Rainbow Electronics MAX1845 User Manual

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.

General Description

The MAX1845 is a dual PWM controller configured for step-down (buck) topologies that provides high efficiency, excellent transient response, and high DC output accuracy necessary for stepping down high-voltage batteries to generate low-voltage chipset and RAM power supplies in notebook computers. The CS_ inputs can be used with low-side sense resistors to provide accurate current limits or can be connected to LX_, using low-side MOSFETs as current-sense elements.

The on-demand PWM controllers are free running, constant on-time with input feed-forward. This configuration provides ultra-fast transient response, wide input-output differential range, low supply current, and tight load-regulation characteristics. The MAX1845 is simple and easy to compensate.

Single-stage buck conversion allows the MAX1845 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 MAX1845 is intended for generating chipset, DRAM, CPU I/O, or other low-voltage supplies down to 1V. For a single-output version, refer to the MAX1844 data sheet. The MAX1845 is available in a 28-pin QSOP package.

Applications

Notebook Computers

CPU Core Supplies

Chipset/RAM Supply as Low as 1V

1.8V and 2.5V I/O Supplies

Features

♦ Ultra-High Efficiency

♦ Accurate Current-Limit Option

♦ Quick-PWM™ with 100ns Load-Step Response

♦ 1% V

OUT

Accuracy over Line and Load

♦ Dual Mode™ Fixed 1.8V/1.5V/Adj or 2.5V/Adj Outputs

♦ Adjustable 1V to 5.5V Output Range

♦ 2V to 28V Battery Input Range

♦ 200/300/420/540kHz Nominal Switching Frequency

♦ Adjustable Overvoltage Protection

♦ 1.7ms Digital Soft-Start

♦ Drives Large Synchronous-Rectifier FETs

♦ Power-Good Window Comparator

♦ 2V ±1% Reference Output

MAX1845

Dual, High-Efficiency, Step-Down

Controller with Accurate Current Limit

________________________________________________________________ Maxim Integrated Products 1

19-1955; Rev 1; 3/02

Pin Configuration appears at end of data sheet.

Quick-PWM and Dual Mode are trademarks of Maxim Integrated Products.

-40°C to +85°C

PART

MAX1845EEI

TEMP RANGE PIN-PACKAGE

28 QSOP

Ordering Information

EVALUATION KIT

AVAILABLE

OUTPUT1

1.8V

BATTERY

4.5V TO 28V

ILIM1

ON2

DL1

TON

OUT1

LX1

DH1

FB1

GND

BST1

ILIM2 ON1

REF

DL2

CS2

OUT2

LX2

DH2

FB2

V+

BST2

SKIP

5V INPUT

PGOOD

OUTPUT2

2.5V

MAX1845

UVP

OVP

CS1

Minimal Operating Circuit

MAX1845

Dual, High-Efficiency, Step-Down Controller with Accurate Current Limit

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 ................................................................-0.3 to +30V

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

PGOOD, OUT_ to GND ............................................-0.3V to +6V

OVP, UVP, ILIM_, FB_, REF,

SKIP, TON, ON_ to GND ........................-0.3V to (VCC+ 0.3V)

DL_ to GND ................................................-0.3V to (V

+ 0.3V)

BST_ to GND ..........................................................-0.3V to +36V

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

DH1 to LX1 ..............................................-0.3V to (V

BST1

+ 0.3V)

LX_ to BST_ ..............................................................-6V to +0.3V

DH2 to LX2 ..............................................-0.3V to (V

BST2

+ 0.3V)

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

Continuous Power Dissipation (T

= +70°C)

28-Pin QSOP (derate 10.8mW/°C above +70°C)........860mW

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, VDD= V

= 5V, SKIP = GND, V+ = 15V, TA= 0°C to +85°C, typical values are at +25°C, unless otherwise

noted.) (Note 1)

PARAMETER

CONDITIONS

UNITS

PWM CONTROLLERS

V+ Battery voltage, V+ 2 28

Input Voltage Range

VCC, V

4.5 5.5

FB1 to GND

1.8

FB1 to V

1.5

V+ = 2V to 28V, I

LOAD

= 0 to 8A, SKIP = VCC, +25°C to +85°C

FB1 to OUT1

FB1 to GND

1.8

FB1 to V

1.5

DC Output Voltage OUT1 (Note 2)

