MAX8614BETD+TCK5 скачать даташит

MAX8614BETD+TCK5 скачать даташит

19-4014; Rev 1; 9/06

EVALUATION KIT

AVAILABLE

General Description

The MAX8614A/MAX8614B dual-output step-up DC-DC converters generate both a positive and negative supply voltage that are each independently regulated. The positive output delivers up to 50mA while the inverter supplies up to 100mA with input voltages between 2.7V

and 5.5V. The MAX8614A/MAX8614B are ideal for powering CCD imaging devices and displays in digital cameras and other portable equipment.

The MAX8614A/MAX8614B generate an adjustable positive output voltage up to +24V and a negative output down to 16V below the input voltage. The

MAX8614B has a higher current limit than the

MAX8614A. Both devices operate at a fixed 1MHz frequency to ease noise filtering in sensitive applications and to reduce external component size.

Additional features include pin-selectable power-on sequencing for use with a wide variety of CCDs, True

Shutdown™, overload protection, fault flag, and internal soft-start with controlled inrush current.

The MAX8614A/MAX8614B are available in a spacesaving 3mm x 3mm 14-pin TDFN package and are specified over the -40°C to +85°C extended temperature range.

Applications

CCD Bias Supplies and OLED Displays

Digital Cameras

Camcorders and Portable Multimedia

PDAs and Smartphones

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

Pin Configuration

Dual-Output (+ and -) DC-DC

Converters for CCD

Features

Dual Output Voltages (+ and -)

Adjustable Up to +24V and Down to -10V at 5.5V

IN

Output Short/Overload Protection

True Shutdown on Both Outputs

Controlled Inrush Current During Soft-Start

Selectable Power-On Sequencing

Up to 90% Efficiency

1µA Shutdown Current

1MHz Fixed-Frequency PWM Operation

Fault-Condition Flag

Thermal Shutdown

Small, 3mm x 3mm, 14-Pin TDFN Package

Ordering Information

PART

TEMP

RANGE

PIN-

PACKAGE

TOP

MARK

ILIM

BST/

INV

PK G

C O D E

MAX8614AETD+

-40°C to

+85°C

14 TD FN

3m m x 3m m

( T1433- 2)

ABG

MAX8614BETD+

-40°C to

+85°C

14 TD FN

3m m x 3m m

( T1433- 2)

ABH

+Denotes lead-free package.

0.44/

0.33

0.8/

0.75

T1433+

T1433+

Typical Operating Circuit

INPUT

(2.7V TO 5.5V)

V

INV

-7.5V

TOP VIEW

14 13 12 11 10 9

8

V

CC

ONINV

ONBST

AV

CC

MAX8614A

MAX8614B

REF

LXN

FBN

PVP

REF

AV

CC

MAX8614A

MAX8614B

+

1 2 3 4 5 6 7

SEQ

FLT

GND PGND

LXP

FBP

V

BST

+15V

TDFN

________________________________________________________________ Maxim Integrated Products 1

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.

Dual-Output (+ and -) DC-DC

Converters for CCD

ABSOLUTE MAXIMUM RATINGS

V

CC

, AV

CC to GND ...................................................-0.3V to +6V

LXN to V

CC

.............................................................-18V to +0.3V

LXP to PGND ..........................................................-0.3V to +33V

REF, ONINV, ONBST, SEQ, FBN, FBP

FLT to GND ..........................................-0.3V to (AV

CC

+ 0.3)V

PVP to GND ................................................-0.3V to (V

CC

+ 0.3)V

AV

CC to V

CC

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

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

Continuous Power Dissipation (T

A

= +70°C Multilayer Board)

14-Pin 3mm x 3mm TDFN (derate 18.2mW/°C above

T

A

= +70°C) ............................................................1454.4mW

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

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.

ELECTRICAL CHARACTERISTICS

(V

CC

= V

AVCC

= V

ONINV =

V

ONBST

= 3.6V, PGND = SEQ = GND, C6 = 0.22µF, C1 = 2.2µF, C2 = 4.7µF, Figure 1, T

A

= 0°C to +85°C, unless otherwise noted. Typical values are at T

A

= +25°C.)

