Rainbow Electronics MAX8614B User Manual

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

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

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC

Converters for CCD

________________________________________________________________ Maxim Integrated Products 1

19-4014; Rev 0; 3/06

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.

14 13 12 11 10

9

8

1

+

23

4567

LXN

VCCPVP

PGNDREF

AV

CC

FBN

ONBST

TOP VIEW

MAX8614A
MAX8614B

LXP

ONINV

SEQFBP

FLT

GND

TDFN

Pin Configuration

Typical Operating Circuit

Ordering Information

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

+Denotes lead-free package.

PART

MAX8614AETD+

MAX8614BETD+

INPUT

(2.7V TO 5.5V)

TEMP

RANGE

-40°C to
+85°C

-40°C to
+85°C

PIN­PACKAGE

14 TDFN
3mm x 3mm
(T1433-2)

14 TDFN
3mm x 3mm
(T1433-2)

TOP

MARK

ABG 0.44/0.33

ABH 0.8/0.75

ILIM

BST/INV

V

CC

ONINV

ONBST

AV

CC

MAX8614A
MAX8614B

REF

AV

CC

SEQ

FLT

GND PGND

LXN

FBN
PVP

LXP

FBP

V

-7.5V

V
+15V

INV

REF

BST

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC
Converters for CCD

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.

VCC, AVCCto 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 VCC..........................................................-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

ELECTRICAL CHARACTERISTICS

(VCC= V

AVCC

= V

ONINV = VONBST

= 3.6V, PGND = SEQ = GND, C6 = 0.22µF, C1 = 2.2µF, C2 = 4.7µF, Figure 1, TA= 0°C to +85°C,

unless otherwise noted. Typical values are at T

A

= +25°C.)

AVCC and VCC Voltage Range (Note 1) 2.7 5.5 V

UVLO Threshold VCC rising 2.42 2.55 2.66 V

UVLO Hysteresis 25 mV

Step-Up Output Voltage Adjust Range V

PARAMETER CONDITIONS MIN TYP MAX UNITS

AVCC

24 V

Inverter Output Voltage Adjust Range V

LXP Current Limit

LXP Short-Circuit Current Limit

LXN Current Limit

LXN On-Resistance V

LXP On-Resistance V

PVP On-Resistance V

Maximum Duty Cycle Step-up and inverter 82 90 %

Quiescent Current (Switching, No Load)

Quiescent Current (No Switching, No Load)

Shutdown Supply Current

FBP Line Regulation V

FBN Line Regulation V

- VCC (Note 2) -16 0 V

INV

MAX8614B 0.7 0.8 0.9

MAX8614A 0.34 0.44 0.52

MAX8614B 0.90 1.05 1.20

MAX8614A 0.52 0.61 0.70

MAX8614B 0.65 0.75 0.85

MAX8614A 0.28 0.33 0.38

= 3.6V 0.6 1.1 Ω

CC

= 3.6V 0.625 Ω

CC

= 3.6V 0.15 0.3 Ω

CC

I

AVCC

I

VCC

I

AVCC

I

V

CC

T

= +25°C 0.1 5

A

T

= +85°C 0.1

A

= 2.7V to 5.5V -20 mV/D

CC

= 2.7V to 5.5V 20

CC

0.75 1.4

23

400 800

815

mA

µA

µA

mV/

(D - 0.5)

A

A

A

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC

Converters for CCD

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VCC= V

AVCC

= V

ONINV = VONBST

= 3.6V, PGND = SEQ = GND, C6 = 0.22µF, C1 = 2.2µF, C2 = 4.7µF, Figure 1, TA= 0°C to +85°C,

unless otherwise noted. Typical values are at T

A

= +25°C.)

