Rainbow Electronics MAX8720 User Manual

General Description

The MAX8720 step-down controller is intended for core
CPU DC-DC converters in notebook computers. It fea­tures a dynamically adjustable output, ultra-fast transient
response, high DC accuracy, and the high efficiency
needed for leading-edge CPU core power supplies.
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.

The output voltage can be dynamically adjusted through
the 6-bit digital-to-analog converter (DAC) over a 0.275V
to 1.850V range in 25mV steps. The MAX8720 has inde­pendent four-level logic inputs for setting the suspend
voltage (S0-S1). Precision slew-rate control provides
“just-in-time” arrival at the new DAC setting, minimizing
surge currents to and from the battery. The internal DAC
of the MAX8720 is synchronized to the slew-rate clock
for improved operation under aggressive power man­agement of newer chipsets and operating systems that
can make incomplete mode transitions. Remote feed­back and ground-sense inputs allow easy compensa­tion for IR drops in PC board traces.

Single-stage buck conversion allows these devices 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 MAX8720 is available in a 28-pin QSOP or 36-pin
6mm x 6mm thin QFN package.

Applications

CPU Core Supply Converters

GPU Core Supply Converters

Notebook and Subnotebook Computers

Features

♦ Quick-PWM Architecture
♦ ±1% V

OUT

Accuracy Over Line and Load

♦ 6-Bit On-Board DAC with Input Muxes
♦ Precision-Adjustable V

OUT

Slew Control

♦ 0.275V to 1.850V Output Adjust Range
♦ Remote Feedback and Ground Sense
♦ Supports Voltage-Positioned Applications
♦ 2V to 28V Battery Input Range
♦ 200kHz/300kHz/550kHz/1000kHz Switching

Frequency

♦ Over/Undervoltage Protection
♦ Drives Large Synchronous-Rectifier FETs
♦ 800µA (typ) ICCSupply Current
♦ 10µA (typ) Shutdown Supply Current
♦ 2V ±0.75% Reference Output
♦ PGOOD Blanking During Transition

MAX8720

Dynamically Adjustable 6-Bit VID

Step-Down Controller

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

MAX8720

PGOOD

VID0

VID1

VID2

VID3

VID4

VID5

SUS

AGND

OUTPUT (V

OUT

)

0.275V TO 1.850V

INPUT (V

IN

)

7V TO 28V

BST

V+

DH

LX

DL

PGND

FB

V

CC

V

DD

SHDN

+5V BIAS

FBS

GNDS

CC

REF

TIME

SKIP

D0

D1

D2

D3

D4

D5

S0

S1

ILIM

Minimal Operating Circuit

19-3319; Rev 1; 8/04

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.

EVALUATION KIT

AVAILABLE

PART

PIN-PACKAGE

MAX8720EEI

28 QSOP

MAX8720ETX

36 Thin QFN 6mm x 6mm

Quick-PWM is a trademark of Maxim Integrated Products, Inc.

Pin Configurations appear at end of data sheet.

TEMP RANGE

-40°C to +85°C

-40°C to +85°C

MAX8720

Dynamically Adjustable 6-Bit VID
Step-Down Controller

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS (Note 1)

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.

VCCto AGND............................................................-0.3V to +6V

V

DD

to PGND............................................................-0.3V to +6V

AGND to PGND .....................................................-0.3V to +0.3V

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

SHDN to AGND ......................................................-0.3V to +16V

D0–D5, PGOOD, SUS, SKIP to AGND .....................-0.3V to +6V

FB, FBS, GNDS to AGND...........................-0.3V to (V

CC

+ 0.3V)

CC, ILIM, REF, TIME to AGND ...................-0.3V to (V

CC

+ 0.3V)

S0, S1, TON to AGND ................................-0.3V to (V

CC

+ 0.3V)

BST to PGND..........................................................-0.3V to +36V

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

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

DL to PGND................................................-0.3V to (V

DD

+ 0.3V)

