Rainbow Electronics MAX8625A User Manual

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.

General Description

The MAX8625A PWM step-up/down regulator is intend­ed to power digital logic, hard disk drives, motors, and
other loads in portable, battery-powered devices such
as PDAs, cell phones, digital still cameras (DSCs), and
MP3 players. The MAX8625A provides either a fixed

3.3V or adjustable output voltage (1.25V to 4V) at up to

0.8A from a 2.5V to 5.5V input. The MAX8625A utilizes
a 2A peak current limit.

Maxim’s proprietary H-bridge topology* provides a
seamless transition through all operating modes without
the glitches commonly seen with other devices. Four
internal MOSFETs (two switches and two synchronous
rectifiers) with internal compensation minimize external
components. A SKIP input selects a low-noise, fixed­frequency PWM mode, or a high-efficiency skip mode
where the converter automatically switches to PFM
mode under light loads for best light-load efficiency.
The internal oscillator operates at 1MHz to allow for a
small external inductor and capacitors.

The MAX8625A features current-limit circuitry that shuts
down the IC in the event of an output overload. In addi­tion, soft-start circuitry reduces inrush current during
startup. The IC also features True Shutdown

TM

, which
disconnects the output from the input when the IC is
disabled. The MAX8625A is available in a 3mm x 3mm,
14-pin TDFN package.

Applications

PDAs and Smartphones

DSCs and Camcorders

MP3 Players and Cellular Phones

Battery-Powered Hard Disk Drive (HDD)

Features

♦ Four Internal MOSFET True H-Bridge Buck/Boost
♦ Glitch-Free, Buck-Boost Transitions
♦ Minimal Output Ripple Variation on Transitions
♦ Up to 92% Efficiency

♦ 37µA (typ) Quiescent Current in Skip Mode

♦ 2.5V to 5.5V Input Range
♦ Fixed 3.3V or Adjustable Output

♦ 1µA (max) Logic-Controlled Shutdown

♦ True Shutdown
♦ Output Overload Protection
♦ Internal Compensation
♦ Internal Soft-Start
♦ 1MHz Switching Frequency
♦ Thermal-Overload Protection
♦ Small 3mm x 3mm, 14-Pin TDFN Package

MAX8625A

High-Efficiency, Seamless Transition,

Step-Up/Down DC-DC Converter

________________________________________________________________

Maxim Integrated Products

1

Ordering Information

Typical Operating Circuit

19-1006; Rev 1; 5/08

*

US Patent #7,289,119.

True Shutdown is a trademark of Maxim Integrated Products, Inc.

EVALUATION KIT

AVAILABLE

Note: The device is specified over the -40°C to +85°C extended
temperature range.

+

Denotes a lead-free package.

**

EP = Exposed pad.

Pin Configuration

PART

MAX8625AETD+

PIN­PACKAGE

14 TDFN-EP**
(3mm x 3mm)

TOP MARK

ABQ

TOP VIEW

IN

GND

GNDLX2

MAX8625A

LX2

OUT

ON

OUTSKIP

REFFB

9

8

EP

6

7

INLX1

14

13 11 10

12

+

245

1

3

LX1

EP = EXPOSED PAD.

TDFN-EP

OFF

INPUT

2.7V TO 5.5V

PWM

SKIP

ON

LX1

IN

MAX8625A

SKIP

ON

LX2

OUT

GND

FB

REF

OUTPUT

3.3V

MAX8625A

High-Efficiency, Seamless Transition,
Step-Up/Down DC-DC Converter

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VIN= 3.6V, ON = SKIP = IN, FB = GND, V

OUT

= 3.3V, LX_ unconnected, C

REF

= C5 = 0.1µF to GND, Figure 4. TA= -40°C to +85°C.

Typical values are at T

A

= +25°C, unless otherwise noted.) (Note 2)

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.

IN, OUT, SKIP, ON to GND ......................................-0.3V to +6V

REF, FB, to GND...............................................-0.3V, (IN + 0.3V)

LX2, LX1 (Note 1).........................................................±1.5A

RMS

Continuous Power Dissipation (TA= +70°C)

Single-Layer Board (derate 18.5mW/°C

above T

A

= +70°C) ...................................................1482mW

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

Note 1: LX1 and LX2 have internal clamp diodes to IN, PGND and OUT, PGND, respectively. Applications that forward bias these

diodes should take care not to exceed the device's power-dissipation limits.