CONDITIONS TYP PARAMETER

AV

CC

and V

CC

Voltage Range

UVLO Threshold

UVLO Hysteresis

(Note 1)

V

CC

rising

MIN

2.7

2.42

2.55

25

MAX

5.5

2.66

UNITS

V

V mV

Step-Up Output Voltage Adjust Range V

AVCC

24 V

Inverter Output Voltage Adjust Range

LXP Current Limit

LXP Short-Circuit Current Limit

LXN Current Limit

LXN On-Resistance

LXP On-Resistance

PVP On-Resistance

Maximum Duty Cycle

Quiescent Current (Switching, No Load)

Quiescent Current (No Switching, No Load)

Shutdown Supply Current

FBP Line Regulation

FBN Line Regulation

V

INV

- V

CC

(Note 2)

MAX8614B

MAX8614A

MAX8614B

MAX8614A

MAX8614B

MAX8614A

V

CC

= 3.6V

V

CC

= 3.6V

V

CC

= 3.6V

Step-up and inverter

I

AVCC

I

VCC

I

AVCC

IV

CC

T

A

= +25°C

T

A

= +85°C

V

CC

= 2.7V to 5.5V

V

CC

= 2.7V to 5.5V

-16

0.7

0.34

0.90

0.52

0.65

0.28

82

0.8

90

0.75

2

400

8

0.1

0.1

-20

0.44

1.05

0.61

0.75

0.33

0.6

0.625

0.15

20

0

0.9

0.52

1.20

0.70

0.85

0.38

1.1

0.3

1.4

3

800

15

5

V

A

A

A

% mA

µA

µA mV/D mV/

(D - 0.5)

2 _______________________________________________________________________________________

Dual-Output (+ and -) DC-DC

Converters for CCD

ELECTRICAL CHARACTERISTICS (continued)

(V

CC

= V

AVCC

= V

ONINV =

V

ONBST

= 3.6V, PGND = SEQ = GND, C6 = 0.22µF, C1 = 2.2µF, C2 = 4.7µF, Figure 1, T

A

= 0°C to +85°C, unless otherwise noted. Typical values are at T

A

= +25°C.)

PARAMETER MIN MAX UNITS

FBP Load Regulation

FBN Load Regulation

Oscillator Frequency

Soft-Start Interval

Overload-Protection Fault Delay

FBP, FBN, REFERENCE

REF Output Voltage

REF Load Regulation

REF Line Regulation

FBP Threshold Voltage

FBN Threshold Voltage

FBP Input Leakage Current

FBN Input Leakage Current

LXN Input Leakage Current

LXP Input Leakage Current

PVP Input Leakage Current

FLT Input Leakage Current

CONDITIONS

I

LXP

= I

ILIMMIN

, MAX8614B

I

LXP

= I

ILIMMIN

, MAX8614A

I

LXN

= I

ILIMMIN

, MAX8614B

I

LXN

= I

ILIMMIN

, MAX8614A

Step-up and inverter

No load

0µA < I

REF

< 50µA

3.3V < V

AVCC

< 5.5V

No load

No load

V

FBP

=1.025V

T

A

= +25°C

T

A

= +85°C

T

A

= +25°C

FBN = -10mV

T

A

= +85°C

T

A

= +25°C

V

LXN

= -12V

T

A

= +85°C

T

A

= +25°C

V

LXP

= 23V

T

A

= +85°C

T

A

= +25°C

V

PVP

= 0V

T

A

= +85°C

T

A

= +25°C

V

FLT

= 3.6V

T

A

= +85°C

Fault mode, T

A

= +25°C

0.93

TYP

-15

-35

17.5

65

1

10

100

1.07

1.24

1.25

10

2

1.26

+0.1

10

5

0.995

1.010

1.025

-10 0 +10

-50 +5

+5

+50

-50 +50

-5

+5

+5

+0.1

+0.1

+5

-5

-5

-1

+0.1

+0.1

+0.1

+0.1

+0.1

+5

+5

+1

20 mV/A mV/A

MHz ms ms

V mV mV

V mV nA nA

µA

µA

µA

µA

Ω FLT Input Resistance

ONINV, ONBST, SEQ LOGIC INPUTS

Logic-Low Input

Logic-High Input

Bias Current

2.7V < V

AVCC

< 5.5V

2.7V < V

AVCC

< 5.5V

T

A

= +25°C

1.6

0.1

0.5

1

V

V

µA

_______________________________________________________________________________________ 3

Dual-Output (+ and -) DC-DC

Converters for CCD

ELECTRICAL CHARACTERISTICS

(V

CC

= V

AVCC

= V

ONINV =

V

ONBST

= V

EN

= 3.6V, PGND = SEQ = GND, C6 = 0.22µF, C1 = 2.2µF, C2 = 6.7µF, Figure 1, T

A

= -40°C

to +85°C, unless otherwise noted.) (Note 3)

PARAMETER

A

VCC

= V

CC

Voltage Range

UVLO Threshold

Step-Up Output Voltage Adjust Range

Inverter Output Voltage Adjust Range

(Note 1)

