Rainbow Electronics MAX1844 User Manual

General Description

The MAX1844 pulse-width modulation (PWM) controller
provides high efficiency, excellent transient response,
and high DC output accuracy needed for stepping
down high-voltage batteries to generate low-voltage
CPU core or chipset/RAM supplies in notebook com­puters.

Maxim’s proprietary Quick-PWM™ quick-response,
constant-on-time PWM control scheme handles wide
input/output voltage ratios with ease and provides
100ns “instant-on” response to load transients while
maintaining a relatively constant switching frequency.
Efficiency is enhanced by an ability to drive very large
synchronous-rectifier MOSFETs. Accurate current sens­ing to ensure reliable overload protection is available
using an external current-sense resistor in series with
the synchronous rectifier. Alternatively, the synchronous
rectifier itself can be used for less accurate current
sensing at the lowest possible power dissipation.

Single-stage buck conversion allows the MAX1844 to
directly step down high-voltage batteries for the highest
possible efficiency. Alternatively, two-stage conversion
(stepping down the 5V system supply instead of the
battery) at a higher switching frequency allows the mini­mum possible physical size.

The MAX1844 is intended for CPU core, chipset,
DRAM, or other low-voltage supplies as low as 1V. It is
available in 20-pin QSOP, and QFN packages and
includes both adjustable overvoltage and undervoltage
protection.

For a dual step-down PWM controller with accurate cur­rent limit, refer to the MAX1845. The MAX1714/ MAX1715
single/dual PWM controllers are similar to the MAX1844/
MAX1845 but do not use current-sense resistors.

Applications

Notebook Computers
CPU Core Supplies
Chipset/RAM Supplies as Low as 1V

1.8V and 2.5V Supplies

Features

♦ Ultra-High Efficiency
♦ Accurate Current-Limit Option
♦ Quick-PWM with 100ns Load-Step Response
♦ 1% V

OUT

Accuracy Over Line and Load

♦ 1.8V/2.5V Fixed or 1V to 5.5V Adjustable Output

Range

♦ 2V to 28V Battery Input Range
♦ 200/300/450/600kHz Switching Frequency
♦ Adjustable Overvoltage Protection
♦ Adjustable Undervoltage Protection
♦ 1.7ms Digital Soft-Start
♦ Drives Large Synchronous-Rectifier FETs
♦ 2V ±1% Reference Output
♦ Power-Good Window Comparator

MAX1844

High-Speed Step-Down Controller with

Accurate Current Limit for Notebook Computers

________________________________________________________________ Maxim Integrated Products 1

19-1993; Rev 1; 3/02

EVALUATION KIT

AVAILABLE

Pin Configuration appears at end of data sheet.

Quick-PWM is a trademark of Maxim Integrated Products.

V

CC

5V INPUT

BATTERY

4.5V TO 28V

OUTPUT

2.5V

SHDN

ILIM

DL

LX

V+

BST

DH

CS

OUT

SKIP

V

DD

MAX1844

UVP

REF

PGOOD
LATCH

OVP
FB

GND

Minimal Operating Circuit

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.

Ordering Information

PART TEMP RANGE PIN-PACKAGE

MAX1844EEP -40°C to +85°C 20 QSOP

MAX1844EGP -40°C to +85°C 20 QFN

MAX1844

High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

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.

V+ to GND..............................................................-0.3V to +28V

V

CC

, VDDto GND.....................................................-0.3V to +6V

OUT, PGOOD,

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

FB, ILIM, LATCH, OVP, REF, SKIP,

TON, UVP to GND..................................-0.3V to (V

CC

+ 0.3V)

BST to GND............................................................-0.3V to +34V

CS to GND.................................................................-6V to +30V

DL to GND..................................................-0.3V to (V

DD

+ 0.3V)

DH to LX.....................................................-0.3V to (BST + 0.3V)

LX to BST..................................................................-6V to +0.3V

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

Continuous Power Dissipation (T

A

= +70°C)

20-Pin QSOP (derate 9.1mW/°C above +70°C)...........727mW

20-Pin 5mm

✕

5mm QFN (derate 20.0mW/°C

above +70°C).................................................................1.60W

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

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, V+ = 15V, VCC= VDD= 5V, SKIP = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at
T

A

= +25°C.)

