Rainbow Electronics MAX685 User Manual

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General Description

The MAX685 DC-DC converter provides low-noise dual outputs for powering CCD imaging devices and LCDs. This device uses a single inductor to provide independently regulated positive and negative outputs. Integrated power switches are included in the small 16-pin QSOP package (same size as an 8-pin SO) to save space and reduce cost.

Each output delivers up to 10mA from a +2.7V to +5.5V input voltage range. Output voltages are set independently up to 24V and down to -9V. With a few additional low-cost components, the output voltages can be set at up to 45V and down to -16V. Output ripple magnitude is 30mVp-p. The MAX685 uses a fixed-frequency, pulsewidth-modulated (PWM) control scheme at 220kHz or 400kHz to permit output noise filtering and to reduce the size of external components. The frequency can also be synchronized to an external clock signal between 200kHz and 480kHz.

The MAX685 has a power-OK indicator output (POK) that signals when both outputs are within regulation. A logic-controlled shutdown completely turns off both outputs and reduces supply current to 0.1µA. The user can also set which output turns on first.

The preassembled MAX685 evaluation kit is available to reduce design time.

Applications

Camcorders LCDs Digital Cameras CCD Imaging Devices Notebooks

Features

♦ Dual Output Using a Single Inductor ♦ Low-Noise Output, 30mVp-p Ripple ♦ Output Voltages up to 24V and down to -9V

(up to 45V and down to -16V with added components)

♦ Internal Switches in a Small Package ♦ 220kHz/400kHz Fixed-Frequency PWM Operation ♦ Frequency Can Be Synchronized to

External Clock

♦ Power-OK Indicator ♦ Selectable Power-On Sequencing ♦ 0.1µA Logic-Controlled Shutdown

MAX685

Dual-Output (Positive and Negative),

DC-DC Converter for CCD and LCD

________________________________________________________________

Maxim Integrated Products

MAX685

VP V

OFF

INPUT

2.7V TO 5.5V LXN

FBP

LXP

FBN

REFGND

NEGATIVE OUTPUT DOWN TO -9V, 10mA

POSITIVE OUTPUT UP TO 24V, 10mA

SHDN

SYNC

SEQ

POK

POS

NEG

OPTIONAL

POWER-OK INDICATOR

Typical Operating Circuit

19-1353; Rev 0; 4/98

PART

MAX685EEE -40°C to +85°C

TEMP. RANGE PIN-PACKAGE

16 QSOP

EVALUATION KIT

AVAILABLE

Pin Configuration

Ordering Information

TOP VIEW

16 15

I.C.

PGND

FBP REF

11 10

FBN

GND

LXP LXN

I.C.

I.C. = INTERNALLY CONNECTED

3 4

POK SEQ

SHDN

6 7

SYNC

MAX685

QSOP

MAX685

Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VDD= VP = 5V, TA= 0°C to +85°C unless otherwise noted. Typical values are at TA= +25°C.)

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.

VDD, VP to GND........................................................-0.3V to +6V

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

to VP...............................................................-0.3V to +0.3V

LXN, POK to GND ..................................................-0.3V to +30V

LXP to V

..............................................................-15V to +0.3V

REF, SEQ,

SHDN to GND...........................-0.3V to (VDD+ 0.3V)

FBP, FBN, SYNC to GND .........................................-0.3V to +6V

Continuous Power Dissipation (T

= +70°C)

16-Pin QSOP (derate 8.3mW/°C above +70°C)............667mW

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

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

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

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

2.7V < VDD< 5.5V

VDD= 5.5V (Note 1)

No load

VDD= VP

No load

C3 = C4 = 10µF, I

LOAD

= 5mA

OUT

= 0 to 10mA, C1 = 10µF

VDD= rising

VDD= 4.5V to 5.5V

FBP

= 1.35V, V

FBN

= -0.1V

VDD= 4.5V, V

OUT+

≥ 14.25V, V

OUT-

≤ -7.125V,

Figure 3 TA= +25°C VDD= 4.5V

SYNC = SEQ = SHDN = GND

SYNC = V

CONDITIONS

µA0.1 1Input Bias Current

V0.7 x V

Logic-High Input

V0.3 x V

Logic-Low Input

µA±0.01 ±0.1FBP, FBN Input Leakage Current

mV-16 10 36FBN Threshold Voltage

V1.21 1.24 1.27FBP Threshold Voltage

mV50UVLO Hysteresis

V2.35 2.5 2.65UVLO Threshold

µA0.1 10Shutdown Supply Current

V-9 -1.27Negative Output Voltage Range

VVP 24

V2.7 5.5Input Voltage Range

Positive Output Voltage Range

mVp-p30Output Voltage Ripple

%/mA0.13Load Regulation

%/V0.2Line Regulation

µA300 500Idle Quiescent Current

mA10Output Current mA440LX Current Limit

Ω0.6 2LXP, LXN On-Resistance

mA0.8Quiescent Current

UNITSMIN TYP MAXPARAMETER

0 < I

REF

< 50µA

No load

mV-2V

REF

Load Regulation

V1.23 1.250 1.27V

REF

Output Voltage

SHUTDOWN (SHDN)

UNDERVOLTAGE LOCKOUT

REFERENCE VOLTAGE

FB INPUTS

LOGIC INPUTS (SEQ, SHDN, SYNC)

MAX685

Dual-Output (Positive and Negative),

DC-DC Converter for CCD and LCD

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VDD= VP = 5V, TA= 0°C to +85°C unless otherwise noted. Typical values are at TA= +25°C.)

