Rainbow Electronics MAX887 User Manual

_______________General Description

The MAX887 high-efficiency, step-down DC-DC con­verter provides an adjustable output from 1.25V to

10.5V. It accepts inputs from 3.5V to 11V and delivers
600mA. Operation to 100% duty cycle minimizes
dropout voltage (300mV typ at 500mA). Synchronous
rectification reduces output rectifier losses, resulting in
efficiency as high as 95%.

Fixed-frequency pulse-width modulation (PWM)
reduces noise in sensitive communications applica­tions. Using a high-frequency internal oscillator allows
tiny surface-mount components to reduce PC board
area, and eliminates audio-frequency interference. A
SYNC input allows synchronization to an external clock
to avoid interference with sensitive RF and data­acquisition circuits.

The MAX887 features current-mode operation for supe­rior load/line-transient response. Cycle-by-cycle current
limiting protects the internal MOSFET and rectifier. A
low-current (2.5µA typ) shutdown mode conserves bat­tery life.

________________________Applications

Portable Instruments
Cellular Phones and Radios
Personal Communicators
Distributed Power Systems
Computer Peripherals

____________________________Features

♦ 95% Efficiency
♦ 600mA Output Current
♦ Cycle-by-Cycle Current Limiting
♦ Low-Dropout, 100% Duty-Cycle Operation,

300mV at 500mA

♦ Internal 0.6Ω (typ) MOSFET
♦ Internal Synchronous Rectifier
♦ High-Frequency Current-Mode PWM
♦ External SYNC or Internal 300kHz Oscillator
♦ Guaranteed 260kHz to 340kHz Internal Oscillator

Frequency Limits

♦ 2.5µA Shutdown Mode

MAX887

100% Duty Cycle, Low-Noise,

Step-Down, PWM DC-DC Converter

________________________________________________________________

Maxim Integrated Products

1

1

2

8

7

V+

LX

SYNC

GND

SHDN

FB

REF

VL

MAX887

SO

TOP VIEW

3

4

6

5

__________________Pin Configuration

MAX887

REF

R1

165kΩ

R2

100kΩ

0.047µF

2.2µF

47µF

47µF

C1
100pF

0.33µF

33µH

V+ LX

FB

GND

SYNC
VL

SHDN

V

OUT

= 3.3V

V

OUT

= 1.25V (R1/R2 + 1)

V

IN

= 3.5V to 11V

ON

OFF

__________Typical Operating Circuit

19-1142 Rev 0; 9/96

PART

MAX887HC/D
MAX887HESA -40°C to +85°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

Dice*
8 SO

EVALUATION KIT MANUAL

AVAILABLE

______________Ordering Information

*

Contact factory for availability. Dice are tested at TA= +25°C.

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone]

100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter

ABSOLUTE MAXIMUM RATINGS

REF, FB, SYNC, VL to GND..................................... -0.3V to +6V

V+ to GND............................................................. -0.3V to +12V

SHDN, LX to GND ....................................... -0.3V to (V+ + 0.3V)

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

Continuous Power Dissipation (T

SO (derate 9.09mW/°C above +70°C) .........................471mW

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional

MAX887

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.

= +70°C)

A

ELECTRICAL CHARACTERISTICS

(V+ = +7V, PGND = GND = 0V, SHDN = V+, (TA= 0°C to T

Quiescent Supply Current
(PWM Mode)

Quiescent Supply Current
(PFM Mode)

Shutdown Supply Current
Output Voltage Range

PWM FB Feedback Threshold
FB Input Current
SYNC Frequency

PWM Switching Frequency
High-Side Current Limit
LX On-Resistance
LX Leakage Current

LX Reverse Leakage Current,
Regulator Off

Undervoltage Lockout
Startup Voltage
SYNC Input High Voltage
SYNC Input Low Voltage
SYNC Input Current

SHDN Input High Voltage
SHDN Input Low Voltage
SHDN Input Current, Sinking
SHDN Input Capacitance

VL Output Voltage V
REF Output Voltage V

Note 1: Guaranteed by design and not production tested.