REF Short Circuit to AGND.........................................Continuous

Continuous Power Dissipation (T

A

= +70°C)

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

36-Pin TQFN (derate 26.3mW/°C above +70°C) .....2105mW

Operating Temperature

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

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

Storage Temperature Range .............................-65°C to +165°C

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

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, V+ = 15V, SHDN = SKIP = VDD= VCC= +5V, V

OUT

= 1.25V, TA= 0°C to +85°C, unless otherwise noted. Typical

values are at T

A

= +25°C.)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

PWM CONTROLLER

Battery voltage, V+ 2 28

Input Voltage Range

V

CC

, V

DD

4.5 5.5

V

DAC codes from

0.9V to 1.85V

-1 +1 %

DAC codes from

0.45V to 0.875V

-10

DC Output Voltage Accuracy

V+ = 4.5V to 28V,
includes load
regulation error

DAC codes from

0.275V to 0.425V

-18

mV

Line Regulation Error VCC = 4.5V to 5.5V, V+ = 4.5V to 28V 5 mV

Remote-Sense Voltage Error FB to FBS or AGND to GNDS = 0 to 25mV 3 mV

FBS Input Bias Current FB, FBS

µA

GNDS Input Bias Current GNDS -1 +1 µA

FB Input Resistance

kΩ

150kHz, R

TIME

= 120kΩ -8 +8

818kHz, R

TIME

= 22kΩ -12

TIME Frequency Accuracy

38kHz, R

TIME

= 470kΩ -12

%

V+ = 5V, FB = 1.25V, TON = GND
(1000kHz)

TON = REF
(550kHz)

TON = open
(300kHz)

On-Time (Note 2) t

ON

V+ = 12V,
FB = 1.25V

TON = V

CC

(200kHz)

ns

Note 1: For the MAX8720EEI, AGND and PGND refer to a single pin designated GND.

-0.2 +0.2

115 180 265

230 260 290

165 190 215

320 355 390

465 515 565

+10

+18

+12

+12

MAX8720

Dynamically Adjustable 6-Bit VID

Step-Down Controller

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, V+ = 15V, SHDN = SKIP = VDD= VCC= +5V, V

OUT

= 1.25V, TA= 0°C to +85°C, unless otherwise noted. Typical

values are at T

A

= +25°C.)

PARAMETER

CONDITIONS

UNITS

TON = VCC, open, or REF (200kHz, 300kHz,
or 550kHz)

Minimum Off-Time (Note 2)

)

TON = GND (1000kHz)

ns

BIAS AND REFERENCE

Quiescent Supply Current (VCC)ICCFB forced above their regulation points

µA

Quiescent Supply Current (VDD)IDDFB forced above their regulation points <1 5 µA

Quiescent Battery Supply
Current (V+)

I

+

25 40 µA

Shutdown Supply Current (VCC)ICCSHDN = GND 10 25 µA

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

Shutdown Battery Supply
Current (V+)