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Range V

UVLO Threshold UVLO VIN rising, 60mV hysteresis 2.20 2.49 V

Quiescent Supply Current, FPWM
Mode, Switching

Quiescent Supply Current, Skip
Mode, Switching

Quiescent Supply Current, No
Switching, Skip Mode

Shutdown Supply Current I

Output Voltage Accuracy
(Fixed Output)

Output Voltage Range
(Adjustable Output)

Maximum Output Current VIN = 3.6V 0.80 A

Soft-Start L = 3.3µH; C

Load Regulation I

Line Regulation VIN = 2.5V to 5.5V 0.03 %/V

OUT Bias Current I

REF Output Voltage V

REF Load Regulation I

FB Feedback Threshold V

IN

I

IN

I

IN

I

IN

IN

OUT

REF

FB

No load, V

SKIP = GND, no load 37 µA

SKIP = GND, FB = 1.3V 35 45 µA

ON = GND, TA = +25°C 0.1 1

TA = +85°C 0.2

PWM mode, VIN = 2.5V to 5.5V 3.30 V

I

OUT

T

A

SKIP mode, valley regulation value 3.28 V

Average skip voltage 3.285

Load step +0.5A -3 %

OUT

V

OUT

VIN = 2.5V to 5.5V 1.244 1.25 1.256 V

REF

I

OUT

to 5.5V

OUT

= 0 to 0.5A, VIN = 2.5V to 5.5V,

= -40°C to +85°C (Note 3)

= 0 to 500mA 0.1 %/mA

= 3.3V 3 µA

= 10µA 1 mV

= 0 to full load, PWM mode; VIN = 2.5V

2.5 5.5 V

= 3.2V 15 22 mA

-1 +1 %

1.25 4.00 V

= C3 + C4 = 44µF 250 mA/ms

OUT

1.244 1.25 1.258 V

µA

MAX8625A

High-Efficiency, Seamless Transition,

Step-Up/Down DC-DC Converter

_______________________________________________________________________________________ 3

Note 2: Devices are production tested at TA= +25°C. Specifications over the operating temperature range are guaranteed by

design and characterization.

Note 3: Limits are guaranteed by design and not production tested.
Note 4: The idle-mode current threshold is the transition point between fixed-frequency PWM operation and idle-mode operation.

The specification is given in terms of output load current for an inductor value of 3.3µH. For the step-up mode, the idle-mode
transition varies with input to the output-voltage ratios.

ELECTRICAL CHARACTERISTICS (continued)

(VIN= 3.6V, ON = SKIP = IN, FB = GND, V

OUT

= 3.3V, LX_ unconnected, C

REF

= C5 = 0.1µF to GND, Figure 4. TA= -40°C to +85°C.

Typical values are at T

A

= +25°C, unless otherwise noted.) (Note 2)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

FB Dual-Mode Threshold V

FB Leakage Current I

ON, SKIP Input High Voltage V
ON, SKIP Input Low Voltage V

ON Input Leakage Current I

SKIP Input Leakage Current

Peak Current Limit I

Fault Latch-Off Delay 100 ms

MOSFET On-Resistance R

Rectifier-Off Current Threshold I

Idle-Mode Current Threshold
(Note 4)

LX1, LX2 Leakage Current I

Out Reverse Current I

Minimum T

OSC Frequency F

Thermal Shutdown 15°C hysteresis +165 °C

ON

T

FBDM

FB

IHL

I

SKIPH

I

SKIPL

LIMP

ON

LX1OFF

I

SKIP

LXLKG

LXLKGR

ONMIN

OSCPWM

VFB = 1.3V, TA = +25°C 0.001 0.1

VFB = 1.3V, TA = +85°C 0.01

2.5V < VIN < 5.5V 1.6 V

IH

2.5V < VIN < 5.5V 0.45 V

IL

2.5V < VIN < 5.5V, TA = +25°C 0.001 1

TA = +85°C 0.01

V

= 3.6V 3 12

SKIP

V

= 0V -2 -0.2

SKIP

LX1 PMOS 1700 2000 2300 mA

Each MOSFET, TA = +25°C 0.05 0.1

Each MOSFET, VIN = 2.5V to 5.5V,
T

= -40°C to +85°C

A

SKIP = GND 125 mA
SKIP = GND, load decreasing 100

Load increasing 300

VIN = V
V

= 0V to V

LX2

TA = +85°C 0.2

VIN = V
measure I (LX2), T

TA = +85°C 0.5

OUT

LX1

= V

= 5.5V, V

, TA = +25°C

OUT

= 0V, V

LX2

A

= 0V to VIN,

LX1

OUT

= +25°C

75 100 125 mV

0.2

0.01 1

= 5.5V,

850 1000 1150 kHz

0.01 1

25 %

µA

µA

µA

Ω

mA

µA

µA

Typical Operating Characteristics

(VIN= 3.6V, SKIP = GND, TA= +25°C, Figure 4, unless otherwise noted.)

MAX8625A

High-Efficiency, Seamless Transition,
Step-Up/Down DC-DC Converter

4 _______________________________________________________________________________________

EFFICIENCY vs. LOAD CURRENT

SKIP AND FPWM MODES

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 1000
LOAD CURRENT (mA)

EFFICIENCY vs. LOAD CURRENT

FPWM MODE (FIGURE 3)

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 1000
LOAD CURRENT (mA)

SKIP-MODE EFFICIENCY

100

95

MAX8625A toc01

V

= 3.3V

OUT

= 2.7V

V

IN

3.0V,

3.3V,

3.6V,

4.2V,

5.0V

100101

90

85

80

75

EFFICIENCY (%)

70

65

60

2.0 3.0 3.52.5 4.0 4.5 5.0 5.5 6.0

vs. INPUT VOLTAGE

300mA

500mA

INPUT VOLTAGE (V)

