MAXIM MAX1843 Technical data

MAX1843

2.7A, 1MHz, Low-Voltage, Step-Down Regulator with
Internal Synchronous Rectification in QFN Package

________________________________________________________________ Maxim Integrated Products 1

19-1986; Rev 1; 3/02

General Description

The MAX1843 constant-off-time, pulse-width modulated
(PWM) step-down DC-DC converter is ideal for use in 5V
and 3.3V to low-voltage conversion necessary in note­book and subnotebook computers. This device features
an internal PMOS power switch and internal synchronous
rectification for high efficiency and reduced component
count. An external Schottky diode is not required. The
internal 90mΩ power switch and 70mΩ NMOS synchro­nous-rectifier switch easily deliver continuous load cur­rents up to 2.7A. The MAX1843 produces a preset +2.5V,
+1.8V, or +1.5V output voltage or an adjustable output
from +1.1V to VIN. It achieves efficiencies as high as
95%.

The MAX1843 uses a unique current-mode, constant-off­time, PWM control scheme, which includes Idle Mode™
to maintain high efficiency during light-load operation.
The programmable constant-off-time architecture sets
switching frequencies up to 1MHz, allowing the user to
optimize performance trade-offs between efficiency, out­put switching noise, component size, and cost. The
MAX1843 features an adjustable soft-start to limit surge
currents during startup, a 100% duty-cycle mode for low
dropout operation, and a low-power shutdown mode that
disconnects the input from the output and reduces sup­ply current below 1µA. The MAX1843 is available in a 28­pin QFN package with an exposed backside pad.

Applications

5V or 3.3V to Low-Voltage Conversion
CPU I/O Ring
Chipset Supplies
Notebook and Subnotebook Computers

Features

♦ ±1% Output Accuracy

♦ Up to 1MHz Switching Frequency

♦ 95% Efficiency

♦ Internal PMOS/NMOS Switches

90mΩ/70mΩ On-Resistance at V

IN

= +4.5V

110mΩ/80mΩ On-Resistance at V

IN

= +3V

♦ Output Voltage

+2.5V, +1.8V, or +1.5V Pin Selectable
+1.1V to V

IN

Adjustable

♦ +3V to +5.5V Input Voltage Range

♦ 350µA Operating Supply Current

♦ <1µA Shutdown Supply Current

♦ Programmable Constant-Off-Time Operation

♦ 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

♦ 28-Pin QFN Package

PART TEMP RANGE PIN-PACKAGE

Ordering Information

Idle Mode is a trademark of Maxim Integrated Products.

EVALUATION KIT

AVAILABLE

MAX1843EGI -40°C to +85°C 28 QFN

MAX1843

2526

27

28 22

2324

8

9

10 11 12 13 14

15

16

17

18

19

20

21

1

2

3

4

5

6

7

REF

TOFF

FB

N.C.

N.C.

N.C.

GND

N.C.

N.C.

N.C.

LX

N.C.

LX

LX

IN

SS

COMP

IN

N.C.

LX

LX

PGND

V

CC

FBSEL

PGND

PGND

QFN

TOP VIEW

N.C.

SHDN

Pin Configuration

TOFF

COMP

V

CC

FBSEL

SHDN

IN

PGND

GND

REF

SS

LX

FB

MAX1843

OUTPUT
+1.1V TO
V

IN

INPUT

+3V TO

+5.5V

0.01µF

1µF

2.2µF

470pF

10Ω

Typical Configuration

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.

查询MAX1843供应商

MAX1843

2.7A, 1MHz, Low-Voltage, Step-Down Regulator with
Internal Synchronous Rectification in QFN Package

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

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

CC

+ 0.3V)

LX Current (Note 1).............................................................±4.7A

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

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

Continuous Power Dissipation (T

A

= +70°C)
28-Pin QFN (derate 20mW/°C above +70°C, part mounted
on 1in

2

of 1oz copper)......................................................1.6W

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

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

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

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

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.

