Rainbow Electronics MAX1623 User Manual

MAX1623

3A, Low-Voltage, Step-Down Regulator with

Synchronous Rectification and Internal Switches

________________________________________________________________ Maxim Integrated Products 1

EVALUATION KIT MANUAL

AVAILABLE

General Description

The MAX1623 switch-mode buck regulator with syn­chronous rectification provides local CPU and bus-ter­mination power in notebook and desktop computers.
An internal 55mΩ (typ), 3A PMOS power switch and
60mΩ (typ), 3A NMOS synchronous-rectifier switch
deliver continuous load currents up to 3A from a 5V
supply with 95% typical efficiency. Output accuracy is
±1%, including line and load regulation.

The MAX1623 features constant-off-time, current-mode
pulse-width-modulation (PWM) control with switching
frequencies as high as 350kHz. An external resistor at
the TOFF pin sets the off-time, allowing optimum design
flexibility in terms of switching frequency, output switch­ing noise, and inductor size. This device is available in
a space-saving 20-pin SSOP package.

________________________Applications

5V to 3.3V Conversion

Notebook Computer CPU I/O Supply

Desktop Computer Bus-Termination Supply

CPU Daughter Card Supply

DSP Supply

____________________________Features

♦ ±1% Output Accuracy, Including Line and Load

Regulation

♦ 94% Efficiency

♦ Internal Switches

55mΩ PMOS Power Switch
60mΩ NMOS Synchronous-Rectifier Switch

♦ Guaranteed 3A Load Capability

♦ Minimal External Components

♦ Pin-Selectable Fixed 3.3V, 2.5V, or

Adjustable (1.1V to 3.8V) Output Voltage

♦ 4.5V to 5.5V Input Voltage Range

♦ 400µA (typ) Supply Current

♦ <1µA Shutdown Supply Current

♦ Constant-Off-Time PWM Operation

♦ Switching Frequencies Up to 350kHz

♦ Idle Mode™ Operation at Light Loads

♦ Thermal Shutdown Protection
♦ Available in 20-Pin SSOP

20

19

18

17

16

15

14

13

1

2

3

4

5

6

7

8

LX

PGND

LX

PGND

IN

LX

IN

LX

TOP VIEW

LX

PGND

V

CC

COMPFBSEL

IN

LX

12

11

9

10

REF

GNDFB

TOFF

MAX1623

SSOP

SHDN

Pin Configuration

5V

INPUT

MAX1623

2.5V

OUTPUT

IN LX

PGND

GND

FB

REFCOMP

FBSEL

V

CC

TOFF

SHDN

Typical Operating Circuit

19-1436; Rev 2; 3/02

PART

MAX1623EAP -40°C to +85°C

TEMP RANGE PIN-PACKAGE

20 SSOP

Ordering Information

Idle Mode is a trademark of Maxim Integrated Products.

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.

MAX1623

3A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VIN= VCC= 5V, FBSEL unconnected, R

TOFF

= 110kΩ, 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.

IN to PGND .....................................................................0V to 6V

V

CC

to GND ................................................................-0.3V to 6V

PGND to GND.....................................................................±0.5V

IN to V

CC

.............................................................................±0.5V

LX Current (Note 1).............................................................±5.5A

SHDN to GND .............................................................-0.3V to 6V

REF, FBSEL, COMP, FB, TOFF to GND .....-0.3V to (V

CC

+ 0.3V)

REF Short to GND ......................................................Continuous

Continuous Power Dissipation (T

A

= +70°C) (with part mounted
on 1 sq. inch of one ounce copper)

20-Pin SSOP (derate 22mW/°C above +70°C) ................1.3W

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

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

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

SHDN = GND or V

CC

FBSEL = REF

FBSEL = GND

VIN= 4.5V to 5.5V,
I

LOAD

= 0 to 3A

(Note 2)

FBSEL = GND, adjustable output mode, VFB= 1.2V

VCCfalling, 100mV hysteresis

I

LOAD

≥ 1.5A (Note 2)

VIN= 4.5V

SHDN = GND

VIN= 4.5V

FBSEL = GND or REF (Note 2)

I

REF

= 0

Does not include switching losses

I

REF

= -1µA to 10µA

CONDITIONS

V0.8

SHDN Input Low Voltage

µA-1 0.03 1

SHDN Input Current

2

%

1

AC Output Load Regulation

µs0.85 1.00 1.15Off-Time Default Period

µs0.5 4Off-Time Adjustment Range

kHz500Error-Amplifier Gain Bandwidth

nA-25 25FB Input Bias Current

V4.1 4.2 4.3Undervoltage Lockout Threshold

°C145Thermal Shutdown Threshold

µA0.5 10Shutdown Supply Current

µA400 525No-Load Supply Current

A1 1.25 1.5Idle Mode Threshold (Note 3)

2.49 2.525 2.550

V

3.296 3.330 3.366

V4.5 5.5Input Voltage Range

Output Voltage

kHz350Maximum Switching Frequency

mΩ60 100NMOS Switch On-Resistance

mΩ55 100PMOS Switch On-Resistance

A3.65 4.65Current-Limit Threshold

1.089 1.100 1.110

VV

REF

3.80Output Adjustment Range

V1.089 1.100 1.110Reference Output Voltage

mV1Reference Load Regulation

UNITSMIN TYP MAXPARAMETER

FBSEL = unconnected

FBSEL = V

CC

FBSEL = GND or REF

V2

SHDN Input High Voltage

VIN= 5.5V, VLX= 5.5V or 0 µA±20LX Leakage Current

A3.65RMS LX Output Current

Note 1: LX has internal clamp diodes to PGND and IN. Applications that forward bias these diodes should take care not to exceed

the IC’s package power dissipation limits.