PARAMETER

CONDITIONS

MIN

TYP MAX

UNITS

Battery voltage, V+

2

28

Input Voltage Range

VCC , V

DD

4.5

5.5

V

0.99

1.01

2.5

Error Comparator Threshold
(DC Output Voltage Accuracy)
(Note 1)

V+ = 4.5V to 28V,
SKIP = V

CC

FB = V

CC

1.8

V

Load Regulation Error

I

LOAD

= 0 to 3A, SKIP = V

CC

9

mV

Line Regulation Error

VCC = 4.5V to 5.5V, V+ = 4.5V to 28V

5

mV

FB Input Bias Current

-0.1

+0.1

µA

Output Adjustment Range

1

5.5

V

FB = GND

90

190

350

OUT Input Resistance

FB = VCC or adjustable feedback mode

70

145

270

kΩ

Soft-Start Ramp Time

Rising edge of SHDN to full current limit

1.7

ms

TON = GND (600kHz)

140

160

180

TON = REF (450kHz)

175

200

225

TON = unconnected (300kHz)

260

290

320

On-Time

V+ = 24V,
V

OUT

= 2V

(Note 2)

TON = VCC (200kHz)

380

425

470

ns

Minimum Off-Time

(Note 2)

400

500

ns

Quiescent Supply Current (VCC) FB forced above the regulation point

550

800

µA

Quiescent Supply Current (VDD) FB forced above the regulation point

<1

5

µA

Quiescent Supply Current (V+)

25

40

µA

Shutdown Supply Current (VCC) SHDN = GND

<1

5

µA

Shutdown Supply Current (VDD) SHDN = GND

<1

5

µA

Shutdown Supply Current (V+)

SHDN = GND, V+ = 28V, VCC = VDD = 0 or 5V

<1

5

µA

Reference Voltage

VCC = 4.5V to 5.5V, no external REF load

1.98

2.02

V

Reference Load Regulation

I

REF

= 0 to 50µA

0.01

V

FB = OUT
FB = GND 2.475

1.782

2.525

1.818

2.00

MAX1844

High-Speed Step-Down Controller with

Accurate Current Limit for Notebook Computers

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, V+ = 15V, VCC= VDD= 5V, SKIP = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at
T

A

= +25°C.)

PARAMETER

CONDITIONS

MIN

UNITS

REF Sink Current

REF in regulation

10

µA

REF Fault Lockout Voltage

Falling edge, hysteresis = 40mV

1.6

V

Overvoltage Trip Threshold
(Fixed-Threshold Mode)

With respect to error comparator threshold, no load
OVP = GND, rising edge, hysteresis = 1%

12

17

%

External feedback, measured at FB with respect to
V

OVP

, 1V < V

OVP

< 1.8V, rising edge, hysteresis =1%

-30

+30

mV

Overvoltage Comparator Offset
(Adjustable-Threshold Mode)

Internal feedback, measured at OUT with respect to the
nominal OUT regulation voltage, 1V < V

OVP

< 1.8V,

rising edge, hysteresis = 1%

-3.5

+3.5

%

OVP Input Leakage Current

1V < V

OVP

< 1.8V

-100

0

nA

Overvoltage Fault
Propagation Delay

FB forced 2% above trip threshold

1.5

µs

Output Undervoltage Protection
Trip Threshold (Fixed-Threshold
Mode)

65

70

75

%

External feedback, measured at FB with respect to
V

UVP

, 0.4V < V

UVP

< 1V

-40

+40

mV

Output Undervoltage Protection
Trip Threshold (Adjustable­Threshold Mode)

Internal feedback, measured at OUT with respect to the
nominal OUT regulation voltage, 0.4V < V

UVP

< 1V

-5

+5

%

UVP Input Leakage Current

0.4V < V

UVP

< 1V

-100

<1

nA

Output Undervoltage Protection
Blanking Time

From rising edge of SHDN

10

30

ms

PGOOD Trip Threshold (Lower)

With respect to error comparator threshold, no load

-12.5

-10

-8

%

PGOOD Trip Threshold (Upper)

