MAXIM MAX8529 Technical data

General Description

The MAX8529 dual, synchronized, step-down controller
generates two outputs from input supplies ranging from

4.75V to 23V. Each output is adjustable from sub-1V
to 18V. Input voltage ripple and total RMS input ripple
current are reduced by synchronized 180-degree out-of­phase operation.

The switching frequency is adjustable from 600kHz to

1.5MHz with an external resistor. Alternatively, the con­troller can be synchronized to an external clock gener­ated to another MAX8529 or a system clock. One
MAX8529 can be set to generate an in-phase, or 90­degree out-of-phase, clock signal for synchronization
with additional controllers. This allows two controllers to
operate either as an interleaved two- or four-phase sys­tem with each output shifted by 90 degrees. These
devices also feature soft-start and soft-stop.

The MAX8529 eliminates the need for current-sense
resistors by utilizing the low-side MOSFET’s on-resis­tance as a current-sense element. This protects the
DC-to-DC components from damage during output
overload conditions or when output short circuit faults
without requiring a current-sense resistor. Adjustable
foldback current limit reduces power dissipation during
short-circuit conditions. The MAX8529 includes a
power-on reset output to signal the system when both
outputs reach regulation.

The MAX8529 is available in a 24-pin QSOP package. An
evaluation kit is available to speed designs.

Applications

xDSL Modems and Routers

DSP, ASIC, and FPGA Power Supplies

Set-Top Boxes

Broadband Routers

Features

♦ Low Output Noise in DSL Band

♦ Ceramic Input/Output Capacitors

♦ Step-Down or Step-Up/Step-Down Operation

♦ Four Output, 90-Degree Out-of-Phase Operation

(Using Two MAX8529s)

♦ Foldback Current Limit

♦ 4.75V to 23V Input Supply Range

♦ 0 to 18V Output Voltage Range (Up to 6A)

♦ > 90% Efficiency

♦ Fixed-Frequency PWM Operation

♦ Adjustable 600kHz to 1.5MHz Switching

Frequency

♦ External SYNC Input

♦ Clock Output for Master/Slave Synchronization

♦ Soft-Start and Soft-Stop
♦ RST Output with 140ms Minimum Delay

♦ Lossless Current Limit (No Sense Resistor)

MAX8529

1.5MHz Dual 180° Out-of-Phase

PWM Step-Down Controller with POR

________________________________________________________________ Maxim Integrated Products 1

Pin Configuration

Ordering Information

19-2696; Rev 1; 4/07

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

PART TEMP RANGE PIN-PACKAGE

MAX8529EEG -40°C to +85°C 24 QSOP

TOP VIEW

COMP2

FB2

ILIM2

REF

GND

SYNC

ILIM1

FB1

COMP1

1

2

3

4

5

V+

6

7

8

9

10

11

12

24

EN

23

DH2

22

LX2

21

BST2OSC

20

DL2

19

MAX8529

QSOP

V

L

18

PGND

17

DL1CKO

16

BST1

15

LX1

14

DH1

13

RST

MAX8529

1.5MHz Dual 180° Out-of-Phase
PWM Step-Down Controller with POR

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 +25V

PGND to GND .......................................................-0.3V to +0.3V

V

L

to GND ..................-0.3V to the lower of +6V and (V+ + 0.3V)

BST1, BST2 to GND ...............................................-0.3V to +30V

LX1 to BST1..............................................................-6V to +0.3V

LX2 to BST2..............................................................-6V to +0.3V

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

BST1

+ 0.3V)

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

BST2

+ 0.3V)

DL1, DL2 to PGND........................................-0.3V to (V

L

+ 0.3V)

CKO, REF, OSC, ILIM1, ILIM2,

COMP1, COMP2 to GND ..........................-0.3V to (V

L

+ 0.3V)

FB1, FB2, RST, SYNC, EN to GND...........................-0.3V to +6V

V

L

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

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

Continuous Power Dissipation (T

A

= +70°C)

24-Pin QSOP (derate 9.4mW/°C above +70°C)...........762mW

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

(V+ = 12V, EN = ILIM_ = VL, SYNC = GND, IVL= 0mA, PGND = GND, C

REF

= 0.22µF, CVL= 4.7µF (ceramic), R

OSC

= 10kΩ,

compensation components for COMP_ are from Figure 1, T

A

= -40°C to +85°C (Note 1), unless otherwise noted.)