100mA

V

= 3.3V

OUT

LOAD CURRENT = 100mA,
300mA, 500mA

MAX8625A toc02

EFFICIENCY (%)

OUTPUT VOLTAGE (3.3V INTERNAL FB)

vs. LOAD CURRENT

2.0

1.5

MAX8625A toc04

1.0

0.5

V

= 3.45V

OUT

= 2.7V

V

IN

3.0V,

3.3V,

3.6V,

4.2V,

5.0V

100101

0

DEVIATION (%)

-0.5

-1.0

-1.5

V

= 3.3V

OUT

= +25°C, TA = -40°C, TA = +85°C,

T

A

-2.0

0.1 1000
LOAD CURRENT (mA)

100101

MAX8625A toc05

DEVIATION (%)

EFFICIENCY vs. LOAD CURRENT

FPWM MODE (FIGURE 3)

100

90

80

70

60

50

40

30

20

10

0

0.1 1000
LOAD CURRENT (mA)

V

OUT

V

100101

OUTPUT VOLTAGE (2.8V EXTERNAL FB)

vs. LOAD CURRENT (FIGURE 3)

2.0

1.5

1.0

0.5

0

-0.5

-1.0

V

-1.5

-2.0

= 2.8V

OUT

= +25°C, TA = -40°C, TA = +85°C

T

A

0.1 1000
LOAD CURRENT (mA)

100101

= 2.8V
= 2.7V

IN

3.0V,

3.3V,

3.6V,

4.2V,

5.0V

MAX8625A toc03

MAX8625A toc06

OUTPUT VOLTAGE vs. INPUT VOLTAGE

WITH INTERNAL FB RESISTORS

3.33

3.32

3.31

3.30

3.29

OUTPUT VOLTAGE (V)

3.28

LOAD: 500mA, V

= +25°C, TA = -40°C, TA = +85°C

T

A

3.27

3.0 4.0 4.53.5 5.0 5.5 6.0

= 3.3V

OUT

INPUT VOLTAGE (V)

MAX8625A toc07

OUTPUT VOLTAGE (V)

OUTPUT VOLTAGE vs. INPUT VOLTAGE

WITH EXTERNAL FB RESISTORS

2.82

2.81

2.80

2.79

2.78

2.77

2.76

LOAD: 500mA, V

= +25°C, TA = -40°C, TA = +85°C (FIGURE 3)

T

A

2.75

3.0 4.0 4.53.5 5.0 5.5 6.0

= 2.8V

OUT

INPUT VOLTAGE (V)

MAX8625A toc08

SUPPLY CURRENT vs. INPUT VOLTAGE

WITH NO LOAD

100

FPWM MODE

10

1

SUPPLY CURRENT (mA)

0.1

0.01

2.0 6.0
INPUT VOLTAGE (V)

NO LOAD V

OUT

MAX8625A toc09

= 3.3V

5.55.04.54.03.53.02.5

Typical Operating Characteristics (continued)

(VIN= 3.6V, SKIP = GND, TA= +25°C, Figure 4, unless otherwise noted.)

MAX8625A

High-Efficiency, Seamless Transition,

Step-Up/Down DC-DC Converter

_______________________________________________________________________________________

5

MAXIMUM LOAD CURRENT

1000

900

800

700

600

500

400

300

MAXIMUM LOAD CURRENT (mA)

200

100

0

2.0 3.0 3.52.5 4.0 4.5 5.0 5.5 6.0

V

V

LX1

2V/div

vs. INPUT VOLTAGE

INPUT VOLTAGE (V)

SWITCHING WAVEFORMS

= 3.3V, LOAD = 500mA, V

IN

V

OUT

= 3.3V

= 3.3V

OUT

MAX8625A toc12

MAX8625A toc10

V

OUT

50mV/div
(AC-COUPLED)

SWITCHING WAVEFORMS

= 3V, LOAD = 500mA, V

V

IN

V

LX1

2V/div

V

LX2

2V/div

SWITCHING WAVEFORMS

= 3.6V, LOAD = 500mA, V

V

IN

V

LX1

2V/div

1

μs/div

OUT

MAX8625A toc11

OUT

MAX8625A toc13

= 3.3V

= 3.3V

V

OUT

50mV/div
(AC-COUPLED)

I

LX

500mA/div

V

OUT

50mV/div
(AC-COUPLED)

CH1 = V

CH2 = V

V

2V/div

2V/div

2V/div

LX2

I

LX

500mA/div

1

μs/div

SKIP MODE

= 3V, LOAD = 20mA,

V

IN

= 3.288V

V

OUT

LX1

LX2

10μs/div

MAX8625A toc14

V

OUT

20mV/div
(AC-COUPLED)

I

LX

500mA/div

V

2V/div

V

2V/div

V

2V/div

LX2

I

LX

500mA/div

1

μs/div

FPWM MODE

= 3V, LOAD = 20mA,

V

IN

= 3.308V

V

OUT

LX1

LX2

1μs/div

MAX8625A toc15

OUT

20mV/div
(AC-COUPLED)

I

LX

500mA/div