ELECTRICAL CHARACTERISTICS

(VDD, VP = 5V, TA= -40°C to +85°C unless otherwise noted.) (Note 2)

Note 1: Negative output voltage can be larger magnitude for lower values of V

. The voltage between VDDand V

OUT-

must not

exceed 14.5V.

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

VDD= 5.5V (Note 1)

VDD= VP

No load

VDD= rising

VIN= 4.5V, V

OUT+

≥ 14.25V, V

OUT-

≤ -7.125V,

Figure 3 SYNC = GND

SYNC = SEQ = SHDN = GND

CONDITIONS

V-9 -1.27Negative Output Voltage Range

VVP 24

V2.7 5.5Input Voltage Range

Positive Output Voltage Range

V1.205 1.275FBP Threshold Voltage

V2.35 2.65UVLO Threshold

mA10Maximum Output Current

µA500Idle Quiescent Current

µA10Shutdown Supply Current

UNITSMIN MAXPARAMETER

CONDITIONS

SYNC = V

SYNC = GND

kHz

320 400 480

Oscillator Frequency (internal)

175 220 265

kHz200 480Sync Frequency Range (external)

POK

= 2mA

FBN falling

FBP rising

V0.4POK Output Low Voltage

UNITSMIN TYP MAX

54 79 108

PARAMETER

FBN POK Threshold

V1.090 1.122 1.150FBP POK Threshold

POK

= 10V µA1POK Output Off Current

2.7V < VDD≤ 5.5V

No load

V0.3 x V

Logic-Low Input

mV-20 40FBN Threshold Voltage

2.7V < VDD≤ 5.5V V0.7 x V

Logic-High Input

FBP rising V1.090 1.150FBP POK Threshold FBN falling mV54 108FBN POK Threshold

SYNC INPUT

POK COMPARATORS

No load V1.225 1.275VREF Output Voltage

SHUTDOWN

UNDERVOLTAGE LOCKOUT

FB INPUTS AND REFERENCE VOLTAGE

LOGIC INPUTS (SEQ, SHDN, SYNC)

POK COMPARATORS

1.240

1.242

1.244

1.248

1.246

1.250

1.252

1.254

-40 200-20 40 60 80 100

REFERENCE VOLTAGE

vs. TEMPERATURE

MAX685-13

TEMPERATURE (°C)

REFERENCE VOLTAGE (V)

VIN = 5.0V

VIN = 3.3V

MAX685

Dual-Output (Positive and Negative), DC-DC Converter for CCD and LCD

4 _______________________________________________________________________________________

0 42 6 8 10

EFFICIENCY vs. LOAD CURRENT

(POSITIVE OUTPUT LOADED)

MAX685-01

LOAD CURRENT (mA)

EFFICIENCY (%)

VIN = 5.0V

VIN = 3.3V

0 42 3 51 6 7 98 10

EFFICIENCY vs. LOAD CURRENT

(NEGATIVE OUTPUT LOADED)

MAX685-02

LOAD CURRENT (mA)

EFFICIENCY (%)

VIN = 5.0V

VIN = 3.3V

75 70

85 80

0 42 6 8 10

EFFICIENCY vs. LOAD CURRENT

(BOTH OUTPUTS LOADED)

MAX685-03

LOAD CURRENT (mA)

EFFICIENCY (%)

VIN = 5.0V

VIN = 3.3V

0.5

1.0

1.5

2.0

2.5 3.53.0 4.0 4.5 5.0 5.5

NO-LOAD CURRENT vs.

INPUT VOLTAGE

MAX685-04

INPUT VOLTAGE (V)

NO-LOAD CURRENT (mA)

150

180 170 160

190

200

210

220

230

240

250

2.7 3.73.2 4.2 4.7 5.2 5.7

LX SWITCHING FREQUENCY

vs. INPUT VOLTAGE

MAX865-07

INPUT VOLTAGE (V)

OSCILLATOR FREQUENCY (kHz)

SYNC = V

1.248

1.249

1.250

0 15 205 10 25 30 35 40 45 50

REFERENCE LOAD REGULATION

MAX685-06

LOAD CURRENT (µA)

REFERENCE VOLTAGE (V)

Typical Operating Characteristics

(Circuit of Figure 3, V

OUT+

= 15V, V

OUT-

= -7.5V, TA= +25°C, unless otherwise noted.)

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