I

+

SHDN = GND, VCC = VDD = 0V or 5V <1 5 µA

Reference Voltage V

REF

VCC = 4.5V to 5.5V,
I

REF

= 0

T

A

= 0°C to +85°C

V

Reference Load Regulation ∆V

REFIREF

= 0 to 50µA

V

REF Sink Current REF in regulation 10 µA

FAULT DETECTION

VCC Undervoltage-Lockout
Threshold

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

4.1 4.4 V

Output Overvoltage Trip
Threshold

V

Output Overvoltage Fault­Propagation Delay

t

OVP

FB forced 2% above regulation 10 µs

Output Undervoltage-Protection
Trip Threshold

With respect to unloaded output voltage 65 70 75 %

Output Undervoltage Fault­Propagation Delay

t

UVP

FB forced 2% below trip threshold 10 µs

PGOOD Transition Blanking Time

After X = Y, clock speed set by R

TIME

8 clk

PGOOD Lower Trip Threshold

Measured at FB with respect to unloaded
output voltage, hysteresis = 1%

-17 -15 -13 %

PGOOD Upper Trip Threshold

Measured at FB with respect to unloaded
output voltage, hysteresis = 1%

%

PGOOD Propagation Delay

Falling edge, 50mV overdrive 10 µs

PGOOD Output Low Voltage I

SINK

= 4mA 0.4 V

PGOOD Leakage Current

High state, PGOOD forced to 5.5V 1 µA

Thermal-Shutdown Threshold T

SHDN

Hysteresis = 10°C

°C

CURRENT LIMIT

ILIM Adjustment Range 0.5

V

SYMBOL

t

OFF(MIN

t

PGOOD

I

PGOOD

MIN TYP MAX

400 500

300 375

700 1200

TA = + 25°C to + 85°C 1.985 2.00 2.015

1.98 2.00 2.02

2.20 2.25 2.30

+13 +15 +17

+150

0.01

V

REF

MAX8720

Dynamically Adjustable 6-Bit VID
Step-Down Controller

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, V+ = 15V, SHDN = SKIP = VDD= VCC= +5V, V

OUT

= 1.25V, TA= 0°C to +85°C, unless otherwise noted. Typical

values are at T

A

= +25°C.)

PARAMETER

CONDITIONS

UNITS

90

Current-Limit Threshold (Fixed) V

LIMIT

V

PGND

- V

LX

,

ILIM = V

CC T

A

= 0°C to +85°C85

mV

V

ILIM

= 2.00V

Current-Limit Threshold
(Adjustable)

V

LIMIT

V

PGND

- V

LX

V

ILIM

= 0.50V 35 50 65

mV

VLX - V

PGND

, SKIP = ILIM = VCC,

-90 mV

Current-Limit Threshold
(Negative)

V

NEG

V

LX

- V

PGND

, SKIP = VCC, adjustable mode,

percent of current limit

%

Current-Limit Threshold (Zero
Crossing)

V

ZX

V

PGND

- V

LX

, SKIP = GND 4 mV

Current-Limit Default
Switchover Threshold

3

1

V

CC

-

0.4

V

ILIM Leakage Current 0.1 µA

GATE DRIVERS

QSOP package 1.0 3.5

DH Gate-Driver On-Resistance
(Note 3)

R

DH

TQFN package 1.0 4.5

Ω

QSOP package 1.0 3.5

DL, high state

TQFN package 1.0 4.0

DL Gate-Driver On-Resistance
(Note 3)

R

DL

DL, low state 0.4 1.0

Ω

DH Gate-Driver Source/Sink
Current

I

DH

DH forced to 2.5V, BST-LX forced to 5V 2 A

DL Gate-Driver Source Current

I

DL

(

)

DL forced to 2.5V 1.6 A

DL Gate-Driver Sink Current

)

DL forced to 2.5V 4 A

DL rising 35

Dead Time t

DEAD

DH rising 26

ns

INPUTS AND OUTPUTS

Logic high 2.4

Logic low 0.4

SHDN Input Level V

SHDN

No-fault mode 12 15

V

Logic Input High Voltage V

IH

D0–D5, SKIP, SUS 2.4 V

Logic Input Low Voltage V

IL

D0–D5, SKIP, SUS 0.8 V

Logic Input Current D0–D5, SKIP, SUS -1 +1 µA

High

V

CC

-

0.2

Open

REF

Four-Level Input Logic TON, S0, S1

GND 0.5

V

Input Leakage Current SHDN, TON, S0, S1 forced to VCC or GND -3 +3 µA

SYMBOL

TA = +25°C to +85°C

MIN TYP MAX

100 110

115

165 200 230

-140 -117

-117

BST-LX forced to 5V

VCC -

SOURCE

I

DL (SINK

3.15 3.85

1.65 2.35

MAX8720

Dynamically Adjustable 6-Bit VID

Step-Down Controller

_______________________________________________________________________________________ 5

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, V+ =15V, SHDN = SKIP = V

DD

= VCC= +5V, V

OUT

= 1.25V, TA= -40°C to +85°C, unless otherwise noted.