V+ = 2V to 28V, I

LOAD

= 0 to 8A, SKIP = VCC, 0°C to +85°C

FB1 to OUT1

FB2 to GND

2.5

V+ = 4.5V to 28V, I

LOAD

= 0 to 4A,

SKIP = V

+25°C to +85°C

FB2 to OUT2

FB2 to GND

2.5

DC Output Voltage OUT2

(Note 2)

V+ = 4.5V to 28V, I

LOAD

= 0 to 4A,

SKIP = V

0°C to +85°C

FB2 to OUT2

Output Voltage Adjust Range OUT1, OUT2 1 5.5 V

Dual-Mode Threshold, Low OVP, FB_

0.1

OVP, ILIM_

1.5

0.4

Dual-Mode Threshold, High

FB1 1.9 2.0 2.1

OUT1

= 1.5V 75

OUT_ Input Resistance

OUT2

= 2.5V 100

kΩ

FB_ Input Bias Current I

0.1 µA

Soft-Start Ramp Time Zero to full ILIM

µs

TON = GND 120 137

TON = REF 153 174

TON = float 222 247

On-Time, Side 1 (Note 3) t

ON1

V+ = 24V, V

OUT1

= 2V

TON = V

316 353

SYMBOL

VCC/V

OUT1

OUT2

OUT1

OUT2

MIN TYP MAX

1.782

1.485

0.99

1.773

1.477

0.985

2.475

0.99

2.463

0.985

0.05

-0.1

1700

1.818

1.515

1.01

1.827

1.523

1.015

2.525

1.01

2.537

1.015

0.15

153

195

272

390

MAX1845

Dual, High-Efficiency, Step-Down

Controller with Accurate Current Limit

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VDD= V

= 5V, SKIP = GND, V+ = 15V, TA= 0°C to +85°C, typical values are at +25°C, unless otherwise

noted.) (Note 1)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

TON = GND 160 182

TON = REF 205 234

TON = float 301 336

On-Time, Side 2 (Note 3) t

ON2

V+ = 24V, V

OUT2

= 2V

TON = V

432 483

TON = GND 125 135

TON = REF 125 135

TON = float 125 135

On-Time Tracking (Note 3)

On-time 2 with respect to ontime 1

TON = V

125 135

Minimum Off-Time (Note 3) t

OFF

400

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

µA

Quiescent Supply Current (VDD)IDDFB_ forced above the regulation point <1 5 µA

Quiescent Supply Current (V+) I+ Measured at V+ 25 70 µA

ON1 = ON2 = GND, OVP = VCC or GND <1 5

Shutdown Supply Current (VCC)

ON1 = ON2 = GND, V

OVP

= 1.8V 1 5

µA

Shutdown Supply Current (VDD) ON1 = ON2 = GND <1 5 µA

Shutdown Supply Current (V+)

ON1 = ON2 = GND, measured at V+, V

= GND or 5V

<1 5 µA

Reference Voltage V

REF

= 4.5V to 5.5V, no external REF load

Reference Load Regulation I

REF

= 0 to 50µA

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)

OVP = GND, with respect to errorcomparator trip threshold

112 114

1V < V

OVP

< 1.8V, external feedback,

measured at FB_ with respect to V

OVP

-28 0 28 mV

Overvoltage Comparator Offset (Adjustable-Threshold Mode)

1V < V

OVP

< 1.8V, internal feedback, measured at OUT_ with respect to OUT_ regulation point