Input Voltage VIN, V

Preset Output Voltage V

Adjustable Output Voltage
Range

AC Load Regulation Error 2%

DC Load Regulation Error 0.4 %

Dropout Voltage V

Reference Voltage V

Reference Load Regulation ∆V

PMOS Switch On-Resistance R

NMOS Switch On-Resistance R

Current-Limit Threshold I

RMS LX Output Current 3.1 A

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

CC

TA = +25°C
to +85°C

CC

TA = 0°C to
+85°C

TA = +25°C
to +85°C

= 0°C to

T

A

+85°C

TA = +25°C
to +85°C

T

= 0°C to

A

+85°C

TA = +25°C
to +85°C

T

= 0°C to

A

+85°C

= 1A 250 mV

VIN = +4.5V 90 200

V

= +3V 110 250

IN

VIN = +4.5V 70 150

V

= +3V 80 200

IN

OUT

DO

REF

REFIREF

ON,P

ON,NILX

LIMIT

FBSEL = V
VIN =
+3V to
+5.5V

FBSEL =

unconnected

=

I

LOAD

0 to 2.5A

=

V

FB

V

OUT

V

= VCC = +3V to +5.5V, FBSEL = GND V

IN

VIN = VCC = +3V, I

TA = +25°C to +85°C 1.089 1.100 1.111

TA = 0°C to +85°C 1.084 1.100 1.117

= -1µA to +10µA 0.5 2 mV

ILX = 0.5A

= 0.5A

FBSEL = REF

FBSEL = GND

LOAD

3.0 5.5 V

2.500 2.525 2.550

2.487 2.525 2.563

1.500 1.515 1.530

1.492 1.515 1.538

1.800 1.818 1.836

1.791 1.818 1.845

1.089 1.100 1.111

1.084 1.100 1.117

REF

3.1 3.6 4.1 A

V

IN

V

V

V

mΩ

mΩ

MAX1843

2.7A, 1MHz, Low-Voltage, Step-Down Regulator with
Internal Synchronous Rectification in QFN Package

_______________________________________________________________________________________ 3

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 3)

PARAMETER

CONDITIONS MIN MAX

UNITS

Input Voltage

3.0 5.5 V

FBS E L = V

C C

2.475 2.756

FBS E L = unconnected 1.485 1.545

FBS E L = RE F 1.782 1.854

Preset Output Voltage V

OUT

I

LOAD

= 0 to 2.5A,

V

FB

= V

OU T

FBS E L = GN D 1.078 1.122

V

Adjustable Output Voltage
Range

V

IN

= VCC = +3V to +5.5V, FBS E L = GN D V

REF

V

IN

V

Reference Voltage V

REF

1.078 1.122 V

VIN = +4.5V 200

PMOS Switch On-Resistance R

ON,P

ILX = 0.5A

V

IN

= +3V 250

mΩ

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.)

Idle-Mode Current Threshold 0.3 0.6 0.9 A

Switching Frequency f (Note 2) 1 MHz

No-Load Supply Current IIN + I

Shutdown Supply Current

Thermal Shutdown Threshold T

Undervoltage Lockout

FB Input Bias Current V

Off-Time t

Off-Time Startup Period FB = GND 4 t

On-Time t

SS Source Current I

SS Sink Current I

SHDN Input Current I
SHD N Log i c Inp ut Low V ol tag e
SHD N Log i c Inp ut H i g h V ol tag e

FBSEL Input Current I

FBSEL Logic Thresholds

M axi m um O utp ut RM S C ur r ent 3.1 A

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

= 1.2V 350 600 µA

SHDN = GND, includes PMOS leakage <1 15 µA

Hysteresis = 15°C 160 °C

V

falling, hysteresis = 90mV 2.5 2.6 2.7 V

IN

= 1.2V 0 60 250 nA

FB

R

= 110kΩ 0.9 1.00 1.1

TOFF

R

= 30.1kΩ 0.24 0.30 0.37

TOFF

R

= 499kΩ 3.8 4.5 5.2

TOFF

OFF

(Note 2) 0.4 µs

456µA

VSS = 1V 100 µA

V

SHDN

= 0 to V

CC

-1 1 µA

0.8 V

2.0 V

V

FBSEL

= 0 to V

CC

-4 4 µA

I

IN

V

SHDN

UVLO

SHDN

CCVFB

+ I

CC

OFF

ON

SS

SS

IL

V

IH

V

FB

FBSEL = GND 0.2

FBSEL = REF 0.9 1.3

FBSEL = unconnected

FBSEL = V

CC

0.7V

- 0.2

V

- 0.2

CC

CC

0.7V
+ 0.2

CC

µs

µs

V

RMS

SYMBOL

VIN, V

CC

V

= +3V to + 5.5V,

IN

Typical Operating Characteristics

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

0.001 0.01 0.1 1 10

EFFICIENCY vs. OUTPUT CURRENT

(V

IN

= +5.0V, L = 2.5µH)

MAX1843 toc03

OUTPUT CURRENT (A)

V

OUT

= +1.5V, R

TOFF

= 1OOkΩ,

f

PWM

= 770kHz

V

OUT

= +1.8V, R

TOFF

= 75kΩ,

f

PWM

= 910kHz

V

OUT

= +2.5V, R

TOFF

= 47kΩ,

f

PWM

= 1070kHz

100

95

90

85

80

70

65

60

55

50

75

EFFICIENCY (%)