PARAMETER CONDITIONS MIN TYP MAX UNITS

GENERAL
V+ Operating Range
V+ Operating Supply Current V

(Note 2) 4.75 23.00
V

= V+ (Note 2) 4.75 5.50

L

unloaded, no MOSFETs connected 4.0 4.8 7.0 mA

L

V+ Standby Supply Current EN = LX_ = FB_ = 0V R
Thermal Shutdown Rising temperature, typical hysteresis = 10°C 160 °C

Current-Limit Threshold PGND - LX_
V

REGULATOR

L

Output Voltage 5.5V < V+ < 23V, 1mA < I
V

Undervoltage Lockout

L

Trip Level

4.4 4.55 4.7 V

REFERENCE
Output Voltage I
Reference Load Regulation 0µA < I

= 0µA 1.98 2.00 2.02 V

REF

< 50µA 0 4 10 mV

REF

SOFT-START
Digital Ramp Period

Internal 6-bit DAC for one converter to ramp from 0V to

full scale (Note 3)

Soft-Start Steps 64 Steps
FREQUENCY

Low End of Range R
High End of Range R
DH_ Minimum Off-Time R

= 10kΩ 540 600 600 kHz

OSC

= 5kΩ 1020 1200 1380 kHz

OSC

= 5kΩ 110 160 ns

OSC

= 10kΩ 0.50 0.65 1.00 mA

OSC

ILIM_ = V
R
R

L

= 100kΩ 32 50 62

ILIM_

= 600kΩ 225 300 375

ILIM_

< 50mA 4.75 5 5.25 V

LOAD

75 100 125

1024

V

mV

DC-to-

DC

Clocks

MAX8529

1.5MHz Dual 180° Out-of-Phase

PWM Step-Down Controller with POR

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(V+ = 12V, EN = ILIM_ = VL, SYNC = GND, IVL= 0mA, PGND = GND, C

REF

= 0.22µF, CVL= 4.7µF (ceramic), R

OSC

= 10kΩ,

compensation components for COMP_ are from Figure 1, T

A

= -40°C to +85°C (Note 1), unless otherwise noted.)

Note 1: Specifications to -40°C are guaranteed by design and not production tested.
Note 2: Operating supply range is guaranteed by V

L

line regulation test. Connect V+ to VLfor 5V operation.

Note 3: Guaranteed by design and not production tested.

SYNC Range

SYNC Input Pulse Width (Note 3)
SYNC Rise/Fall Time (Note 3) 100 ns

PARAMETER

Internal oscillator nominal frequency must be set to half

of the SYNC frequency

CONDITIONS

High 100
Low 100

MIN TYP MAX UNITS

1000 2800 kHz

ERROR AMPLIFIER
FB_ Input Bias Current 250 nA
FB_ Input Voltage Set Point 0.99 1.00 1.01 V

FB_ to COMP_ Transconductance
DRIVERS

DL_, DH_ Break-Before-Make Time C
DH_ On-Resistance

DL_ On-Resistance

0°C to +85°C 1.25 1.8 2.70

-40°C to +85°C 1.2 1.8 2.9

= 5nF 30 ns

LOAD

Low 1.5 2.5
High 3 5
Low 0.6 1.5

High 3 5
LOGIC INPUTS (EN, SYNC)
Input Low Level Typical 15% hysteresis, V
Input High Level V
Input High/Low Bias Current V