V

CC

rising

CONDITIONS MIN

3

2.42

V

AVCC

-16

0.7

0.34

0.9

0.52

0.65

0.28

TYP MAX

5.5

2.82

24

0

0.9

0.52

1.2

0.70

0.85

0.38

1.1

0.3

UNITS

V

V

V

V

LXP Current Limit

LXP Short-Circuit Current Limit

LXN Current Limit

LXN On-Resistance

PVP On-Resistance

Maximum Duty Cycle

V

INV

- V

CC

(Note 2)

MAX8614B

MAX8614A

MAX8614B

MAX8614A

MAX8614B

MAX8614A

V

CC

= 3.6V

V

CC

= 3.6V

Step-up and inverter

I

AVCC

I

VCC

I

AVCC

I

VCC

82

A

A

A

%

Quiescent Current (Switching, No Load)

Quiescent Current (No Switching, No Load)

Oscillator Frequency

FBP, FBN, REFERENCE

REF Output Voltage

FBP Threshold Voltage

FBN Threshold Voltage

ONINV, ONBST SEQ LOGIC INPUTS

Logic-Low Input

Logic-High Input

No load

No load

No load

2.7V < V

AVCC

< 5.5V

2.7V < V

AVCC

< 5.5V

0.93

1.235

0.995

-10

1.6

1.4

3

800

15

1.07

1.260

1.025

+10

0.5

mA

µA

MHz

V

V mV

V

V

Note 1: Output current and on-resistance are specified at 3.6V input voltage. The IC operates to 2.7V with reduced performance.

Note 2: The specified maximum negative output voltage is referred to V

CC

, and not to GND. With V

CC

= 3.3V, the maximum negative output is then -12.7V.

Note 3: Specifications to -40°C are guaranteed by design, not production tested.

4 _______________________________________________________________________________________

Dual-Output (+ and -) DC-DC

Converters for CCD

Typical Operating Characteristics

(T

A

= +25°C, V

CC

= V

AVCC

= 3.6V, SEQ = GND, Figure 1, unless otherwise noted.)

350

300

250

200

150

100

MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE

V

OUT

= 10V

V

OUT

= 15V

50

0

2.5

100

90

80

70

60

50

40

30

20

10

0

0.1

3.0

V

OUT

= 20V

3.5

4.0

4.5

INPUT VOLTAGE (V)

POSITIVE OUTPUT EFFICIENCY vs. OUTPUT CURRENT

V

CC

= 5V

V

CC

= 3V

5.0

V

CC

= 3.6V

V

CC

= 4.2V

5.5

L = 10

µH, C = 10µF

1 10

OUTPUT CURRENT (mA)

100

200

150

100

50

MAXIMUM OUTPUT CURRENT

300

250

V

INV

= -5V

vs. INPUT VOLTAGE

V

INV

= -7.5V

V

INV

= -10V

100

90

80

70

60

50

40

30

20

10

0

0.1

POSITIVE OUTPUT EFFICIENCY vs. OUTPUT CURRENT

V

CC

= 5V

V

CC

= 3V

V

CC

= 3.6V

V

CC

= 4.2V

L = 2.2

µH, C = 2.2µF

1 10

OUTPUT CURRENT (mA)

100

0

2.5

OUTPUT EFFICIENCY vs. OUTPUT CURRENT

100

90

80

70

V

CC

= 5V

60

50

V

CC

= 3V

V

CC

= 4.2V

V

CC

= 3.6V

40

30

20

10

0

0.1

BOTH OUTPUTS LOADED EQUALLY

L1 = 2.2

µH, C1 = 2.2µF, L2 = 4.7µH, C2 = 4.7µF

1 10

OUTPUT CURRENT (mA)

100

3.0

3.5

4.0

4.5

INPUT VOLTAGE (V)

5.0

5.5

100

90

80

70

60

50

40

30

20

10

0

0.1

NEGATIVE OUTPUT EFFICIENCY vs. OUTPUT CURRENT

V

CC

= 3V

V

CC

= 3.6V

V

CC

= 4.2V

V

CC

= 5V

L = 4.7

µH, C = 4.7µF

1 10

OUTPUT CURRENT (mA)

100

100

90

80

70

60

50

40

30

20

10

0

0.1

NEGATIVE OUTPUT EFFICIENCY vs. OUTPUT CURRENT

V

CC

= 3V

V

CC

= 3.6V

V

CC

= 4.2V

V

CC

= 5V

L = 10

µH, C = 10µF

1 10

OUTPUT CURRENT (mA)

100

OUTPUT EFFICIENCY vs. OUTPUT CURRENT

100

90

V

CC

= 5V

80

70

V

CC

= 4.2V

60

50

V

CC

= 3V

V

CC

= 3.6V

40

30

20

10

0

0.1

BOTH OUTPUTS LOADED EQUALLY

L1 = 10

µH, C1 = 10µF, L2 = 10µH, C2 = 10µF

1 10 100

OUTPUT CURRENT (mA)

1000

_______________________________________________________________________________________

5

Dual-Output (+ and -) DC-DC

Converters for CCD

Typical Operating Characteristics (continued)

(T

A

= +25°C, V

CC

= V

AVCC

= 3.6V, SEQ = GND, Figure 1, unless otherwise noted.)