OVP Input Leakage Current 1V < V

OVP

< 1.8V

Overvoltage Fault Propagation Delay

FB_ forced 2% above trip threshold 1.5 µs

Output Undervoltage Threshold

UVP = VCC, with respect to error-comparator trip threshold

65 70 75 %

Output Undervoltage Protection Blanking Time

From ON_ signal going high 10 30 ms

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

40 50 60 mV

1100 1500

1.98

-3.5

-100

204

263

371

534

145

500

2.02

0.01

117

+3.5

100

MAX1845

Dual, High-Efficiency, Step-Down Controller with Accurate Current Limit

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VDD= V

= 5V, SKIP = GND, V+ = 15V, TA= 0°C to +85°C, typical values are at +25°C, unless otherwise

noted.) (Note 1)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

GND - VCS, V

ILIM

_ = 0.5V 40 50 60

Current-Limit Threshold (Adjustable)

GND - V

, V

ILIM

_ = 1V 85 100

ILIM_ Adjustment Range

0.3 2.5 V

Negative Current-Limit Threshold (Fixed)

CS_ = GND, ILIM_ = V

, TA = +25 oC -75 -60

Thermal Shutdown Threshold Hysteresis = 15oC 160

VCC Undervoltage Lockout Threshold

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

4.4 V

DH_ Gate Driver On-Resistance V

BST

_ = VLX_ = 5V 1.5 5 Ω

DL_ Gate Driver On-Resistance (Pullup)

DL_, high state 1.5 5 Ω

DL_ Gate Driver On-Resistance (Pulldown)

DL_, low state 0.5 1.7 Ω

DH_ Gate Driver Source/Sink Current

_ = 2.5V, V

BST

_ = VLX_ = 5V 1 A

DL_ Gate Driver Sink Current VDL_ = 2.5V 3 A

DL_ Gate Driver Source Current VDL_ = 2.5V 1 A

ON_, SKIP 2.4

Logic Input High Voltage V

UVP

0.4

ON_, SKIP 0.8

Logic Input Low Voltage V

UVP

TON Threshold TON

0.4

Float level

REF level

TON

GND level 0.5

Logic Input Current TON (GND or VCC)-33µA Logic Input Current ON_, SKIP, UVP -1 1 µA

PGOOD Trip Threshold (Lower)

With respect to error-comparator trip threshold, falling edge

-10

PGOOD Trip Threshold (Upper)

With respect to error-comparator trip threshold, rising edge

PGOOD Propagation Delay

Falling edge, FB_ forced 2% below PGOOD trip threshold

1.5 µs

PGOOD Output Low Voltage I

SINK

= 1mA 0.4 V

PGOOD Leakage Current High state, forced to 5.5V 1 µA

ILIM

115

4.05

3.15 3.85

1.65 2.35

-12.5

+7.5 +10 +12.5

-45

0.05

-7.5

MAX1845

Dual, High-Efficiency, Step-Down

Controller with Accurate Current Limit

_______________________________________________________________________________________ 5

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, VDD= V

= 5V, SKIP = GND, V+ = 15V, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

PWM CONTROLLERS

V+ Battery voltage, V+ 2 28

Input Voltage Range

VCC, V

4.5 5.5

FB1 to GND

FB1 to V

D C O utp ut V ol tag e, O U T1 ( N ote 2)

V+ = 2V to 28V, SKIP = VCC, I

LOAD

= 0 to 10A

FB2 to GND

D C O utp ut V ol tag e, O U T2 ( N ote 2)

V+ = 2V to 28V, SKIP = VCC, I

LOAD

= 0 to 10A

Output Voltage Adjust Range OUT1, OUT2 1 5.5 V

Dual-Mode Threshold (Low) OVP, FB_

OVP, ILIM_

1.5

0.4

Dual-Mode Threshold (High)

FB_ 1.9 2.1

OUT1

= 1.5V 75

OUT_ Input Resistance

OUT2

= 2.5V

kΩ

FB_ Input Bias Current I

0.1 µA

TON = GND

153

TON = REF

195

TON = float

272

On-Time, Side 1 (Note 3) t

ON1

TON = V

390

TON = GND

204

TON = REF

263

TON = float

371

On-Time, Side 2 (Note 3) t

ON2

TON = V

534

TON = GND

145

TON = REF

145

TON = float

145

On-Time Tracking (Note 3)