With respect to error comparator threshold, no load

8

10

12.5

%

PGOOD Propagation Delay

FB forced 2% beyond PGOOD trip threshold, falling

10

µs

PGOOD Output Low Voltage

I

SINK

= 1mA

0.4

V

PGOOD Leakage Current

High state, forced to 5.5V

1

µA

ILIM Adjustment Range

0.25

3

V

Current-Limit Threshold (Fixed) GND - VCS, ILIM = V

CC

90

100

110

mV

V

ILIM

= 0.5V

40

50

60

Current-Limit Threshold
(Adjustable)

GND - V

CS

V

ILIM

= 2V

170

200

230

mV

Current-Limit Threshold
(Negative Direction)

GND - VCS, SKIP = VCC, ILIM = VCC ,TA = +25°C

-140

-95

mV

Current-Limit Threshold
(Zero Crossing)

GND - V

CS,

SKIP = GND

3

mV

Thermal Shutdown Threshold

Hysteresis = 10°C

150

°C

VCC Undervoltage
Lockout Threshold

Rising edge, hysteresis = 20mV,
PWM disabled below this level

4.1

4.4

V

With respect to error comparator threshold, UVP = V

CC

TYP

14.5

MAX

+100

+100

-117

MAX1844

High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, V+ = 15V, VCC= VDD= 5V, SKIP = GND, TA= 0°C to +85°C, unless otherwise noted. Typical values are at
T

A

= +25°C.)

PARAMETER

CONDITIONS

MIN

TYP MAX

UNITS

MAX1844EEP

1.5

5

DH Gate-Driver On-Resistance
(Note 4)

BST - LX forced to 5V

MAX1844EGP

1.5

6

Ω

DL, high state

1.5

5

DL Gate-Driver On-Resistance
(Note 4)

DL, low state

0.5

1.7

Ω

DH Gate-Driver
Source/Sink Current

DH forced to 2.5V, BST-LX forced to 5V

1

A

DL Gate-Driver Source Current DL forced to 2.5V

1

A

DL Gate-Driver Sink Current

DL forced to 5V

3

A

DL rising

35

Dead Time

DH rising

26

ns

Logic Input High Voltage

LATCH, SHDN, SKIP

2.4

V

Logic Input Low Voltage

LATCH, SHDN, SKIP

0.8

V

Logic Input Current

LATCH, SHDN, SKIP

-1

+1

µA

Dual Mode Threshold, Low

OVP, UVP, FB

0.15

0.25

V

OVP, UVP

Dual Mode Threshold, High

FB

1.9

2.0

2.1

V

TON VCC Level

V

TON Float Voltage

3.15

3.85

V

TON Reference Level

1.65

2.35

V

TON GND Level

0.5

V

TON Input Current

Forced to GND or V

CC

-3

+3

µA

ILIM Input Leakage Current

-100

0

nA

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, V+ = 15V, VCC= VDD= 5V, SKIP = GND, TA= -40°C to +85°C, unless otherwise noted.) (Note 3)

0.20

VCC - 1.5

VCC - 0.4

PARAMETER CONDITIONS MIN TYP MAX UNITS

Input Voltage Range

Error Comparator Threshold
(DC Output Voltage Accuracy)
(Note 1)

On-Time

Battery voltage, V+ 2 28
V

V+ = 4.5V to 28V,
SKIP = V

V+ = 24V,
V
(Note 2)

, V

CC

DD

= 2V

OUT

CC

VCC - 0.4

+100

FB = OUT 0.985 1.015
FB = GND 2.462 2.538

FB = V

CC

TON = GND (600kHz) 140 180
TON = REF(450kHz) 175 225
TON = Unconnected (300kHz) 260 320
TON = V

(200kHz) 380 470

CC

4.5 5.5

1.773 1.827

V

V

ns

MAX1844

High-Speed Step-Down Controller with

Accurate Current Limit for Notebook Computers

_______________________________________________________________________________________ 5

PARAMETER CONDITIONS

UNITS

Minimum Off-Time (Note 2) 500 ns

Quiescent Supply Current (V

CC

)

FB forced above the regulation point 800 µA

Quiescent Supply Current (V

DD

)

FB forced above the regulation point 5 µA
Quiescent Supply Current (V+) Measured at V+ 40 µA
Shutdown Supply Current (V