1000

900

800

700

600

500

400

300

200

100

0

2.5

0

CHANGE IN OUTPUT VOLTAGE vs. LOAD CURRENT (POSITIVE OUTPUT)

-0.5

V

CC

= 5V

V

CC

= 4.2V

-1.0

-1.5

-2.0

-2.5

-3.0

V

CC

= 3V

V

CC

= 3.6V

-3.5

0 25 50 75 100

LOAD CURRENT (mA)

125 150

NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE

3.0

AV

CC

V

CC

3.5

4.0

4.5

INPUT VOLTAGE (V)

5.0

5.5

V

ONINV

V

ONBST

SOFT-START WAVEFORMS

MAX8614A/B toc13

SEQ = AV

CC

V

BST

V

INV

5V/div

0V

10V/div

0V

5V/div

I

IN

100mA/div

0V

4ms/div

V

ONINV

V

ONBST

V

BST

V

INV

SOFT-START WAVEFORMS

MAX8614A/B toc12

SEQ = GND

5V/div

0V

10V/div

0V

5V/div

I

IN

100mA/div

0V

4ms/div

V

BST

V

IN

3.5V TO 4.5V

TO 3.5V

-2.0

-2.5

-3.0

-3.5

0

0

CHANGE IN OUTPUT VOLTAGE vs. OUTPUT CURRENT (NEGATIVE OUTPUT)

V

OUT

- = -7.5V

-0.5

V

IN

= 5V

-1.0

V

IN

= 4.2V

-1.5

V

IN

= 3V

V

IN

= 3.6V

25 50 75

OUTPUT CURRENT (mA)

100 125

V

INV

LINE TRANSIENT

MAX8614A/B toc14

50mV/div

AC-COUPLED

40

µs/div

3.5V

50mV/div

AC-COUPLED

6 _______________________________________________________________________________________

Dual-Output (+ and -) DC-DC

Converters for CCD

Typical Operating Characteristics (continued)

(T

A

= +25°C, V

CC

= V

AVCC

= 3.6V, SEQ = GND, Figure 1, unless otherwise noted.)

V

INV

LOAD TRANSIENT (POSITIVE OUTPUT)

MAX8614A/B toc15

20mV/div

AC-COUPLED

V

BST

100mV/div

AC-COUPLED

I

BST

20mA TO 50mA

TO 20mA

4

µs/div

20mA/div

0V

SWITCHING WAVEFORMS (POSITIVE OUTPUT)

MAX8614A/B toc17

V

BST

V

LX

50mV/div

AC-COUPLED

10V/div

0V

I

LX

I

BST

= 20mA

400ns/div

500mA/div

0A

V

BST

V

INV

LOAD TRANSIENT (NEGATIVE OUTPUT)

MAX8614A/B toc16

50mV/div

AC-COUPLED

100mV/div

AC-COUPLED

I

INV

20mA TO 100mA

TO 20mA

4

µs/div

50mA/div

0V

SWITCHING WAVEFORMS (POSITIVE OUTPUT)

MAX8614A/B toc18

V

BST

V

LX

50mV/div

AC-COUPLED

10V/div

0V

I

LX

I

BST

= 50mA

400ns/div

500mA/div

0A

SWITCHING WAVEFORMS (NEGATIVE OUTPUT)

MAX8614A/B toc19

V

INV

V

LX

50mV/div

AC-COUPLED

10V/div

0V

SWITCHING WAVEFORMS (NEGATIVE OUTPUT)

MAX8614A/B toc20

V

INV

V

LX

50mV/div

AC-COUPLED

10V/div

0V

I

LX

I

INV

= 20mA

400ns/div

500mA/div

0A

I

LX

I

INV

= 100mA

400ns/div

500mA/div

0A

_______________________________________________________________________________________

7

Dual-Output (+ and -) DC-DC

Converters for CCD

Typical Operating Characteristics (continued)

(T

A

= +25°C, V

CC

= V

AVCC

= 3.6V, SEQ = GND, Figure 1, unless otherwise noted.)