On-time 2, with respect to on-time 1

TON = V

145

Minimum Off-Time (Note 3) t

OFF

500 ns

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

µA

Quiescent Supply Current (VDD)IDDFB forced above the regulation point 5 µA

Quiescent Supply Current (V+) I+ Measured at V+ 70 µA

Reference Voltage V

REF

= 4.5V to 5.5V, no external REF load

Reference Load Regulation I

REF

= 0 to 50uA

Overvoltage Trip Threshold (Fixed-Threshold Mode)

OVP = GND, with respect to FB_ regulation point, no load

117 %

Output Undervoltage Threshold

UVP = V

, with respect to FB_ regulation

point, no load

65 75 %

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

35 65 mV

VCC/V

1.773 1.827

OUT1

1.477 1.523

FB1 to OUT1 0.985 1.015

OUT2

FB2 to OUT2 0.985 1.015

2.463 2.537

OUT1

OUT2

0.05 0.15

100

-0.1

120

V+ = 24V, V

OUT1

= 2V

V+ = 24V, V

OUT2

= 2V

153

217

308

160

205

295

422

125

1.98 2.02

112

1500

0.01

MAX1845

Dual, High-Efficiency, Step-Down Controller with Accurate Current Limit

6 _______________________________________________________________________________________

0.01 1010.1

300

350

400

200

250

100

150

MAX1845 toc01

LOAD CURRENT (A)

FREQUENCY (kHz)

FREQUENCY vs. LOAD CURRENT

OUT1, SKIP = V

OUT2, SKIP = V

OUT1, SKIP = GND

OUT2, SKIP = GND

100

150

200

250

300

350

400

4 8 12 16 20 21

MAX1845 toc02

INPUT VOLTAGE (V)

FREQUENCY (kHz)

FREQUENCY vs. INPUT VOLTAGE

(TON = FLOAT, SKIP = V

)

OUT1

OUT2

OUT1

= 8A

OUT2

= 4A

__________________________________________Typical Operating Characteristics

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

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VDD= V

= 5V, SKIP = GND, V+ = 15V, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)

Note 1: Specifications to -40°C are guaranteed by design, not production tested. Note 2: When the inductor is in continuous conduction, the output voltage will have a DC regulation level higher than the error compara-

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

Note 3: On-time and off-time specifications are measured from 50% point to 50% point at DH_ with LX_ = GND, BST_ = 5V, and a

250pF capacitor connected from DH_ to LX_. Actual in-circuit times may differ due to MOSFET switching speeds.

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

GND - VCS, V

ILIM

_ = 0.5V 35 65

Current-Limit Threshold (Adjustable)

GND - V

, V

ILIM

_ = 1V 80 120

VCC Undervoltage Lockout Threshold

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

4.4 V

ON_, SKIP 2.4

Logic Input High Voltage V

UVP

0.4

ON_, SKIP 0.8

Logic Input Low Voltage V

UVP

TON (GND or VCC)-33

Logic Input Current

ON_, SKIP, UVP -1 1

µA

4.05

0.05

MAX1845

Dual, High-Efficiency, Step-Down

Controller with Accurate Current Limit

_______________________________________________________________________________________ 7

4.5

3.0

1.5

6.0

7.5

9.0

10.5

12.0

13.5

15.0

51510 20 25 30

MAX1845 toc03A

SUPPLY VOLTAGE V+ (V)

SUPPLY CURRENT (mA)

NO-LOAD SUPPLY CURRENT

vs. INPUT VOLTAGE (SKIP = V

)

VCC = VDD = 5V

I+ (25µA TYP)

100

200

300

400

500

600

700

800

900

1000

1100

MAX1845 toc03B

SUPPLY VOLTAGE V+ (V)

SUPPLY CURRENT (µA)

5 1015202530

NO-LOAD SUPPLY CURRENT

vs. INPUT VOLTAGE (SKIP = GND)

VCC = VDD = 5V

IDD (600nA typ)

I+

0.01 1010.1

100

MAX1845 toc04a

LOAD CURRENT (A)

EFFICIENCY (%)

EFFICIENCY vs. LOAD CURRENT

(8A COMPONENTS, SKIP = V

)