Typical values are at T

A

= +25°C.) (Note 4)

PARAMETER

CONDITIONS

UNITS

PWM CONTROLLER

Battery Voltage, V+ 2 28

Input Voltage Range

V

CC

, V

DD

4.5 5.5

V

DAC codes from 0.9V
to 1.85V

-1 +1 %

DAC codes from

0.45V to 0.875V

-15

DC Output Voltage Accuracy

V+ = 4.5V to 28V,
includes load
regulation error

DAC codes from

0.275V to 0.425V

-18

mV

FB Input Resistance

265 kΩ

150kHz, R

TIME

= 120kΩ -8 +8

818kHz, R

TIME

= 22kΩ -12

TIME Frequency Accuracy

38kHz, R

TIME

= 470kΩ -12

%

V+ = 5V, FB = 1.25V, TON = GND
(1000kHz)

290

TON = REF
(550kHz)

215

TON = open
(300kHz)

390

On-Time (Note 2) t

ON

V+ = 12V,
FB = 1.25V

TON = V

CC

(200kHz)

565

ns

TON = VCC, open, or REF (200kHz, 300kHz,
or 550kHz)

500

Minimum Off-Time (Note 2)

)

TON = GND (1000kHz) 375

ns

BIAS AND REFERENCE

Quiescent Supply Current (VCC)ICCFB forced above their regulation points

µA

Quiescent Supply Current (VDD)IDDFB forced above their regulation points 5 µA

Quiescent Battery Supply
Current (V+)

I

+

40 µA

Shutdown Supply Current (VCC)ICCSHDN = GND 25 µA

Shutdown Supply Current (VDD)IDDSHDN = GND 5 µA

Shutdown Battery Supply
Current (V+)

I

+

SHDN = GND, VCC = VDD = 0V or 5V 5 µA

Reference Voltage V

REF

VCC = 4.5V to 5.5V, no REF load

V

FAULT DETECTION

VCC Undervoltage-Lockout
Threshold

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

4.1 4.4 V

SYMBOL

t

OFF(MIN

MIN TYP MAX

115

230

165

320

465

1.98 2.02

+15

+18

+12

+12

1300

MAX8720

Dynamically Adjustable 6-Bit VID
Step-Down Controller

6 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, V+ =15V, SHDN = SKIP = V

DD

= VCC= +5V, V

OUT

= 1.25V, TA= -40°C to +85°C, unless otherwise noted.

Typical values are at T

A

= +25°C.) (Note 4)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

Output Overvoltage Trip
Threshold

V

Output Undervoltage-Protection
Trip Threshold

With respect to unloaded output voltage 65 75 %

PGOOD Lower Trip Threshold

Measured at FB with respect to unloaded
output voltage, hysteresis = 1%

%

PGOOD Upper Trip Threshold

Measured at FB with respect to unloaded
output voltage, hysteresis = 1%

%

CURRENT LIMIT

ILIM Adjustment Range 0.5

V

Current-Limit Threshold (Fixed) V

LIMIT

V

PGND

- VLX, ILIM = V

CC

80 115 mV

V

ILIM

= 2.00V

240

Current-Limit Threshold
(Adjustable)

V

LIMIT

V

PGND

- V

LX

V

ILIM

= 0.50V 33 65

mV

Current-Limit Threshold
(Negative)

V

NEG

VLX - V

PGND

, SKIP = ILIM = V

CC

-85 mV

GATE DRIVERS

QSOP package 3.5

DH Gate-Driver On-Resistance
(Note 3)

R

DH

TQFN package 4.5

Ω

QSOP package 3.5

DL, high state

TQFN package 4.0

DL Gate-Driver On-Resistance
(Note 3)