2

3

4

5

6

7

PIN

1

8

9

10

11

12

REFERENCE VOLTAGE vs. TEMPERATURE

1.2490

1.2485

1.2480

1.2475

1.2470

1.2465

1.2460

1.2455

1.2450

-40 -15 10 35

TEMPERATURE (

°C)

60

V

CC

LXN

EP

connected to AV

CC

.

85

SWITCHING FREQUENCY vs. TEMPERATURE

1.006

1.005

1.004

1.003

1.002

1.001

1.000

0.999

0.998

0.997

0.996

-40

I

V

I

OUT

V

INV

BST

OUT

= -7.5V

= 100mA

= +15V

= 50mA

-15 10 35

TEMPERATURE (

°C)

60 85

Power Input Supply. VCC supplies power for the step-up and inverting DC-DC converters. V

CC

must be

Negative Output Switching Inductor Node. LXN is high impedance in shutdown.

Exposed Pad. Connect exposed paddle to ground.

Pin Description

NAME

ONBST

SEQ

FUNCTION

Enable Logic Input. Connect ONBST to AV

CC

for automatic startup of the step-up converter, or use ONBST as an independent control of the step-up converter.

FBN

FBP

Negative Output Feedback Input. Connect a resistor-divider between the negative output and REF with the center to FBN to set the negative output voltage.

AV

CC

Bias Supply. AV

CC

powers the IC. AV

CC

must be connected to V

CC

.

REF 1.25V Reference Voltage Output. Bypass with a 0.22µF ceramic capacitor to GND.

GND

FLT

Ground. Connect GND to PGND with a short trace.

Fault Open-Drain Output. Connect a 100k

Ω resistor from FLT to AV

CC

. FLT is active low during a fault event and is high impedance in shutdown.

Positive Output-Voltage Feedback Input. Connect a resistor-divider between the positive output and GND with the center to FBP to set the positive output voltage. FBP is high impedance in shutdown.

Sequence Logic Input. When SEQ = low, power-on sequence can be independently controlled by ONBST and ONINV. When SEQ = high, the positive output powers up before the negative output.

ONINV

Enable Logic Input. Connect ONINV to AV

CC

for automatic startup of the inverter, or use ONINV as an independent control of the inverter.

LXP Positive Output Switching Inductor Node. LXP is high impedance in shutdown.

PGND Power Ground. Connect PGND to GND with a short trace.

PVP

True-Shutdown Load Disconnect Switch. Connect one side of the inductor to PVP and the other side to LXP.

PVP is high impedance in shutdown.

13

14

8 _______________________________________________________________________________________

Dual-Output (+ and -) DC-DC

Converters for CCD

Functional Diagram

ERROR

AMPLIFIER

PWM

COMPARATOR

INVERTER

CURRENT SENSE

1.01V

REFERENCE

1.25V

INVERTER

CONTROL

LOGIC

MAX8614A

MAX8614B

V

CC

LXN

FBN

REF

ONBST

ONINV

FLT

SEQ

AV

CC

BIAS

AND

CONTROL

BLOCK

SOFT-START

1MHz

OSCILLATOR

ERROR

AMPLIFIER

PWM

COMPARATOR

STEP-UP

CONTROL

LOGIC

STEP-UP

CURRENT SENSE

PVP

LXP

PGND

FBP

GND

Detailed Description

The MAX8614A/MAX8614B generate both a positive and negative output voltage by combining a step-up and an inverting DC-DC converter on one IC. Both the step-up converter and the inverter share a common clock. Each output is independently regulated.

Each output is separately controlled by a pulse-widthmodulated (PWM) current-mode regulator. This allows the converters to operate at a fixed frequency (1MHz) for use in noise-sensitive applications. The 1MHz switching rate allows for small external components.

Both converters are internally compensated and are optimized for fast transient response (see the Load-

Transient Response/Voltage Positioning section).

Step-Up Converter

The step-up converter generates a positive output voltage up to 24V. An internal power switch, internal True-

Shutdown load switch (PVP), and external catch diode allow conversion efficiencies as high as 90%. The internal load switch disconnects the battery from the load by opening the battery connection to the inductor, providing True Shutdown. The internal load switch stays on at all times during normal operation. The load switch is used in the control scheme for the converter and cannot be bypassed.

_______________________________________________________________________________________ 9

Dual-Output (+ and -) DC-DC

Converters for CCD

Inverter

The inverter generates output voltages down to -16V below V

CC

. An internal power switch and external catch diode allow conversion efficiencies as high as 85%.

Control Scheme

Both converters use a fixed-frequency, PWM currentmode control-scheme. The heart of the current-mode

PWM controllers is a comparator that compares the error-amp voltage-feedback signal against the sum of the amplified current-sense signal and a slope-compensation ramp. At the beginning of each clock cycle, the internal power switch turns on until the PWM comparator trips. During this time the current in the inductor ramps up, storing energy in the inductor’s magnetic field. When the power switch turns off, the inductor releases the stored energy while the current ramps down, providing current to the output.