MAX1623

_______________________________________________________________________________________ 3

3A, Low-Voltage, Step-Down Regulator with

Synchronous Rectification and Internal Switches

ELECTRICAL CHARACTERISTICS

(VIN= VCC= 5V, FBSEL unconnected, R

TOFF

= 110kΩ, TA= -40°C to +85°C, unless otherwise noted.) (Note 4)

Note 2: Guaranteed by design, not production tested.
Note 3: Idle Mode threshold is defined as the transition point in the load-current range between Idle Mode and constant-off-time

operation.

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

SHDN = GND or V

CC

VIN= 4.5V to 5.5V,
I

LOAD

= 0 to 3A

FBSEL = GND, adjustable output mode, VFB= 1.2V

VCCfalling, 100mV hysteresis

VIN= 4.5V

VIN= 5.5V, VLX= 5.5V or 0

SHDN = GND

VIN= 4.5V

V

FBSEL = GND or REF (Note 2)

I

REF

= 0

Does not include switching losses

CONDITIONS

V0.8

FBSEL = unconnected

SHDN Input Low Voltage

µA-1 1

FBSEL = V

CC

SHDN Input Current

FBSEL = GND or REF

2.2

SHDN Input High Voltage

µs0.85 1.25Off-Time Default Period

µs0.55 4Off-Time Adjustment Range

nA-50 50FB Input Bias Current

V4.0 4.3Undervoltage Lockout Threshold

µA-20 20LX Leakage Current

µA10Shutdown Supply Current

µA600No-Load Supply Current

2.450 2.550

V

3.234 3.366

V4.5 5.5Input Voltage Range

Output Voltage

Ω

0.1NMOS Switch On-Resistance

Ω

0.1PMOS Switch On-Resistance

A3.5 4.75Current-Limit Threshold

1.075 1.110

VV

REF

3.8Output Adjustment Range

V1.075 1.110Reference Output Voltage

UNITSMIN TYP MAXPARAMETER

MAX1623

3A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches

4 _______________________________________________________________________________________

__________________________________________Typical Operating Characteristics

(Circuit of Figure 2, TA = +25°C, unless otherwise noted.)

100

0

0.001 0.1 10.01 10

EFFICIENCY

vs. OUTPUT CURRENT

20

MAX1623 TOC01

OUTPUT CURRENT (A)

EFFICIENCY (%)

40

60

80

90

10

30

50

70

V

OUT

= 3.3V, R

TOFF

= 110kΩ

V

OUT

= 1.1V, R

TOFF

= 280kΩ

V

OUT

= 2.5V, R

TOFF

= 180kΩ

0

1

3

2

4

5

0 200100 300 400 500 600

SWITCH OFF-TIME

vs. OFF-TIME RESISTANCE

MAX1623 TOC02

R

TOFF

(kΩ)

t

OFF

(µs)

1000

100

10

1

0.1

0.01
0123

4

56

SUPPLY CURRENT

vs. INPUT VOLTAGE

MAX1623 TOC03

INPUT VOLTAGE (V)

SUPPLY CURRENT (µA)

SHDN = IN

SHDN = GND

0

150

50

100

250

200

350

300

0 1000 1500500 2000 2500 3000

SWITCHING FREQUENCY

vs. LOAD CURRENT

MAX1623 TOC04

LOAD CURRENT (mA)

SWITCHING FREQUENCY (kHz)

V

OUT

= 2.5V, R

TOFF

= 180kΩ

V

OUT

= 3.3V, R

TOFF

= 110kΩ

V

OUT

= 1.1V, R

TOFF

= 280kΩ

0

200

150

100

50

300

250

350

400

4.5 4.94.7 5.1 5.3 5.5

SWITCHING FREQUENCY

vs. INPUT VOLTAGE

MAX1623 TOC05

INPUT VOLTAGE (V)

SWITCHING FREQUENCY (kHz)

VIN = 5V, V

OUT

= 3.3V,

R

TOFF

= 110kΩ

VIN = 5V, V

OUT

= 2.5V,

R

TOFF

= 180kΩ

0

-0.50

0.10.01 10.001 10

LOAD REGULATION ERROR

vs. LOAD CURRENT

-0.40

MAX1623 TOC07

LOAD CURRENT (A)

LOAD REGULATION ERROR (%)

-0.30

-0.20

-0.10

-0.35

-0.45

-0.25

-0.15

-0.05

V

OUT

= 2.5V, R

TOFF

= 180kΩ

V

OUT

= 3.3V, R

TOFF

= 110kΩ

-0.01

-0.02

-0.03

-0.04

-0.05

-0.06

0

0 5 10 15 20 25

REFERENCE LOAD REGULATION ERROR

vs. REFERENCE LOAD CURRENT

MAX1623 TOC06

REFERENCE LOAD CURRENT (µA)

REFERENCE LOAD REGULATION ERROR (%)

TA = +25°C

T

A

= -40°C

T

A

= +85°C