R

DL

DL, low state 1.0

Ω

INPUTS AND OUTPUTS

Logic high 2.4
Logic low 0.4SHDN Input Level V

SHDN

No-fault mode 12 15

V

Logic Input High Voltage V

IH

D0–D5, SKIP, SUS 2.4 V

Logic Input Low Voltage V

IL

D0–D5, SKIP, SUS 0.8 V

High

V

CC

-

0.2

Open

REF

Four-Level Input Logic TON, S0, S1

GND 0.5

V

Note 2: On-time specifications are measured from 50% to 50% at the DH pin, with LX forced to 0, BST forced to 5V, and a 500pF

capacitor from DH to LX to simulate external MOSFET gate capacitance. Actual in-circuit times may be different due to
MOSFET switching speeds.

Note 3: Production testing limitations due to package handling require relaxed maximum on-resistance specifications for the thin

QFN package. The QSOP and thin QFN package contain the same die, and the thin QFN package imposes no additional
resistance in the circuit.

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

2.20 2.30

BST-LX forced to 5V

-17.5 -12.5

+12.5 +17.5

V

REF

160

-140

3.15 3.85

1.65 2.35

MAX8720

Dynamically Adjustable 6-Bit VID

Step-Down Controller

_______________________________________________________________________________________ 7

EFFICIENCY vs. LOAD CURRENT

(V

OUT

= 1.25V)

MAX8720 toc01

LOAD CURRENT (A)

EFFICIENCY (%)

1010.1

60

70

80

90

100

50

0.01 100

VIN = 12V

VIN = 20V

VIN = 7V

SKIP = GND
SKIP = V

CC

OUTPUT VOLTAGE vs. LOAD CURRENT

(V

OUT

= 1.25V)

MAX8720 toc02

LOAD CURRENT (A)

OUTPUT VOLTAGE (V)

15105

1.250

1.255

1.245
020

SKIP MODE

PWM MODE

SWITCHING FREQUENCY

vs. INPUT VOLTAGE

MAX8720 toc04

INPUT VOLTAGE (V)

FREQUENCY (kHz)

201510

290

300

310

320

330

340

350

360

280

525

I

OUT

= 18A

I

OUT

= 3A

SKIP = V

CC

NO-LOAD SUPPLY CURRENT

vs. INPUT VOLTAGE (PWM MODE)

MAX8720 toc05

INPUT VOLTAGE (V)

SUPPLY CURRENT (mA)

201510

5

10

15

20

25

30

0

525

ICC + I

DD

IIN

NO-LOAD SUPPLY CURRENT

vs. INPUT VOLTAGE (SKIP MODE)

MAX8720 toc06

INPUT VOLTAGE (V)

SUPPLY CURRENT (mA)

201510

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0

525

I

IN

ICC + I

DD

1.990

1.994

2.002

1.998

2.006

2.010

-20 200406080100

REFERENCE LOAD REGULATION

MAX8720 toc07

I

REF

(µA)

REFERENCE VOLTAGE (V)

Typical Operating Characteristics

(MAX8720 Circuit of Figure 1, VIN= 12V, VDD= VCC= 5V, TON = open, TA= +25°C, unless otherwise noted.)

SWITCHING FREQUENCY

vs. LOAD CURRENT

MAX8720 toc03

LOAD CURRENT (A)

SWITCHING FREQUENCY (kHz)

15105

100

200

300

400

0

020

PWM MODE

SKIP MODE

MAX8720

Dynamically Adjustable 6-Bit VID
Step-Down Controller

8 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(MAX8720 Circuit of Figure 1, VIN= 12V, VDD= VCC= 5V, TON = open, TA= +25°C, unless otherwise noted.)