Fault Protection

The MAX8614A/MAX8614B have robust fault and overload protection. After power-up the device is set to detect an out-of-regulation state that could be caused by an overload or short condition at either output. If either output remains in overload for more than 100ms, both converters turn off and the FLT flag asserts low. During a short-circuit condition longer than 100ms on the positive output, foldback current limit protects the output. During a short-circuit condition longer than 100ms on the negative output, both converters turn off and the FLT flag asserts low. The converters then remain off until the device is reinitialized by resetting the controller.

The MAX8614A/MAX8614B also have thermal shutdown.

When the device temperature reaches +170°C (typ) the device shuts down. When it cools down by 20°C (typ), the converters turn on.

Enable (ONBST/ONINV)

Applying a high logic-level signal to ONBST/ONINV turns on the converters using the soft-start and poweron sequencing described below. Pulling ONBST/

ONINV low puts the IC in shutdown mode, turning off the internal circuitry. When ONBST/ONINV goes high

(or if power is applied with ONBST/ONINV high), the power-on sequence is set by SEQ. In shutdown, the device consumes only 0.1µA and both output loads are disconnected from the input supply.

Soft-Start and Inrush Current

The step-up converter and inverter in the MAX8614A/

MAX8614B feature soft-start to limit inrush current and minimize battery loading at startup. This is accomplished by ramping the reference voltage at the input of each error amplifier. The step-up reference is ramped from 0 to 1V (where 1V is the desired feedback voltage for the step-up converter) while the inverter reference is ramped down from 1.25V to 0 (where 0 is the desired feedback voltage for the inverter).

During startup, the step-up converter True-Shutdown load switch turns on before the step-up-converter reference voltage is ramped up. This effectively limits inrush current peaks to below 500mA during startup.

Undervoltage Lockout (UVLO)

The MAX8614A/MAX8614B feature undervoltage-lockout (UVLO) circuitry, which prevents circuit operation and MOSFET switching when AV

CC is less than the

UVLO threshold (2.55V, typ). The UVLO comparator has 25mV of hysteresis to eliminate chatter due to the source supply output impedance.

Power-On Sequencing (SEQ)

The MAX8614A/MAX8614B have pin-selectable internally programmed power-on sequencing. This sequencing covers all typical sequencing options required by CCD imagers.

When SEQ = 0, power-on sequence can be independently controlled by ONINV and ONBST. When SEQ =

0 and ONINV and ONBST are pulled high, both outputs reach regulation simultaneously. The inverter is held off while the step-up True-Shutdown switch slowly turns on to pull PVP to V

CC

. The positive output rises to a diode drop below V

CC

. Once the step-up output reaches this voltage, the step-up and the inverter then ramp their respective references over a period of 7ms. This brings the two outputs into regulation at approximately the same time.

When SEQ = 1 and ONBST and ONINV are pulled high, the step-up output powers on first. The inverter is held off until the step-up completes its entire soft-start cycle and the positive output is in regulation. Then the inverter starts its soft-start cycle and achieves regulation in about 7ms.

True Shutdown

The MAX8614A/MAX8614B completely disconnect the loads from the input when in shutdown mode. In most step-up converters the external rectifying diode and inductor form a DC current path from the battery to the output. This can drain the battery even in shutdown if a load is connected at the step-up converter output. The

MAX8614A/MAX8614B have an internal switch between the input V

CC and the inductor node, PVP. When this switch turns off in shutdown there is no DC path from the input to the output of the step-up converter. This load disconnect is referred to as “True Shutdown.” At

10 ______________________________________________________________________________________

Dual-Output (+ and -) DC-DC

Converters for CCD

the inverter output, load disconnect is implemented by turning off the inverter’s internal power switch.

Current-Limit Select

The MAX8614B allows an inductor current limit of 0.8A

on the step-up converter and 0.75A on the inverter. The

MAX8614A allows an inductor current limit of 0.44A on the step-up converter and 0.33A on the inverter. This allows flexibility in designing for higher load-current applications or for smaller, more compact designs when less power is needed. Note that the currents listed above are peak inductor currents and not output currents. The MAX8614B output current is 50mA at +15V and 100mA at -7.5V. The MAX8614A output current is

25mA at +15V and 50mA at -7.5V.

Load Transient/Voltage Positioning

The MAX8614A/MAX8614B match the load regulation to the voltage droop seen during load transients. This is sometimes called voltage positioning. This results in minimal overshoot when a load is removed and minimal voltage drop during a transition from light load to full load.