CC

) SHDN = GND 5 µA

Shutdown Supply Current (V

DD

) SHDN = GND 5 µA

Shutdown Supply Current (V+) SHDN = GND, V+ = 28V, V

CC

= VDD = 0 or 5V 5 µA

Reference Voltage V

CC

= 4.5V to 5.5V, no external REF load

V

Overvoltage Trip Threshold
(Fixed-Threshold Mode)

With respect to error comparator threshold, no load

OVP = GND, rising edge, hysteresis = 1%

12 17 %

External feedback, measured at FB with respect to

V

OVP

, 1V < V

OVP

1.8V, rising edge, hysteresis = 1%

-30

mV

Overvoltage Comparator Offset
(Adjustable-Threshold Mode)

Internal feedback, measured at OUT with respect to the

nominal OUT regulation voltage, 1V < V

OVP

< 1.8V

%

PGOOD Trip Threshold (Lower)

With respect to error comparator threshold, no load

OUT falling edge, hysteresis = 1%

%

PGOOD Trip Threshold (Upper)

With respect to error comparator threshold, no load

OUT rising edge, hysteresis = 1%

7.5

%

PGOOD Output Low Voltage I

SINK

= 1mA 0.4 V

PGOOD Leakage Current High state, forced to 5.5V 1 µA
Current-Limit Threshold (Fixed) GND - V

CS

, ILIM = V

CC

85 115 mV

GND - V

CS

, V

ILIM

= 0.5V 35 65

Current-Limit Threshold

(Adjustable)

GND - V

CS

, V

ILIM

= 2V 160 240

mV

V

CC

Undervoltage

Lockout Threshold

Rising edge, hysteresis = 20mV,

PWM disabled below this level

4.1 4.4 V

Logic Input High Voltage LATCH, SHDN, SKIP 2.4 V
Logic Input Low Voltage LATCH, SHDN, SKIP 0.8 V
Logic Input Current LATCH, SHDN, SKIP -1 1 µA

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, V+ = 15V, VCC= VDD= 5V, SKIP = GND, TA= -40°C to +85°C, unless otherwise noted.) (Note 3)

Note 1: When the inductor is in continuous conduction, the output voltage will have a DC regulation level higher than the error com-

parator threshold by 50% of the ripple. In discontinuous conduction (SKIP = GND, light load), the output voltage will have a
DC regulation level higher than the trip level by approximately 1.5% due to slope compensation.

Note 2: On-time and off-time specifications are measured from 50% point to 50% point at the DH pin with LX = GND, V

BST

= 5V,

and a 250pF capacitor connected from DH to LX. Actual in-circuit times may differ due to MOSFET switching speeds.

Note 3: Specifications to -40°C are guaranteed by design, not production tested.
Note 4: Production testing limitations due to package handling require relaxed maximum on-resistance specifications for the QFN

package. The MAX1844EEP and MAX1844EGP contain the same die and the QFN package imposes no additional resis­tance in-circuit.

MIN TYP MAX

1.98

-3.5

-12.5

2.02

+30

+3.5

-7.5

12.5

MAX1844

High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers

6 _______________________________________________________________________________________

100

60

0.01 1 10

EFFICIENCY vs. LOAD CURRENT

70
65

75

80

85

90

95

MAX1844 toc01

LOAD CURRENT (A)

EFFICIENCY (%)

0.1

VIN = 7V

VIN = 12V

VIN = 20V

350

0

0.01 1 10

FREQUENCY vs. LOAD CURRENT

100

50

150

200

250

300

MAX1844 toc02

LOAD CURRENT (A)

FREQUENCY (kHz)

0.1

VIN = 15V, SKIP = V

CC

VIN = 15V, SKIP = GND

VIN = 7V, SKIP = GND

VIN = 7V, SKIP = V

CC

320

310

300

290

280

0155 10 202530

FREQUENCY vs. INPUT VOLTAGE

MAX1844 toc03

INPUT VOLTAGE (V)

FREQUENCY (kHz)

I

LOAD

= 1A

290

300

310

320

330

-40 -10 20 50-25 5 35 65 80

FREQUENCY vs. TEMPERATURE

MAX1844 toc04

TEMPERATURE (°C)

FREQUENCY (kHz)