V+ = 7V

V+ = 20V

V+ = 12V

OUT1 = 1.8V

0.01 1010.1

100

MAX1845 toc04b

LOAD CURRENT (A)

EFFICIENCY (%)

EFFICIENCY vs. LOAD CURRENT (8A COMPONENTS, SKIP = GND)

V+ = 7V

V+ = 20V

OUT1 = 1.8V

V+ = 12V

50 30

110

130

150

170

190

210

230

250

0 0.5 1.0 1.5 2.0 2.5

CURRENT-LIMIT TRIP POINT

vs. ILIM VOLTAGE

MAX1845 toc05

ILIM VOLTAGE (V)

CURRENT-LIMIT TRIP POINT (mV)

0.01 1010.1

100

MAX1845 toc04c

LOAD CURRENT (A)

EFFICIENCY (%)

EFFICIENCY vs. LOAD CURRENT

(4A COMPONENTS, SKIP = V

)

V+ = 7V

V+ = 20V

V+ = 12V

OUT2 = 2.5V

0.01 1010.1

100

MAX1845 toc04d

LOAD CURRENT (A)

EFFICIENCY (%)

EFFICIENCY vs. LOAD CURRENT (4A COMPONENTS, SKIP = GND)

V+ = 7V

V+ = 12V

V+ = 20V

OUT2 = 2.5V

1.0

1.2

1.1

1.4

1.3

1.6

1.5

1.7

1.9

1.8

2.0

1.0 1.2 1.31.1 1.4 1.5 1.6 1.7 1.8

MAX1845 toc06

OVP VOLTAGE (V)

NORMALIZED THRESHOLD (V)

NORMALIZED OVERVOLTAGE PROTECTION

THRESHOLD vs. OVP VOLTAGE

MAX1845 toc07a

OUT2

2A/div

20µs/div

OUT2

100mV/div

LOAD-TRANSIENT RESPONSE

(4A COMPONENTS, PWM MODE, V

OUT2

= 2.5V)

Typical Operating Characteristics (continued)

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

MAX1845

Dual, High-Efficiency, Step-Down Controller with Accurate Current Limit

8 _______________________________________________________________________________________

MAX1845 toc09

400µs/div

OUT2

1V/div

OUT2

2A/div

STARTUP WAVEFORM

(4A COMPONENTS, SKIP = GND, V

OUT2

= 2.5V)

MAX1845 toc09

100µs/div

OUT2

1V/div

OUT2

5A/div

SHUTDOWN WAVEFORM

(4A COMPONENTS, SKIP = GND, V

OUT2

= 2.5V)

Typical Operating Characteristics (continued)

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

PIN NAME FUNCTION

1 OUT1

Output Voltage Connection for the OUT1 PWM. Connect directly to the junction of the external inductor and output filter capacitors. OUT1 senses the output voltage to determine the on-time and also serves as the feedback input in fixed-output modes.

2 FB1

Feedback Input for OUT1. Connect to GND for 1.8V fixed output or to V

for 1.5V fixed output, or

connect to a resistor-divider network from OUT1 for an adjustable output between 1V and 5.5V.

3 ILIM1

Current-Limit Threshold Adjustment for OUT1. The current-limit threshold at CS1 is 0.1 times the voltage at ILIM1. Connect a resistor-divider network from REF to set the current-limit threshold between 25mV and 250mV (with 0.25V to 2.5V at ILIM). Connect to V

to assert 50mV default

current-limit threshold.

4V+

Battery Voltage-Sense Connection. Connect to input power source. V+ is only used to adjust the DH_ on-time for pseudo-fixed-frequency operation.

On-Time Selection Control Input. This four-level input pin sets the DH_ on-time to determine the operating frequency.

TON FREQUENCY (OUT1) (kHz) FREQUENCY (OUT2) (kHz)

GND 620 460

REF 485 355

Open 345 255

5 TON

235 170

Pin Description

MAX1845 toc07b

OUT1

5A/div

20µs/div

OUT1

100mV/div

LOAD-TRANSIENT RESPONSE

(8A COMPONENTS, PWM MODE, V

OUT1

= 1.8V)

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