4.1CVH with Respect to V

IN

SHDN, STBY, SYNC/PWM

V2V

IH

Logic Input High Voltage

V

ILIM/SS

= 1.4V µA3.3 4 4.65ILIM/SS Source Current

High or low period ns500SYNC/PWM Pulse Width

SHDN, STBY, SYNC/PWM

µA-1 1Logic Input Current

0.7V

IL

Logic Input Low Voltage

BOOT = AGND, CVL falling edge,
typical hysteresis is 40mV

V2.35 2.5 2.6

CVL Undervoltage Lockout
Threshold

V

MAX1684/MAX1685

Low-Noise, 14V Input, 1A, PWM
Step-Down Converters

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS

(VIN= V

SHDN

= 6V, STBY = SYNC/PWM = CVL, V

BOOT

= V

OUT

, FB = AGND, circuit of Figure 1, TA= -40°C to +85°C, unless other-

wise noted.) (Note 5)

Note 1: The output adjust range with BOOT connected to V

OUT

is V

REF

to 5.5V. Connect BOOT to AGND for V

OUT

> 5.5V.

Note 2: The quiescent power-consumption specifications include chip supply and gate-drive loss only. Divide these values by V

IN

(6V) to obtain quiescent currents. In normal and low-power modes, chip supply current dominates and quiescent power is
proportional to V

BOOT

(BOOT connected to OUT). In PWM mode, gate-drive loss dominates and quiescent power is propor-

tional to V

IN

✕

(VIN- V

CVH

). In addition, IR losses in power switches and external components typically increase PWM quies­cent power consumption by 5mW to 10mW. Note that if the device is not bootstrapped, additional power is dissipated in the
CVL linear regulator.

Note 3: When the duty factor (V

OUT

/ VIN) is less than this value, the switching frequency decreases in PWM mode to maintain

regulation.

Note 4: Thermal shutdown is disabled in low-power mode (STBY = low) to reduce power consumption.
Note 5: Specifications to -40°C are guaranteed by design, not production tested.

CVL Undervoltage Lockout
Threshold

2.4 2.6 V

BOOT = AGND, CVL falling edge,
typical hysteresis is 40mV

Logic Input Low Voltage V

IL

0.7

Logic Input High Voltage V

IH

2

V

SHDN, STBY, SYNC/PWM

ILIM/SS Source Current 3.1 4.7 µAV

ILIM/SS

= 1.4V

0.27

Normal mode, SYNC/PWM = low,
V

BOOT

= 3.3V (Note 2)

BOOT Switchover Threshold 2.35 2.65 VBOOT falling edge, typical hysteresis is 0.1V

CVH with Respect to V

IN

-5.0 -4.1 VI

CVH

= -1mA

CVL Regulator Output Voltage 2.7 3.15 V

VIN= 3V to 14V, BOOT = AGND,
I

CVL

= 0 to 5mA

Reference Output Voltage 1.232 1.268 VI

REF

= 0

Oscillator Frequency f

OSC

480 700

kHz

MAX1685

240 350MAX1684

Shutdown Supply Current 6 µA

SHDN = low

Quiescent Power Consumption

2

mW

Current Limit in Low-Power
Mode

I

LIMLP

285 475 mA

STBY = low

Output Voltage (3.3V Mode) V

OUT

3.280 3.382 V

PARAMETER SYMBOL MIN MAX UNITS

FB Input Current I

FB

-50 50 nA

Output Adjust Range V

REF

V

IN

V

Output Current Capability 1 A

Input Voltage Range 2.7 14 V

Output Feedback Voltage V

FB

1.233 1.269 V

Current Limit in PWM Mode I

LIM

1.2 2.3 A

CONDITIONS

VFB= 1.4V

BOOT = AGND (Note 1)

VIN= 6V to 14V

FB = AGND, I

LOAD

= 0 to 1A

VFB= V

OUT

, I

LOAD

= 0 to 1A

Low-power mode, STBY = low,
V

BOOT

= 3.3V (Note 2)

MAX1684/MAX1685

Low-Noise, 14V Input, 1A, PWM

Step-Down Converters

_______________________________________________________________________________________ 5

Typical Operating Characteristics

(Circuit of Figure 1, TA = +25°C, unless otherwise noted.)