= 5.5V 2.4 V

L

= 0 or 5.5V -1 +0.1 +1 µA

EN

= 4.75V 0.8 V

L

LOGIC OUTPUTS (CKO)
Output Low Level V
Output High Level V

= 5V, sinking 5mA 0.4 V

L

= 5V, sourcing 5mA 4.0 V

L

COMP_
Pulldown Resistance During

Shutdown and Current Limit

17 Ω
RST OUTPUT
Output-Voltage Trip Level

Output Low Level
Output Leakage V+ = V

Reset Timeout Period V

Both FBs must be over this to allow the reset timer to

start; there is no hysteresis

V

= 5V, sinking 3.2mA 0.4

L

V

= 1V, sinking 0.4mA 0.3

L

= 5V, V

L

= 1V 140 315 560 ms

FB_

RST

= 5.5V, V

= 1V 1 µA

FB

0.87 0.9 0.93 V

FB_ to Reset Delay FB_ overdrive from 1V to 0.85V 4 µs

ns

mS

Ω

Ω

V

MAX8529

1.5MHz Dual 180° Out-of-Phase
PWM Step-Down Controller with POR

4 _______________________________________________________________________________________

Typical Operating Characteristics

(Circuit of Figure 1, VIN= 6V, TA = +25°C, unless otherwise noted.)

EFFICIENCY vs. LOAD

MAX8529 toc01

LOAD (A)

EFFICIENCY (%)

10.1

10

20

30

40

50

60

70

80

90

100

0

10

OUT2

OUT1

OUTPUT VOLTAGE ACCURACY

vs. LOAD

MAX8529 toc02

LOAD (A)

OUTPUT VOLTAGE ACCURACY (%)

43

12

-0.5

0.5

0

1.0

-1.0
05

OUT2

OUT1

VL VOLTAGE ACCURACY

vs. LOAD CURRENT

MAX8529 toc03

LOAD CURRENT (mA)

V

L

VOLTAGE ACCURACY

10050

-1.5

-1.0

-0.5

0

0.5

-2.0
0150

SWITCHING FREQUENCY vs. R

OSC

MAX8529 toc04

R

OSC

(kΩ)

SWITCHING FREQUENCY (kHz)

86

800

1000

1200

1400

1600

600

410

LOAD TRANSIENT RESPONSE (OUTPUT 1)

MAX8529 toc05

10μs/div

0A

I

OUT1

1A/div

V

OUT1

50mV/div
AC-COUPLED

V

OUT2

50mV/div
AC-COUPLED

LOAD TRANSIENT RESPONSE (OUTPUT 2)

MAX8529 toc06

10μs/div

0A

I

OUT2

1A/div

V

OUT1

50mV/div
AC-COUPLED

V

OUT2

50mV/div
AC-COUPLED

SOFT-START AND SOFT-STOP WAVEFORM

MAX8529 toc07

400μs/div

0V

0V

V

OUT2

1V/div

V

OUT1

1V/div

5V

0V

EN

RESET TIMEOUT

MAX8529 toc08

100ms/div

V

OUT1

2V/div
0V

0V

0V

V

OUT2

2V/div

0V

EN

5V

V

RST

5V/div

OUT-OF-PHASE WAVEFORM

MAX8529 toc09

200ns/div

V

OUT2

10mV/div
AC-COUPLED

V

OUT1

10mV/div
AC-COUPLED

V

LX2

5V/div

V

LX1

5V/div
0V

0V

MAX8529

1.5MHz Dual 180° Out-of-Phase

PWM Step-Down Controller with POR

_______________________________________________________________________________________ 5

Typical Operating Characteristics (continued)

(Circuit of Figure 1, VIN= 6V, TA = +25°C, unless otherwise noted.)

EXTERNALLY SYNCHRONIZED

SWITCHING WAVEFORM

200ns/div

MAX8529 toc10

5V
V

SYNC

0V

5V
V

CKO

0V

V

LX1

5V/div
0V

V

OUT1

10mV/div
AC-COUPLED

CKO OUTPUT WAVEFORM

200ns/div

MAX8529 toc11

SYNC = GND

5V
V

CK0

0V

V

LX1

5V/div
0V

V

OUT1

10mV/div
AC-COUPLED

CKO OUTPUT WAVEFORM

SYNC = V

200ns/div

MAX8529 toc12

L

5V
V

CK0

0V

V

LX1

5V/div
0V

V

OUT1

10mV/div
AC-COUPLED

SHORT-CIRCUIT CURRENT FOLDBACK

AND RECOVERY

SHORT
V

OUT2

200μs/div

MAX8529 toc13

V

OUT1

50mV/div
AC-COUPLED

V

OUT2

1V/div

0V

I

OUT2

2A/div

0A

OUTPUT2 NOISE SPECTRUM

0

250

500

FREQUENCY (kHz)