FBP Load Regulation

FBN Load Regulation

Oscillator Frequency 0.93 1 1.07 MHz

Soft-Start Interval Step-up and inverter 10 ms

Overload-Protection Fault Delay 100 ms

FBP, FBN, REFERENCE

REF Output Voltage No load 1.24 1.25 1.26 V

REF Load Regulation 0µA < I

REF Line Regulation 3.3V < V

FBP Threshold Voltage No load 0.995 1.010 1.025 V

FBN Threshold Voltage No load -10 0 +10 mV

FBP Input Leakage Current V

FBN Input Leakage Current FBN = -10mV

LXN Input Leakage Current V

LXP Input Leakage Current V

PVP Input Leakage Current V

FLT Input Leakage Current V

FLT Input Resistance Fault mode, T

ONINV, ONBST, SEQ LOGIC INPUTS

Logic-Low Input 2.7V < V

Logic-High Input 2.7V < V

Bias Current T

PARAMETER CONDITIONS MIN TYP MAX UNITS

I

= I

LXP

I

= I

LXP

I

= I

LXN

I

= I

LXN

FBP =

= -12V

LXN

= 23V

LXP

= 0V

PVP

= 3.6V

FLT

= +25°C 0.1 1 µA

A

, MAX8614B -15

ILIMMIN

, MAX8614A -35

ILIMMIN

, MAX8614B 17.5

ILIMMIN

, MAX8614A 65

ILIMMIN

< 50µA 10 mV

REF

< 5.5V 2 5 mV

AVCC

T

= +25°C -50 +5 +50

1.025V

= +25°C 10 20 Ω

A

< 5.5V 0.5 V

AVCC

< 5.5V 1.6 V

AVCC

A

T

= +85°C +5

A

T

= +25°C -50 +5 +50

A

T

= +85°C +5

A

T

= +25°C -5 +0.1 +5

A

T

= +85°C +0.1

A

T

= +25°C -5 +0.1 +5

A

T

= +85°C +0.1

A

T

= +25°C -5 +0.1 +5

A

T

= +85°C +0.1

A

T

= +25°C -1 +0.1 +1

A

T

= +85°C +0.1

A

mV/A

mV/A

nA

nA

µA

µA

µA

µA

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC
Converters for CCD

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS

(VCC= V

AVCC

= V

ONINV = VONBST

= VEN= 3.6V, PGND = SEQ = GND, C6 = 0.22µF, C1 = 2.2µF, C2 = 6.7µF, Figure 1, TA= -40°C

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

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 VCC= 3.3V, the maximum negative

output is then -12.7V.

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

A

= VCC Voltage Range (Note 1) 3 5.5 V

VCC

UVLO Threshold VCC rising 2.42 2.82 V

Step-Up Output Voltage Adjust Range V

Inverter Output Voltage Adjust Range V

LXP Current Limit

LXP Short-Circuit Current Limit

LXN Current Limit

LXN On-Resistance V

PVP On-Resistance V

Maximum Duty Cycle Step-up and inverter 82 %

Quiescent Current (Switching, No Load)

Quiescent Current (No Switching, No Load)

Oscillator Frequency 0.93 1.07 MHz

FBP, FBN, REFERENCE

REF Output Voltage No load 1.235 1.260 V

FBP Threshold Voltage No load 0.995 1.025 V

FBN Threshold Voltage No load -10 +10 mV

ONINV, ONBST SEQ LOGIC INPUTS

Logic-Low Input 2.7V < V

Logic-High Input 2.7V < V

PARAMETER CONDITIONS MIN TYP MAX UNITS

AVCC

- VCC (Note 2) -16 0 V

INV

MAX8614B 0.7 0.9

MAX8614A 0.34 0.52

MAX8614B 0.9 1.2

MAX8614A 0.52 0.70

MAX8614B 0.65 0.85

MAX8614A 0.28 0.38

= 3.6V 1.1 Ω

CC

= 3.6V 0.3 Ω

CC

I

AVCC

I

VCC

I

AVCC

I

VCC

< 5.5V 0.5 V

AVCC

< 5.5V 1.6 V

AVCC

24 V

1.4

3

800

15

A

A

A

mA

µA

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC

Converters for CCD

_______________________________________________________________________________________ 5

Typical Operating Characteristics

(TA= +25°C, VCC= V

AVCC

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

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE

350

300

250

200

150

100

MAXIMUM OUTPUT CURRENT (mA)

50

0

2.5 3.0 3.5 4.0 4.5 5.0 5.5

V

V

= 15V

OUT

INPUT VOLTAGE (V)

= 10V

OUT

V

= 20V

OUT

POSITIVE OUTPUT EFFICIENCY

vs. OUTPUT CURRENT

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 1 10 100

VCC = 5V

VCC = 3V

OUTPUT CURRENT (mA)

MAXIMUM OUTPUT CURRENT

vs. INPUT VOLTAGE

V

= -5V

INV

V

= -7.5V

INV

V

INPUT VOLTAGE (V)

NEGATIVE OUTPUT EFFICIENCY

vs. OUTPUT CURRENT

VCC = 3.6V

VCC = 3V

VCC = 5V

L = 4.7µH, C = 4.7µF

OUTPUT CURRENT (mA)

VCC = 3.6V

VCC = 4.2V

L = 10µH, C = 10µF

300

250

MAX8614A/B toc01

200

150

100

50

MAXIMUM OUTPUT CURRENT (mA) .