0.001 0.01 0.1 1 10

EFFICIENCY vs. OUTPUT CURRENT

(V

IN

= +3.3V, L = 1.5µH)

MAX1843 toc04

OUTPUT CURRENT (A)

V

OUT

= +2.5V, R

TOFF

= 56kΩ,

f

PWM

= 1000kHz

V

OUT

= +2.5V, R

TOFF

= 39kΩ,

f

PWM

= 610kHz

V

OUT

= +1.8V, R

TOFF

= 43kΩ,

f

PWM

= 1050kHz

100

95

90

85

80

70

65

60

55

50

75

EFFICIENCY (%)

0.001 0.01 0.1 1 10

EFFICIENCY vs. OUTPUT CURRENT

(f

PWM

= 270kHz)

MAX1843 toc05

I

OUT

(A)

VIN = +3.3V, V

OUT

= +1.8V,

L = 4.7µH, R

TOFF

= 160kΩ

100

95

90

85

80

70

65

60

55

50

75

EFFICIENCY (%)

VIN = +5V, V

OUT

= +1.8V, L = 5.6µH,

R

TOFF

= 240kΩ

NORMALIZED OUTPUT ERROR

vs. OUTPUT CURRENT

MAX1843 toc06

0.001 0.01 0.1 1 10
OUTPUT CURRENT (A)

VIN = +3.3V, V

OUT

= +1.5V, L = 1.5µH

VIN = +5V, V

OUT

= +1.5V, L = 2.5µH

0.1

0

-0.1

-0.2

-0.3

-0.4

NORMALIZED OUTPUT ERROR (%)

PARAMETER

CONDITIONS MIN MAX

V

IN

= +4.5V 150

NMOS Switch On-Resistance R

ON,NILX

= 0.5A

V

IN

= +3V 200

mΩ

Current-Limit Threshold I

LIMIT

2.9 4.3 A

Idle-Mode Current Threshold 0.2 1.0 A

No-Load Supply Current

VFB = 1.2V 600 µA

FB Input Bias Current I

FB

VFB = 1.2V 0 300 nA

Off-Time t

OFF

R

TOFF

= 110kΩ 0.85 1.15 µs

MAX1843

2.7A, 1MHz, Low-Voltage, Step-Down Regulator with
Internal Synchronous Rectification in QFN Package

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(VIN= VCC= +3.3V, FBSEL = GND, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 3)

Note 2: Recommended operating frequency, not production tested.
Note 3: Specifications from 0°C to -40°C are guaranteed by design, not production tested.

SYMBOL

IIN + I

CC

UNITS

MAX1843

2.7A, 1MHz, Low-Voltage, Step-Down Regulator with
Internal Synchronous Rectification in QFN Package

_______________________________________________________________________________________ 5

Typical Operating Characteristics (continued)

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

0

1.0

0.5

2.0

1.5

3.0

2.5

3.5

4.5

4.0

5.0

0 100 150 20050 250 300 350 450400 500

OFF-TIME vs. R

TOFF

MAX1843 toc02

R

TOFF

(kΩ)

t

OFF

(µs)

LOAD-TRANSIENT RESPONSE

V

OUTPUT

50mV/div

I

L

2A/div

MAX1843 toc09

10µs/div

0

LINE-TRANSIENT RESPONSE

V

INPUT

2V/div

V

OUTPUT

20mV/div
AC-COUPLED

MAX1843 toc10

20µs/div

I

OUT

= 2.5A, V

OUT

= +1.5V

R

TOFF

= 100kΩ, L = 2.2µH

0

400

200

800

600

1000

1200

0 1.0 1.50.5 2.0 2.5 3.0

SWITCHING FREQUENCY

vs. OUTPUT CURRENT

MAX1843 toc07

OUTPUT CURRENT (A)

FREQUENCY (kHz)

VIN = +5V, V

OUT

= +2.5V, L = 2.5µH

VIN = +3.3V, V

OUT

= +1.5V, L = 1.5µH

VIN = +5V, V

OUT

= +1.5V, L = 2.5µH

0

0

0

0

STARTUP AND SHUTDOWN

V

SS

2V/div

MAX1843 toc08

V

SHDN

5V/div

R

OUT

= 0.5Ω, R

TOFF

= 56kΩ

V

IN

= +3.3V, V

OUT

= +1.5V

I

INPUT

1A/div

V

OUTPUT

1V/div

1ms/div

500

450

(µA)

CC

400

+ I

IN

350

300

250

200

150

100

NO-LOAD SUPPLY CURRENT, I

50

0

021 3456

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

NO LOAD

SHUTDOWN

VIN (V)

MAX1843 toc01

100

(nA)

90

CC

80

+ I

IN

70

60

50

40

30

20

10

SHUTDOWN SUPPLY CURRENT, I

0