Maxim MAX1644EAE Datasheet

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General Description

The MAX1644 constant-off-time, PWM step-down DC­DC converter is ideal for use in applications such as PC
cards, CPU daughter cards, and desktop computer
bus-termination boards. The device features internal
synchronous rectification for high efficiency and
reduced component count. It requires no external
Schottky diode. The internal 0.10Ω PMOS power switch
and 0.10Ω NMOS synchronous-rectifier switch easily
deliver continuous load currents up to 2A. The
MAX1644 produces a preset +3.3V or +2.5V output
voltage or an adjustable output from +1.1V to VIN. It
achieves efficiencies as high as 95%.

The MAX1644 uses a unique current-mode, constant­off-time, PWM control scheme, which includes an Idle
Mode™ to maintain high efficiency during light-load
operation. The programmable constant-off-time archi­tecture sets switching frequencies up to 350kHz, allow­ing the user to optimize performance trade-offs
between efficiency, output switching noise, component
size, and cost. The device also features an adjustable
soft-start to limit surge currents during start-up, a 100%
duty cycle mode for low-dropout operation, and a low­power shutdown mode that disconnects the input from
the output and reduces supply current below 1µA. The
MAX1644 is available in a 16-pin SSOP package.

Applications

+5V to +3.3V/+2.5V Conversion
CPU I/O Supply
+3.3V PC Card and CardBus Applications
Notebook and Subnotebook Computers
Desktop Bus-Termination Boards
CPU Daughter Card Supply

Features

♦ ±1% Output Accuracy
♦ 95% Efficiency
♦ Internal PMOS and NMOS Switches

70mΩ On-Resistance at V

IN

= +4.5V

100mΩ On-Resistance at VIN= +3V

♦ Output Voltage

+3.3V or +2.5V Pin-Selectable
+1.1V to VINAdjustable

♦ +3V to +5.5V Input Voltage Range
♦ 360µA (max) Operating Supply Current
♦ < 1µA Shutdown Supply Current
♦ Programmable Constant-Off-Time Operation
♦ 350kHz (max) Switching Frequency
♦ Idle Mode Operation at Light Loads
♦ Thermal Shutdown
♦ Adjustable Soft-Start Inrush Current Limiting
♦ 100% Duty Cycle During Low-Dropout Operation
♦ Output Short-Circuit Protection
♦ 16-Pin SSOP Package

MAX1644

2A, Low-V oltage, Step-Down Regulator with

Synchronous Rectification and Internal Switches

________________________________________________________________

Maxim Integrated Products

1

16
15
14
13
12
11
10

9

1
2
3
4
5
6
7
8

SHDN LX

PGND
LX
PGND
V

CC

FBSEL
REF
GND

TOP VIEW

MAX1644

SSOP

IN

LX

COMP

IN

SS

TOFF

FB

19-1457; Rev 0; 5/99

PART

MAX1644EAE -40°C to +85°C

TEMP. RANGE PIN-PACKAGE

16 SSOP

EVALUATION KIT MANUAL

FOLLOWS DATA SHEET

Pin Configuration

Ordering Information

Idle Mode is a trademark of Maxim Integrated Products.

Typical Operating Circuit

TOFF

COMP

V

CC

FBSEL
SHDN

IN

PGND

GND

REF

SS

LX
FB

MAX1644

R

TOFF

OUTPUT
+1.1V TO
V

IN

INPUT

+3V TO

+5.5V

MAX1644

2A, Low-V oltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VIN= VCC= +3.3V, FBSEL = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +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.

VCC, IN to GND ........................................................-0.3V to +6V

IN to V

CC

.............................................................................±0.3V

GND to PGND.....................................................................±0.3V

LX to PGND .................................................-0.3V to (V

IN

+ 0.3V)

All Other Pins to GND.................................-0.3V to (V

CC

+ 0.3V)

Continuous LX Output Current..............................................2.5A

REF Short Circuit to GND Duration ............................Continuous

ESD Protection.....................................................................±2kV

Continuous Power Dissipation (T

A

= +70°C)
SSOP (derate 16.7mW/°C above +70°C;
part mounted on 1 in.