MAX1684

EFFICIENCY vs. LOAD CURRENT

= 3.3V, V

(V

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

IN

A

D

E

C

B

F

0.1 1 10 100 1000 10,000
LOAD CURRENT (mA)

= 1.8V, 2.5V)

OUT

A: V

= 2.5V LP MODE

OUT

= 1.8V LP MODE

B: V

OUT

= 2.5V NORM MODE

C: V

OUT

= 1.8V NORM MODE

D: V

OUT

= 2.5V PWM MODE

E: V

OUT

= 1.8V PWM MODE

F: V

OUT

MAX1684/85 toc01

EFFICIENCY (%)

100

90

80

B

70

60

50

40

30

20

10

0

0.1 1 10 100 1000 10,000

MAX1684

EFFICIENCY vs. LOAD CURRENT

= 5V)

(V

100

90

80

70

60

50

EFFICIENCY (%)

40

30

20

B

A

C

0.1 1 10 100 1000 10,000

OUT

E

F

A: VIN = 6V LP MODE
B: V

IN

C: V

IN

D: V

IN

E: V

IN

F: V

IN

LOAD CURRENT (mA)

E

= 9V LP MODE
= 12V LP MODE
= 6V NORMAL MODE
= 9V NORMAL MODE
= 12V NORMAL MODE

D

MAX1684/85 toc04

EFFICIENCY (%)

100

90

80

70

60

50

B

40

30

20

10

0

1 10010 1000 10,000

MAX1685

EFFICIENCY vs. LOAD CURRENT

= 3.3V)

(V

100

90

A

80

70

B

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 1 10 100 1000 10,000

OUT

A: VIN = 4V LP MODE

= 12V LP MODE

B: V

IN

= 4V NORMAL MODE

C: V

IN

= 12V NORMAL MODE

D: V

IN

LOAD CURRENT (mA)

C

D

MAX1684/85 toc07

EFFICIENCY (%)

100

90

80

70

60

50

40

30

20

10

0

1 10010 1000 10,000

EFFICIENCY vs. LOAD CURRENT

A

EFFICIENCY vs. LOAD CURRENT

EFFICIENCY vs. LOAD CURRENT

VIN = 6V

MAX1684

(V

OUT

A: VIN = 4V LP MODE
B: V
C: V
D: V

LOAD CURRENT (mA)

MAX1684

= 5V, PWM MODE)

(V

OUT

A

LOAD CURRENT (mA)

MAX1685

= 5V PWM MODE)

(V

OUT

VIN =12V

LOAD CURRENT (mA)

= 3.3V)

= 12V LP MODE

IN

= 4V NORMAL MODE

IN

= 12V NORMAL MODE

IN

C

A: VIN = 6V
B: V
C: V

VIN = 9V

D

IN
IN

= 9V
=12V

C

MAX1684/85 toc02

EFFICIENCY (%)

MAX1684/85 toc05

EFFICIENCY (%)

MAX1684/85 toc08

EFFICIENCY (%)

EFFICIENCY vs. LOAD CURRENT

MAX1684

= 3.3V, PWM MODE)

(V

100

90

80

70

60

50

40

30

20

10

0

OUT

A

B

1 10010 1000 10,000

LOAD CURRENT (mA)

C

D

A: VIN = 4V
B: V
C: V
D: V

MAX1685

EFFICIENCY vs. LOAD CURRENT

= 3.3V, PWM MODE)

(V

100

90

80

70

60

50

40

30

20

10

0

OUT

VIN = 4V

VIN = 5V

VIN = 9V

VIN = 12V

1 10010 1000 10,000

LOAD CURRENT (mA)

MAX1685

EFFICIENCY vs. LOAD CURRENT

= 5V)

(V

100

90

80

70

60

50

40

30

20

10

A

0

0.1 1 10 100 1000 10,000

OUT

B

C

A: VIN = 6V LP MODE
B: V

IN

C: V

IN

D: V

IN

E: V

IN

F: V

IN

LOAD CURRENT (mA)

E

F

= 9V LP MODE
= 12V LP MODE

= 6V NORMAL MODE
= 9V NORMAL MODE
=12V NORMAL MODE

IN
IN
IN

= 5V
= 9V
= 12V

D

MAX1684/85 toc03

MAX1684/85 toc06

MAX1684/85 toc09