2ms/div

V

CC

UVLO WAVEFORM

1.25V

MAX8720 toc10

0

0

0

5V

4V

A

B

C

D

I

OUT

= 1A

A = V

OUT

, 500mV/div

B = V

CC

, 2V/div

C = DL, 5V/div
D = PGOOD, 5V/div

20µs/div

LOAD TRANSIENT

(SKIP MODE)

1.25V

MAX8720 toc11

0

10A

0

0

12V

A

B

C

D

SKIP = GND, I

OUT

= 1A TO 11A TO 1A

A = V

OUT

, 50mV/div

B = LX, 10V/div

C = CONTROL, 5V/div
D = INDUCTOR CURRENT, 10A/div

20µs/div

LOAD TRANSIENT

(PWM MODE)

1.25V

MAX8720 toc12

0

10A

0

0

12V

A

B

C

D

SKIP = VCC, I

OUT

= 1A TO 11A TO 1A

A = V

OUT

, 50mV/div

B = LX, 10V/div

C = CONTROL, 5V/div
D = INDUCTOR CURRENT, 10A/div

50µs/div

DYNAMIC OUTPUT VOLTAGE TRANSITION

(SKIP MODE)

1.65V

MAX8720 toc13

0

10A

0

0

1.25V
12V

A

B

C

D

SKIP = GND, I

OUT

= 0.2A

A = V

OUT

, 200mV/div

B = LX, 10V/div

C = D4, 5V/div
D = INDUCTOR CURRENT, 10A/div

-10A

500µs/div

STARTUP WAVEFORMS (NO LOAD)

1.25V

MAX8720 toc08

0
0

0

0

5V

5A

-5A

A

B

C

D

I

OUT

= NO LOAD

A = V

OUT

, 500mV/div

B = PGOOD, 5V/div

C = SHDN, 5V/div
D = INDUCTOR CURRENT, 5A/div

500µs/div

STARTUP WAVEFORMS (HEAVY LOAD)

1.25V

MAX8720 toc09

0
0

0

0

5V

10A

A

B

C

D

I

OUT

= 10A

A = V

OUT

, 500mV/div

B = PGOOD, 5V/div

C = SHDN, 5V/div
D = INDUCTOR CURRENT, 10A/div

0

5

15

10

20

25

1.995

REFERENCE VOLTAGE DISTRIBUTION

MAX8720 toc18

REFERENCE VOLTAGE (V)

SAMPLE PERCENTAGE (%)

1.998 2.0052.0022.000

100

µs/div

SUSPEND TRANSITION

(SKIP MODE)

1.25V

MAX8720 toc15

0

10A

0

0

12V

A

B

C

D

SKIP = GND, I

OUT

= 0.2A

A = V

OUT

, 500mV/div

B = LX, 10V/div

C = D4, 5V/div
D = INDUCTOR CURRENT, 10A/div

-10A

0.65V

5V

0

5

15

10

20

25

-0.48

OUTPUT VOLTAGE DISTRIBUTION

MAX8720 toc17

OUTPUT VOLTAGE ERROR (%)

SAMPLE PERCENTAGE (%)

-0.24 0.480.240.00

V

OUT

= 1.25V

50µs/div

DYNAMIC OUTPUT VOLTAGE TRANSITION

(PWM MODE)

1.65V

MAX8720 toc14

0

10A

0

0

1.25V
12V

A

B

C

D

SKIP = VCC, I

OUT

= 0.2A

A = V

OUT

, 200mV/div

B = LX, 10V/div

C = D4, 5V/div
D = INDUCTOR CURRENT, 10A/div

-10A

100µs/div

SUSPEND TRANSITION

(PWM MODE)

1.25V

MAX8720 toc16

0

10A

0

0

12V

A

B

C

D

SKIP = VCC, I

OUT

= 0.2A

A = V

OUT

, 500mV/div

B = LX, 10V/div

C = D4, 5V/div
D = INDUCTOR CURRENT, 10A/div

-10A

0.65V

5V

MAX8720

Dynamically Adjustable 6-Bit VID

Step-Down Controller

_______________________________________________________________________________________ 9

Typical Operating Characteristics (continued)

(MAX8720 Circuit of Figure 1, VIN= 12V, VDD= VCC= 5V, TON = open, TA= +25°C, unless otherwise noted.)