I

LOAD

= 1A

I

LOAD

= 4A

-40 5 20-25 -10 35 50 65 80

CURRENT LIMIT vs. TEMPERATURE

MAX1844 toc07

TEMPERATURE (°C)

CURRENT LIMIT (A)

3

4

5

6

0

100

200

300

400

500

600

700

800

0105 15202530

CONTINUOUS-TO-DISCONTINUOUS INDUCTOR

CURRENT vs. INPUT VOLTAGE

MAX1844 toc05

INPUT VOLTAGE (V)

LOAD CURRENT (mA)

CONTINUOUS INDUCTOR CURRENT

DISCONTINUOUS INDUCTOR CURRENT

0

1

2

3

4

5

6

7

8

0105 15202530

CURRENT LIMIT vs. INPUT VOLTAGE

MAX1844 toc06

INPUT VOLTAGE (V)

CURRENT LIMIT (A)

1.8

1.6

1.4

1.2

1.0

1.0 1.41.2 1.6 1.8

NORMALIZED OVERVOLTAGE

TRIP THRESHOLD vs. V

OVP

MAX1844 toc08

V

OVP

(V)

NORMALIZED THRESHOLD (V/V)

OVERVOLTAGE TRIP THRESHOLD

OUTPUT VOLTAGE SET POINT

110

112

116

114

118

120

-40 10-15 35 60 85

OVERVOLTAGE TRIP THRESHOLD

vs. TEMPERATURE

MAX1844 toc09

TEMPERATURE (°C)

OVERVOLTAGE TRIP THRESHOLD (%)

__________________________________________Typical Operating Characteristics

(Circuit of Figure 1, VIN= 15V, SKIP = GND, TON = unconnected, TA= +25°C, unless otherwise noted.)

MAX1844

High-Speed Step-Down Controller with

Accurate Current Limit for Notebook Computers

_______________________________________________________________________________________ 7

0

2

6

4

8

10

0105 15202530

NO-LOAD SUPPLY CURRENT

vs. INPUT VOLTAGE (PWM MODE)

MAX1844 toc10

INPUT VOLTAGE (V)

SUPPLY CURRENT (mA)

I

IN

I

DD

I

CC

0.8

0.6

0.4

0.2

0

015510 202530

NO-LOAD SUPPLY CURRENT

vs. INPUT VOLTAGE (SKIP MODE)

MAX1844 toc11

INPUT VOLTAGE (V)

SUPPLY CURRENT (mA)

I

CC

I

IN

I

DD

20µs/div

LOAD-TRANSIENT RESPONSE

(PWM MODE)

INDUCTOR
CURRENT
2A/div

V

OUT

AC COUPLED
100mV/div

DL
5V/div

MAX1844 toc12A

20µs/div

LOAD-TRANSIENT RESPONSE

(SKIP MODE)

INDUCTOR
CURRENT
2A/div

V

OUT

AC COUPLED
100mV/div

DL
5V/div

MAX1844 toc12B

500µs/div

STARTUP WAVEFORM

INDUCTOR
CURRENT
5A/div

V

OUT

1V/div

MAX1844 toc14

SHDN
5V/div

DL
5V/div

40µs/div

OUTPUT OVERLOAD WAVEFORM

(UVP = GND)

V

OUT

1V/div

DL
5V/div

INDUCTOR
CURRENT
5A/div

MAX1844 toc13A

R

LOAD

= 112m

Ω

40µs/div

OUTPUT OVERLOAD WAVEFORM

(UVP = V

CC

, OVP = GND)

V

OUT

1V/div

DL
5V/div

INDUCTOR
CURRENT
5A/div

MAX1844 toc13B

R

LOAD

= 112m

Ω

100µs/div

SHUTDOWN WAVEFORM

(OVP = GND)

V

OUT

1V/div

DL
5V/div

INDUCTOR
CURRENT
5A/div

MAX1844 toc15A

R

LOAD

= 1Ω

100µs/div

SHUTDOWN WAVEFORM

(OVP = V

CC

)

V

OUT

1V/div

DL
5V/div

INDUCTOR
CURRENT
5A/div

MAX1844 toc15B

R

LOAD

= 1Ω

Typical Operating Characteristics (continued)

(Circuit of Figure 1, VIN= 15V, SKIP = GND, TON = unconnected, TA= +25°C, unless otherwise noted.)