0

2.5 3.0 3.5 4.0 4.5 5.0 5.5

100

90

80

MAX8614A/B toc04

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 1 10 100

= -10V

INV

VCC = 4.2V

MAX8614A/B toc02

EFFICIENCY (%)

MAX8614A/B toc05

EFFICIENCY (%)

POSITIVE OUTPUT EFFICIENCY

vs. OUTPUT CURRENT

100

90

80

70

60

50

40

30

20

10

0

0.1 1 10 100
OUTPUT CURRENT (mA)

VCC = 5V

VCC = 3V

VCC = 3.6V

L = 2.2µH, C = 2.2µF

VCC = 4.2V

NEGATIVE OUTPUT EFFICIENCY

vs. OUTPUT CURRENT

100

90

80

70

60

50

40

30

20

10

0

0.1 1 10 100

VCC = 3.6V

VCC = 3V

VCC = 4.2V

VCC = 5V

L = 10µH, C = 10µF

OUTPUT CURRENT (mA)

MAX8614A/B toc03

MAX8614A/B toc06

OUTPUT EFFICIENCY

vs. OUTPUT CURRENT

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

BOTH OUTPUTS LOADED EQUALLY

10

L1 = 2.2µH, C1 = 2.2µF, L2 = 4.7µH, C2 = 4.7µF

0

0.1 1 10 100
OUTPUT CURRENT (mA)

VCC = 5V

VCC = 3V

VCC = 3.6V

VCC = 4.2V

MAX8614A/B toc07

100

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

0.1 1 10 100 1000

OUTPUT EFFICIENCY

vs. OUTPUT CURRENT

VCC = 5V

VCC = 4.2V

VCC = 3V

VCC = 3.6V

BOTH OUTPUTS LOADED EQUALLY
L1 = 10µH, C1 = 10µF, L2 = 10µH, C2 = 10µF

OUTPUT CURRENT (mA)

MAX8614A/B toc08

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC
Converters for CCD

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(TA= +25°C, VCC= V

AVCC

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

CHANGE IN OUTPUT VOLTAGE

vs. LOAD CURRENT (POSITIVE OUTPUT)

LOAD CURRENT (mA)

CHANGE IN OUTPUT VOLTAGE (%)

MAX8614A/B toc09

0 25 50 75 100 125 150

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0

VCC = 3V

VCC = 5V

VCC = 4.2V

VCC = 3.6V

CHANGE IN OUTPUT VOLTAGE

vs. OUTPUT CURRENT (NEGATIVE OUTPUT)

0

-0.5

-1.0

-1.5

-2.0

V

OUT

VIN = 4.2V

- = -7.5V

VIN = 5V

MAX8614A/B toc10

NO-LOAD SUPPLY CURRENT

1000

900

800

700

600

500

400

300

SUPPLY CURRENT (µA)

200

100

0

2.5 3.0 3.5 4.0 4.5 5.0 5.5

V

ONINV

V

ONBST

V

BST

V

INV

I

IN

vs. INPUT VOLTAGE

AV

CC

INPUT VOLTAGE (V)

SOFT-START WAVEFORMS

SEQ = AV

CC

4ms/div

V

CC

MAX8614A/B toc13

MAX8614A/B toc11

5V/div
0V

10V/div

0V

5V/div

100mA/div
0V

-2.5

CHANGE IN OUTPUT VOLTAGE (%)

-3.0

-3.5

VIN = 3V

0 25 50 75 100 125

SOFT-START WAVEFORMS

SEQ = GND

V

ONINV

V

ONBST

V

BST

V

INV

I

IN

V

BST

V

IN

3.5V TO 4.5V
TO 3.5V

V

INV

VIN = 3.6V

OUTPUT CURRENT (mA)

4ms/div

LINE TRANSIENT

40µs/div

MAX8614A/B toc12

MAX8614A/B toc14

5V/div
0V

10V/div

0V

5V/div

100mA/div
0V

50mV/div
AC-COUPLED

3.5V

50mV/div
AC-COUPLED

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC

Converters for CCD

_______________________________________________________________________________________ 7

Typical Operating Characteristics (continued)

(TA= +25°C, VCC= V

AVCC

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

LOAD TRANSIENT (POSITIVE OUTPUT)

V

INV

V

BST

I

BST

20mA TO 50mA
TO 20mA

4µs/div

SWITCHING WAVEFORMS (POSITIVE OUTPUT)

V

BST

V

LX

I

LX

I

= 20mA

BST

400ns/div

MAX8614A/B toc15

MAX8614A/B toc17

20mV/div
AC-COUPLED

100mV/div
AC-COUPLED

20mA/div

0V

50mV/div
AC-COUPLED

10V/div

0V

500mA/div
0A

LOAD TRANSIENT (NEGATIVE OUTPUT)

V

BST

V

INV

I

INV

20mA TO 100mA
TO 20mA

4µs/div

SWITCHING WAVEFORMS (POSITIVE OUTPUT)

V

BST

V

LX

I

LX

I

= 50mA

BST

400ns/div

MAX8614A/B toc16

MAX8614A/B toc18

50mV/div
AC-COUPLED

100mV/div
AC-COUPLED

50mA/div

0V

50mV/div
AC-COUPLED

10V/div

0V

500mA/div

0A

SWITCHING WAVEFORMS (NEGATIVE OUTPUT)