MAX8720

Dynamically Adjustable 6-Bit VID
Step-Down Controller

10 ______________________________________________________________________________________

Pin Description

PIN

28 QSOP

36 THIN

QFN

NAME FUNCTION

133V+

Battery Voltage-Sense Connection. Connect V+ to input power source. V+ is used only
for PWM one-shot timing. DH on-time is inversely proportional to input voltage over a 2V
to 28V range.

234SHDN

Shutdown Control Input. Connect SHDN to V

CC

for normal operation. Connect SHDN to

GND to put the controller into its shutdown state. Forcing SHDN to 12V to 15V disables
both the overvoltage-protection and undervoltage-protection circuits and clears the fault
latch. Do not connect SHDN to >15V.

335TIME

Slew-Rate Adjustment Pin. Connect a resistor from TIME to GND to set the internal slew­rate clock. A 470kΩ to 22kΩ resistor sets the clock from 38kHz to 818kHz, f

SLEW

=

150kHz x 120kΩ / R

TIME

. To reduce inrush current, f

SLEW

= 150kHz x 120kΩ / 4 x R

TIME

during power-up and power-down transient.

41FB

Fast Feedback Input. Connect FB to the junction of the external inductor and output­capacitor node (Figure 1).

52FBS

Feed b ack Rem ote- S ense Inp ut. For nonvol tag e- p osi ti oned ci r cui ts, connect FBS to V

OU T

d i r ectl y at the l oad . FBS i nter nal l y connects to the i nteg r ator that fi ne tunes the D C outp ut
vol tag e. For vol tag e- p osi ti oned ci r cui ts, connect FBS d i r ectl y to FB near the IC to d i sab l e the
FBS r em ote- sense i nteg r ator am p l i fi er . To d i sab l e al l thr ee i nteg r ator am p l i fi er s, connect FBS
to V

C C

.

63CC

Integ r ator C ap aci tor C onnecti on. C onnect a 47p F to 1000p F ( 47p F typ ) cap aci tor fr om C C to
AGN D to set the i nteg r ati on ti m e constant. C C can b e l eft op en i f FBS i s connected to V

C C

.

7, 8 4, 5 S0, S1

S usp end - M od e V ol tag e- S el ect Inp ut. S 0 and S 1 ar e four - l evel d i g i tal i np uts that sel ect the
susp end - m od e V ID cod e for the susp end - m od e m ul ti p l exer i np uts. If S U S i s h i g h, the
susp end - m od e V ID cod e i s d el i ver ed to the D AC .

97V

CC

Anal og S up p l y Inp ut. C onnect to the system sup p l y vol tag e ( + 4.5V to + 5.5V ) thr oug h a ser i es
10Ω r esi stor . Byp ass V

C C

to anal og g r ound w i th a 1µF or g r eater cer am i c cap aci tor .

10 8 TON

On-Time Selection Control Input. This is a four-level input that sets the K-factor to
determine DH on-time. Connect TON to the following pins for the indicated operation:
GND = 1000kHz
REF = 550kHz
Open = 300kHz
V

CC

= 200kHz

11 9 REF

2.0V Reference Voltage Output. Bypass REF to analog ground with a 0.22µF or greater
ceramic capacitor. The reference can source up to 50µA for external loads. Loading REF
degrades output voltage accuracy according to the REF load regulation error.

12 10 ILIM

Current-Limit Adjustment. The PGND–LX current-limit threshold defaults to 100mV if ILIM
is connected to V

CC

. In adjustable mode, the current-limit threshold voltage is 1/10th the
voltage seen at ILIM over a 0.5V to 3.0V range. The logic threshold for switchover to the
100mV default value is approximately V

CC

- 1V. Connect ILIM to REF for a fixed 200mV

threshold.