V+, PWM

V+, PFM

V+, SHDN

OUT, RANGE

FB

FB

SYNC

OSC

LIM+

ON, LX

LXLKG

LXLKGR

+, UVLO
+, START
IH, SYNC

IL, SYNC

IN, SYNC

IH, SHDN

V

IL, SHDN

I

IN-, SHDN

C

IN, SHDN

L

REF

I

I
SHDN = GND

Circuit of Figure 2
I
VIN= 4V to 11V, PWM mode
SYNC = 3.0V, PWM duty cycle = 50%
FB = 1.30V

SYNC = 3.0V, FB = 1.18V
SYNC = 3.0V

ILX= ±100mA
V+ = 12V, LX = GND to 12V

V+ = floating, LX = 5V, SHDN = GND
V+ falling

V+ rising

SYNC = GND or 3V

SHDN = GND or V+
(Note 1) 10 pF
IVL= 0mA to 1mA 3.3 V
0µA to 30µA 1.25 V

MAX

= 0mA, SYNC = 3.0V

OUT

= 0mA, SYNC = GND

OUT

= 0mA to 500mA

OUT

Operating Temperature Ranges

MAX887HC/D.......................................................0°C to +70°C

MAX887HESA...................................................-40°C to +85°C

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

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

), unless otherwise noted.)

CONDITIONS

0.8 V
±1 µA

UNITSMIN TYP MAXSYMBOLPARAMETER

%/mA0.005Load Regulation

%/V0.2Line Regulation

kHz25 440f

kHz260 300 340f

V3.5 11.0V+Supply Range

mA2.7 4.0I

mA0.2 0.5I

µA2.5 5I

V1.25 10.50V

V1.225 1.250 1.275V

µA±0.10I

ns500SYNC, PWSYNC Pulse Width High or Low

%100PWM, DUTYPWM Maximum Duty Cycle

A0.75 1.0 1.40I
Ω0.6R

µA-10 1.0 10I
µA1.0 20I

V3.0 3.3V
V3.1 3.5V
V2.5V
V0.5V

µA±1I

V2.4V

2 _______________________________________________________________________________________

100% Duty Cycle, Low-Noise,

Step-Down, PWM DC-DC Converter

ELECTRICAL CHARACTERISTICS

(V+ = +7V, PGND = GND = 0V, SHDN = V+, (TA= -40°C to +85°C), unless otherwise noted.) (Note 2)

CONDITIONS

Quiescent Supply Current
(PWM Mode)

Quiescent Supply Current
(PFM Mode)

Shutdown Supply Current
Output Voltage Range
PWM FB Feedback Threshold
FB Input Current
PWM Switching Frequency
High-Side Current Limit
Undervoltage Lockout
Startup Voltage

V+, PWM

V+, PFM

V+, SHDN

OUT, RANGE

FB

FB

OSC

LIM+

+, UVLO

+, START

Note 2: Specifications from 0°C to -40°C are guaranteed by design and not production tested.

I

= 0mA, SYNC = 3.0V

OUT

I

= 0mA, SYNC = GND

OUT

SHDN = GND
Circuit of Figure 2
SYNC = 3.0V, PWM duty cycle = 50%
FB = 1.30V
SYNC = 3.0V

V+ falling
V+ rising

MAX887

UNITSMIN TYP MAXSYMBOLPARAMETER

V3.5 11.0V+Supply Range

mA2.7 4.0I

mA0.2 0.6I

µA2.5 5I

V1.25 10.50V
V1.222 1.250 1.278V

µA±0.10I

kHz250 300 350f

A0.75 1.00 1.50I
V3.0 3.3V
V3.1 3.5V

__________________________________________Typical Operating Characteristics

(Circuit of Figure 2, TA = +25°C, unless otherwise noted.)

DROPOUT VOLTAGE
vs. LOAD CURRENT

0.7

0.6

0.5

0.4

0.3

DROPOUT VOLTAGE (V)

0.2

0.1

0

0 200 400 600 800 1000

3.3V SETTING
= 3.135V

V

OUT

5V SETTING

= 4.75V

V

OUT

LOAD CURRENT (mA)

MAX887-01

EFFICIENCY vs. OUTPUT CURRENT



100

PWM MODE

90

(SYNC = VL)

= 3.3V

V

80
70
60
50
40

EFFICIENCY (%)