MAX8529 toc14

400nV/√Hz

40nV/√Hz

4nV/√Hz

750 1000 1250

MAX8529

1.5MHz Dual 180° Out-of-Phase
PWM Step-Down Controller with POR

6 _______________________________________________________________________________________

Pin Description

PIN NAME FUNCTION

1 COMP2 Compensation Pin for Regulator 2 (REG2). Compensate REG2’s control loop as shown in Figure 1.

Feedback Input for Regulator 2 (REG2). Connect FB2 to a resistive-divider between REG2’s output

2 FB2

3 ILIM2

4 OSC

5 V+ Input Supply Voltage (4.75V to 23V)

6 REF 2V Reference Output. Bypass to GND with a 0.22µF or greater ceramic capacitor.

7 GND Analog Ground

8 CKO

9 SYNC

10 ILIM1

and GND to adjust the output voltage between 1V and 18V. To set the output voltage below 1V,
connect FB2 to a resistive voltage-divider from REF to REG2’s output (see the Setting the Output
Voltage section).

Current-Limit Adjustment for Regulator 2 (REG2). The PGND–LX2 current-limit threshold defaults to
100mV if ILIM2 is connected to V
REG2’s current-limit threshold (V
the Setting the Valley Current Limit section).

Oscillator Frequency Set Input. The controller generates the clock signal by dividing down the
oscillator, so the switching frequency equals half the synchronization frequency (f
Connect a resistor from OSC to GND (R
10kΩ) to 1500kHz (R
connected to SYNC. When using SYNC, set R

Clock Output. Clock Output for external 2- or 4-phase synchronization (see the Clock Synchronization
(SYNC, CKO) section).

Synchronization Input or Clock Output Selection Input. SYNC has three operating modes. Connect
SYNC to a 1200kHz to 2800kHz clock for external synchronization. Connect SYNC to GND for 2­phase operation as a master controller. Connect SYNC to V
controller (see the Clock Synchronization (SYNC, CKO) section).

Current-Limit Adjustment for Regulator 1 (REG1). The PGND–LX1 current-limit threshold defaults to
100mV if ILIM1 is connected to V
current-limit threshold (V
Setting the Valley Current Limit section).

= 4kΩ). The controller still requires R

OSC

ITH1

. Connect a resistor (R

L

) from 50mV (R

ITH2

OSC

. Connect a resistor (R

L

) from 50mV (R

ILIM2

= 100kΩ) to 300mV (R

ILIM2

) to set the switching frequency from 600kHz (R

for one half of the SYNC input.

OSC

for 4-phase operation as a master

L

ILIM1

= 100kΩ) to 300mV (R

ILIM1

) from ILIM2 to GND to adjust the

= 600kΩ) (see

ILIM2

= f

OSC

/ 2).

OSC

=

SW

when an external clock is

OSC

) from ILIM1 to GND to adjust REG1’s

= 600kΩ) (see the

ILIM1

Feedback Input for Regulator 1 (REG1). Connect FB1 to a resistive-divider between REG1’s output

11 FB1

12 COMP1 Compensation Pin for Regulator 1 (REG1). Compensate REG1’s control loop as shown in Figure 1.

13 RST

and GND to adjust the output voltage between 1V and 18V. To set the output voltage below 1V,
connect FB1 to a resistive voltage-divider from REF and REG1’s output (see the Setting the Output
Voltage section).

Open-Drain Reset Output. RST is low when either output voltage is more than 10% below its
regulation point. After soft-start is completed and both outputs exceed 90% of their nominal output
voltage (VFB_ > 0.9V), RST becomes high impedance after a 140ms delay and remains high
impedance as long as both outputs maintain regulation. Connect a resistor between RST and the
logic supply for logic-level voltages.