2

of 1oz. copper)............................1.2W

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

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

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

Hysteresis = 15°C

SHDN = GND

SHDN = GND

I

LOAD

= 0 to 2A,

VFB= V

OUT

VFB= 1.2V

(Note 1)

VIN= VCC= 3V, I

LOAD

= 1A, FBSEL = V

CC

ILX= 0.5A

FBSEL = REF, VCC, or unconnected

VIN= VCC= 3V to 5.5V,
I

LOAD

= 0, FBSEL = GND or REF

FBSEL = GND

I

REF

= -1µA to +10µA

CONDITIONS

°C150T

SHDN

Thermal Shutdown
Threshold

µA15I

IN

PMOS Switch Off-Leakage
Current

µA<1 3I

CC(SHDN)

Shutdown Supply Current

µA240 360IIN+ I

CC

No-Load Supply Current

kHz350fSwitching Frequency

A0.25 0.45 0.65I

IM

Idle Mode Current
Threshold

A2.5 2.9 3.3I

LIMIT

Current-Limit Threshold

mΩ

100 200

R

ON, P

PMOS Switch
On-Resistance

70 150

mV0.5 1∆V

REF

Reference Load Regulation

2.500 2.525 2.550 V

3.300 3.333 3.366

V3.0 5.5VIN, V

CC

Input Voltage

V1.089 1.100 1.111V

REF

Reference Voltage

mV200V

DO

Dropout Voltage

%

0.4

1.089 1.100 1.111

V

OUT

Preset Output Voltage

Adjustable Output Voltage
Range

VV

REF

V

IN

0.2

DC Load Regulation Error

UNITSMIN TYP MAXSYMBOLPARAMETER

VIN= VCC= 4V to 5.5V,
FBSEL = unconnected

VIN= VCC= 3V to 5.5V,
FBSEL = V

CC

VIN= VCC= 3V to 5.5V,
FBSEL = REF

VIN= 4.5V
VIN= 3V

ILX= 0.5A mΩ

100 200

R

ON, N

NMOS Switch
On-Resistance

70 150VIN= 4.5V

VIN= 3V

FBSEL = GND
FBSEL = REF, VCC, or unconnected

1

AC Load Regulation Error %

2

MAX1644

2A, Low-V oltage, Step-Down Regulator with

Synchronous Rectification and Internal Switches

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VIN= VCC= +3.3V, FBSEL = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

ELECTRICAL CHARACTERISTICS

(VIN= VCC= +3.3V, FBSEL = GND, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 2)

Note 1: Recommended operating frequency, not production tested.
Note 2: Specifications from 0°C to -40°C are guaranteed by design, not production tested.