30
20
10

OUT

V

V

= 11V

IN

IN

= 9V

VIN = 4V


= 5V

V

IN

V

= 7V

IN



0

0.0001 0.001 0.01 0.1 0.6
OUTPUT CURRENT (A)

MAX887-02

EFFICIENCY (%)

EFFICIENCY vs. OUTPUT CURRENT

100

PWM MODE

90

(SYNC = VL)

80
70
60
50
40
30
20
10

0

0.0001 0.001 0.01 0.1 0.6

V

OUT

VIN = 7V


VIN = 5.5V

= 5V



VIN = 9V


= 11V

V

IN

OUTPUT CURRENT (A)

MAX887-03

_______________________________________________________________________________________ 3

100% Duty Cycle, Low-Noise,
Step-Down, PWM DC-DC Converter

____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 2, TA = +25°C, unless otherwise noted.)

EFFICIENCY vs. OUTPUT CURRENT

100

MAX887

EFFICIENCY (%)

VIN = 4V

90



80

VIN = 5V
70
60
50
40
30
20
10

0

0.0001 0.001 0.01 0.1 0.6

VIN = 9V

VIN = 7V


OUTPUT CURRENT (A)

MAXIMUM OUTPUT CURRENT

vs. SYNC FREQUENCY

1200

1000

800

600

400

200

MAXIMUM OUTPUT CURRENT (mA)

0

0 100 200 300 400 500 600



VIN = 11V

IDLE MODE

(SYNC = GND)

V

OUT

C2, C3 = 47µF
L1 = 33µH

= 5V

V

IN

= 3.3V

V

OUT

= -5% at I

V

OUT

SYNC FREQUENCY (kHz)

= 3.3V

OUT(MAX)

100

90

MAX887-04

80
70
60
50
40

EFFICIENCY (%)

30
20
10

0

0.0001 0.001 0.01 0.1 0.6

3.5

MAX887-07

3.0

2.5

2.0

1.5

1.0

QUIESCENT CURRENT (mA)

0.5

0

EFFICIENCY vs. OUTPUT CURRENT



VIN = 5.5V

VIN = 11V

VIN = 9V


VIN = 7V


OUTPUT CURRENT (A)

IDLE MODE

(SYNC = GND)

= 5V

V

OUT

QUIESCENT SUPPLY CURRENT

vs. SUPPLY VOLTAGE

A

A

A: V

= 3.3V, PWM MODE

OUT

= 3.3V, PFM MODE

B: V

OUT

C

B

024681012141618

SUPPLY VOLTAGE (V)

MAXIMUM OUTPUT CURRENT

1200

MAX887-05

1000

800

600

400

200

MAXIMUM OUTPUT CURRENT (mA)

MAX887-08

QUIESCENT CURRENT (mA)

GUARANTEED OUTPUT CURRENT
OF FIGURE 2 IS 600mA

0

357911131517

3.0
VIN = 5.3V

= 3.3V

V

OUT

2.5

2.0

1.5

1.0

0.5

0

-60 -40 -20 0 20 40 60 80 100 120 140

vs. SUPPLY VOLTAGE

3.3V SETTING, V

5V SETTING, V

SUPPLY VOLTAGE (V)

OUT

OUT

= 3.135V

= 4.75V

QUIESCENT CURRENT

vs.TEMPERATURE

PWM MODE

PFM MODE

TEMPERATURE (°C)

MAX887-06

MAX887-09

SWITCHING FREQUENCY

vs. SUPPLY VOLTAGE

350

V

= 3.3V

340
330
320
310
300
290
280
270

SWITCHING FREQUENCY (kHz)

260
250

OUT

024681012141618

SUPPLY VOLTAGE (V)

350
340

MAX887-10

330
320
310
300
290

FREQUENCY (kHz)

280
270
260
250

SWITCHING FREQUENCY

vs. TEMPERATURE

V

= 3.3V

OUT

-60 -40 -20 0 20 40 60 80 100 120 140
TEMPERATURE (°C)

MAX887-11

OUTPUT NOISE (mV)

OUTPUT RIPPLE AND HARMONICS

4

VIN = 5V

= 3.3V

V

OUT

= 500mA

I

3

OUT

PWM MODE

2

1

0

-1
10k  10M

100k 1M

FREQUENCY (Hz)

4 _______________________________________________________________________________________



MAX887 TOC-20