The use of voltage positioning allows superior load-transient response by minimizing the amplitude of overshoot and undershoot in response to load transients. DC-DC converters with high control-loop gains maintain tight

DC load regulation but still allow large voltage drops of

5% or greater for several hundred microseconds during transients. Load-transient variations are seen only with an oscilloscope (see the Typical Operating

Characteristics). Since DC load regulation is read with a voltmeter, it does not show how the power supply reacts to load transients.

Applications Information

Adjustable Output Voltage

The positive output voltage is set by connecting FBP to a resistive voltage-divider between the output and GND

(Figure 1). Select feedback resistor R2 in the 30k

Ω to

100k

Ω range. R1 is then given by:

R 1

=

R 2



V

BST

V

FBP

1

 where V

FBP

= 1.01V.

The negative output voltage is set by connecting FBN to a resistive voltage-divider between the output and

REF (Figure 1). Select feedback resistor R4 in the 30k

Ω to 100k

Ω range. R3 is then given by:

R 3

=

R 4

×



V

FBN

V

IMV

V

REF

V

FBN

 where V

REF

= 1.25V and V

FBN

= 0V.

Inductor Selection

The MAX8614A/MAX8614B high switching frequency allows for the use of a small inductor. The 4.7µH and

2.2µH inductors shown in the Typical Operating Circuit is recommended for most applications. Larger inductances reduce the peak inductor current, but may result in skipping pulses at light loads. Smaller inductances require less board space, but may cause greater peak current due to current-sense comparator propagation delay.

Use inductors with a ferrite core or equivalent. Powder iron cores are not recommended for use with high switching frequencies. The inductor’s incremental saturation rating must exceed the selected current limit. For highest efficiency, use inductors with a low DC resistance

(under 200m

Ω); however, for smallest circuit size, higher resistance is acceptable. See Table 1 for a representative list of inductors and Table 2 for component suppliers.

Diode Selection

The MAX8614A/MAX8614B high switching frequency demands a high-speed rectifier. Schottky diodes, such as the CMHSH5-2L or MBR0530L, are recommended.

Make sure that the diode’s peak current rating exceeds the selected current limit, and that its breakdown voltage exceeds the output voltage. Schottky diodes are preferred due to their low forward voltage. However, ultrahigh-speed silicon rectifiers are also acceptable.

Table 2 lists component suppliers.

Capacitor Selection

Output Filter Capacitor

The primary criterion for selecting the output filter capacitor is low effective series resistance (ESR). The product of the peak inductor current and the output filter capacitor’s ESR determines the amplitude of the high-frequency ripple seen on the output voltage.

These requirements can be balanced by appropriate selection of the current limit.

For stability, the positive output filter capacitor, C1, should satisfy the following:

C1 > (6L I

BSTMAX

) / ( R

CS

D+ V

BST

2

) where R

CS

= 0.015 (MAX8614B), and 0.035 (MAX8614A).

D+ is 1 minus the step-up switch duty cycle and is:

D+ = V

CC

/ V

BST

______________________________________________________________________________________ 11

Dual-Output (+ and -) DC-DC

Converters for CCD

Table 1. Inductor Selection Guide

OUTPUT VOLTAGES

AND LOAD CURRENT

INDUCTOR

15V, 50mA

-7.5V, 100mA

15V, 20mA

-7.5V, 40mA

TOKO

DB3018C, 1069AS-2R0

TOKO

DB3018C, 1069AS-4R3

TOKO

S1024AS-4R3M

Sumida

CDRH2D14-4R7

TOKO

S1024AS-100M

Sumida

CDRH2D11-100

Sumida

CDRH2D14-100

Murata

LQH32CN100K33

L (

µH)

2.0

4.3

4.3

4.7

10

10

10

10

DCR (m

)

72

126

47

170

100

400

295

300

I

SAT

(A)

1.4

0.97

1.2

1

0.8

0.35

0.46

0.45

SIZE (mm)

3 x 3 x 1.8

3 x 3 x 1.8

4 x 4 x 1.7

3.2 x 3.2 x 1.55

4 x 4 x 1.7

3.2 x 3.2 x 1.2

3.2 x 3.2 x 1.55

3.2 x 2.5 x 2

Table 2. Component Suppliers

SUPPLIER

INDUCTORS

Murata

Sumida

TOKO

DIODES

Central

Semiconductor

(CMHSH5-2L)

Motorola

(MBR0540L)

CAPACITORS

Taiyo Yuden

TDK

PHONE WEBSITE

770-436-1300 www.murata.com

847-545-600 www.sumida.com

847-297-0070 www.tokoam.com

631-435-1110 www.centralsemi.com

602-303-5454 www.motorola.com

408-573-4150 www.t-yuden.com

888-835-6646 www.TDK.com

For stability, the inverter output filter capacitor, C2, should satisfy the following:

C2 > (6L V

REF

I

INVMAX

) /

(R

CS

D- (V

REF

- V

INV

) V

INV

) where R

CS

= 0.0175 (MAX8614B), and 0.040

(MAX8614A). D- is 1 minus the inverter switch duty cycle and is:

D- = V

CC

/ V

INV

Table 2 lists representative low-ESR capacitor suppliers.