R

TOFF

= 150kΩ

VFB= 1.2V

VFB= 1.2V

ILX= 0.5A

VIN= 3.0V to 5.5V, I

LOAD

= 0,

FBSEL = GND or REF

ILX= 0.5A

CONDITIONS

µs1.03 1.63t

OFF

Off-Time Default Period

nA0 250I

FB

FB Input Bias Current

µA360IIN+ I

CC

No-Load Supply Current

A0.2 0.7I

IM

Idle Mode Current
Threshold

A2.3 3.5I

LIMIT

Current-Limit Threshold

mΩ

200

R

ON, P

PMOS Switch
On-Resistance

mΩ

150

200

R

ON, N

2.48 2.57

3.276 3.390

V3.0 5.5V

IN

Input Voltage

V1.08 1.12V

REF

Reference Voltage

VV

REF

V

IN

Adjustable Output Voltage

1.08 1.12

UNITSMIN TYP MAXSYMBOLPARAMETER

VIN= VCC= 4V to 5.5V,
FBSEL = unconnected

VIN= 3V to 5.5V, FBSEL = V

CC

VIN= 3V to 5.5V, FBSEL = REF

VIN= 4.5V
VIN= 3V

NMOS Switch
On-Resistance

150VIN= 4.5V

VIN= 3V

0.7 · V

CC

0.7 · V

CC

- 0.2 + 0.2

FBSEL = unconnected

FBSEL Logic Thresholds

VCC- 0.2FBSEL = V

CC

SS Sink Current I

SS

100 µA

SHDN Input Current

I

SHDN

-0.5 0.5 µA

SS Source Current I

SS

3.5 5 6.5 µA

SHDN Input Low Threshold

V

IL

0.8 V

SHDN Input High Threshold

V

IH

2.0 V

FBSEL Input Current -5 +5 µA

0.2

V

0.9 1.3

VSS= 1V
V

SHDN

= 0 to V

CC

FBSEL = GND
FBSEL = REF

PARAMETER SYMBOL MIN TYP MAX UNITS

Undervoltage Lockout
Threshold

V

UVLO

2.5 2.6 2.7 V

FB Input Bias Current I

FB

0 80 200 nA

t

OFF

1.13 1.33 1.53

0.20 0.33

Off-Time Start-Up Period t

OFF

4 · t

OFF

µs

On-Time Period t

ON

0.4 µs

CONDITIONS

VFB= 1.2V
R

TOFF

= 150kΩ

R

TOFF

= 30.1kΩ

VINfalling, hysteresis = 40mV

FB = GND

Off-Time Default Period

4.3 5.6

µs

R

TOFF

= 499kΩ

V

I

LOAD

= 0 to 2A,

VFB= V

OUT

V

OUT

Preset Output Voltage

MAX1644

2A, Low-V oltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches

4 _______________________________________________________________________________________

Typical Operating Characteristics

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

110

0

10

30
20

40

50

70
60

80

90

100

0.001 0.01 0.1

EFFICIENCY vs. OUTPUT CURRENT

MAX1644-01

OUTPUT CURRENT (A)

EFFICIENCY (%)

VIN = 5V, V

OUT

= 3.3V,

L = 6.0µH, R

TOFF

= 120kΩ

100

110

0

10

30
20

40

50

70
60

80

90

0.001 0.01 0.1

EFFICIENCY vs. OUTPUT CURRENT

MAX1644-02

OUTPUT CURRENT (A)

EFFICIENCY (%)

VIN = 3.3V, V

OUT

= 1.5V,

L = 4.7µH, R

TOFF

= 200kΩ

VIN = 5V, V

OUT

= 1.5V,

L = 6.0µH, R

TOFF

= 270kΩ

110

-1.0

-0.9

-0.7

-0.8

-0.6

-0.5

-0.3

-0.4

-0.2

-0.1

0

0.0001 0.001 0.01 0.1

DC LOAD-REGULATION ERROR

vs. OUTPUT CURRENT

MAX1644-03

OUTPUT CURRENT (A)

DC LOAD-REGULATION ERROR (%)

A

B

E

C

D

A: V

IN

= 3.3V, V

OUT

= 1.5V, L = 4.7µH,

R

TOFF

= 200kΩ, FBSEL = GND

B: V

IN

= 3.3V, V

OUT

= 1.5V, L = 4.7µH,

R

TOFF

= 200kΩ, FBSEL = REF

C: V

IN

= 5V, V

OUT

= 3.3V, L = 6.0µH,

R

TOFF

= 120kΩ, FBSEL = OPEN

D: V

IN

= 5V, V

OUT

= 1.5V, L = 6.0µH,

R

TOFF

= 270kΩ, FBSEL = GND

E: V

IN

= 5V, V

OUT

= 1.5V, L = 6.0µH,

R

TOFF

= 270kΩ, FBSEL = REF

0

100

50

250

200

150

300

350

0 1.00.5 1.5 2.0

SWITCHING FREQUENCY

vs. OUTPUT CURRENT

MAX1644-04

OUTPUT CURRENT (A)

SWITCHING FREQUENCY (kHz)

VIN = 3.3V,
V

OUT

= 1.5V,
L = 4.7µH,
R

TOFF

= 200kΩ

VIN = 5V,
V

OUT

= 1.5V,
L = 6.0µH,
R

TOFF

= 270kΩ

VIN = 5V,
V

OUT

= 3.3V,
L = 6.0µH,
R

TOFF

= 120kΩ

0

150
100

50

200

250

300

350

400

450

500

021 3456

SUPPLY CURRENT vs. SUPPLY VOLTAGE

MAX1644-07

SUPPLY VOLTAGE

SUPPLY CURRENT I

CC

(µA)

0

0.03

0.02

0.01

0.04

0.05

0.06

0.07

0.08

0.09

0.10

SHUTDOWN SUPPLY CURRENT I

IN

+ I

CC

(µA)

I

OUT

= 0

UNDERVOLTAGE
LOCKOUT

SHDN = VIN = V

CC

SHDN = GND

0

1.0

0.5

2.5

2.0

1.5

4.0

3.5

3.0

4.5

0 200100 300 400 500 600

OFF-TIME vs. R

TOFF

MAX1644-06

R

TOFF

(kΩ)

t

OFF

(µs)

V

SHDN

5V/div

I

IN

1A/div

0

0

V

OUT

2V/div

V

SS

1V/div

0

0

2ms/div

START-UP AND

SHUTDOWN TRANSIENTS

MAX1644-09

VIN = 5.0V, V

OUT

= 3.3V, I

OUT

= 2A