Input Bypass Capacitor

Although the output current of many MAX8614A/

MAX8614B applications may be relatively small, the input must be designed to withstand current transients equal to the inductor current limit. The input bypass capacitor reduces the peak currents drawn from the voltage source, and reduces noise caused by the

MAX8614A/MAX8614B switching action. The input source impedance determines the size of the capacitor required at the input. As with the output filter capacitor, a low-ESR capacitor is recommended. A 22µF, low-ESR capacitor is adequate for most applications, although smaller bypass capacitors may also be acceptable with low-impedance sources or if the source supply is already well filtered. Bypass AV

CC separately from V

CC with a 1.0µF ceramic capacitor placed as close as possible to the AV

CC and GND pins.

PCB Layout and Routing

Proper PCB layout is essential due to high-current levels and fast-switching waveforms that radiate noise.

Breadboards or protoboards should never be used when prototyping switching regulators.

12 ______________________________________________________________________________________

Dual-Output (+ and -) DC-DC

Converters for CCD

V

BATT

(2.7V ~ 5V)

FAULT

R5

100k

C4

22

µF

R3

187k

1%

V

INV

1

9

2

13

V

CC

ONBST

ONINV

FBN

V

BATT

C5

1.0

µF

R4

30.9k

1%

C6

0.22

µF

REF

3

4

AV

CC

REF

MAX8614A

MAX8614B

LXN

14

PVP

12

L2

4.7

µH

L1

2.2

µH

6

FLT

LXP

10

V

BST

D2

CMHSH5-21

V

INV

C2

-7.5V AT 100mA

4.7

µF

C3

1

µF

D1

CMHSH5-21

V

BST

C1

+15V AT 50mA

2.2

µF

R1

1.4M

1%

R2

100k

1%

7

FBP

GND

5

PGND

11

SEQ

8

Figure 1. Typical Application Circuit

It is important to connect the GND pin, the input bypass-capacitor ground lead, and the output filter capacitor ground lead to a single point (star ground configuration) to minimize ground noise and improve regulation. Also, minimize lead lengths to reduce stray capacitance, trace resistance, and radiated noise, with preference given to the feedback circuit, the ground circuit, and LX_. Place feedback resistors R1–R4 as close to their respective feedback pins as possible.

Place the input bypass capacitor as close as possible to AV

CC and GND.

Chip Information

PROCESS: BiCMOS

______________________________________________________________________________________ 13

Dual-Output (+ and -) DC-DC

Converters for CCD

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)

14 ______________________________________________________________________________________

Dual-Output (+ and -) DC-DC

Converters for CCD

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)

COMMON DIMENSIONS

SYMBOL MIN.

MAX.

A

D

E

A1

L k

0.70

2.90

2.90

0.00

0.20

0.80

3.10

3.10

0.05

0.40

0.25 MIN.

A2 0.20 REF.

PACKAGE VARIATIONS

PKG. CODE

T633-2

T833-2

T833-3

T1033-1

T1033-2

T1433-1

T1433-2

N

6

8

8

10

10

14

14

D2

1.50–0.10

1.50–0.10

1.50–0.10

1.50–0.10

1.50–0.10

1.70–0.10

1.70–0.10

E2

2.30–0.10

2.30–0.10

2.30–0.10

2.30–0.10

2.30–0.10

2.30–0.10

2.30–0.10

e

0.95 BSC

0.65 BSC

0.65 BSC

0.50 BSC

0.50 BSC

0.40 BSC

0.40 BSC

JEDEC SPEC

MO229 / WEEA

MO229 / WEEC

MO229 / WEEC

MO229 / WEED-3

MO229 / WEED-3

- - - -

- - - - b

0.40–0.05

0.30–0.05

0.30–0.05

0.25–0.05

0.25–0.05

0.20–0.05

0.20–0.05

[(N/2)-1] x e

1.90 REF

1.95 REF

1.95 REF

2.00 REF

2.00 REF

2.40 REF

2.40 REF

Revision History

Pages changed at Rev 1: 1, 12, 14, 15

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 15

© 2006 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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