V

INV

V

LX

I

LX

I

= 20mA

INV

400ns/div

MAX8614A/B toc19

50mV/div
AC-COUPLED

10V/div

0V

500mA/div
0A

SWITCHING WAVEFORMS (NEGATIVE OUTPUT)

V

INV

V

LX

I

LX

I

= 100mA

INV

400ns/div

MAX8614A/B toc20

50mV/div
AC-COUPLED

10V/div

0V

500mA/div
0A

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC
Converters for CCD

8 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(TA= +25°C, VCC= V

AVCC

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

REFERENCE VOLTAGE

vs. TEMPERATURE

TEMPERATURE (°C)

REFERENCE VOLTAGE (V)

MAX8614A/B toc21

-40 -15 10 35 60 85

1.2450

1.2455

1.2460

1.2465

1.2470

1.2475

1.2480

1.2485

1.2490

SWITCHING FREQUENCY

vs. TEMPERATURE

TEMPERATURE (°C)

FREQUENCY (kHz)

MAX8614A/B toc22

-40 -15 10 35 60 85

0.996

0.997

0.998

0.999

1.000

1.001

1.002

1.003

1.004

1.005

1.006

V

BST

= +15V

I

OUT

= 50mA

V

INV

= -7.5V

I

OUT

= 100mA

PIN

FUNCTION

1

Enable Logic Input. Connect ONBST to AVCC for automatic startup of the step-up converter, or use ONBST
as an independent control of the step-up converter.

2 FBN

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.

3

Bias Supply. AVCC powers the IC. AVCC must be connected to VCC.

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

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

6 FLT

Fault Open-Drain Output. Connect a 100kΩ resistor from FLT to AV

CC

. FLT is active low during a fault event

and is high impedance in shutdown.

7 FBP

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.

8 SEQ

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.

9

Enable Logic Input. Connect ONINV to AVCC for automatic startup of the inverter, or use ONINV as an
independent control of the inverter.

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

11

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

12 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 V

CC

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

connected to AV

CC

.

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

— EP Exposed Pad. Connect exposed paddle to ground.

Pin Description

NAME

ONBST

AV

CC

ONINV

PGND

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC

Converters for CCD

_______________________________________________________________________________________ 9

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 True­Shutdown 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.

Functional Diagram

ONBST

ONINV

FLT

SEQ

AV

ERROR

AMPLIFIER

CURRENT SENSE

REFERENCE

1.01V

BIAS

AND

CONTROL

BLOCK

CC

SOFT-START

OSCILLATOR

1MHz

ERROR

AMPLIFIER

1.25V

CURRENT SENSE

COMPARATOR

INVERTER

COMPARATOR

STEP-UP

PWM

PWM

INVERTER
CONTROL

CONTROL

LOGIC

STEP-UP

LOGIC

MAX8614A
MAX8614B

V

CC

LXN

FBN

REF

PVP

LXP

PGND

FBP

GND

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC
Converters for CCD

10 ______________________________________________________________________________________

Inverter

The inverter generates output voltages down to -16V
below VCC. 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 VCC. The positive output rises to a diode
drop below VCC. 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 VCCand 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

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC

Converters for CCD

______________________________________________________________________________________ 11

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 load­transient 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 30kΩ to
100kΩ range. R1 is then given by:

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 30kΩ
to 100kΩ range. R3 is then given by:

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
200mΩ); 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

) / ( RCSD+ 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+ = VCC/ V

BST

R

VV
VV

FBN IMV

REF FBN

34=×

−

−

⎛
⎝

⎜

⎞
⎠

⎟

R

R

V
V

BST

FBP

12 1=−

⎛
⎝

⎜

⎞
⎠

⎟

R

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC
Converters for CCD

12 ______________________________________________________________________________________

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

C2 > (6L V

REFIINVMAX

) /

(RCSD- (V

REF

- V

INV

) V

INV

)

where RCS= 0.0175 (MAX8614B), and 0.040
(MAX8614A). D- is 1 minus the inverter switch duty cycle
and is:

D- = VCC/ 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 4.7µF, low­ESR 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 AVCCseparately
from VCCwith a 0.1µF ceramic capacitor placed as
close as possible to the AVCCand GND pins.

PC Board Layout and Routing

Proper PC board 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.

Table 1. Inductor Selection Guide

Table 2. Component Suppliers

OUTPUT VOLTAGES

AND LOAD CURRENT

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

INDUCTOR L (µH) DCR (mΩ)I

(A) SIZE (mm)

SAT

2.0 72 1.4 3 x 3 x 1.8

4.3 126 0.97 3 x 3 x 1.8

4.3 47 1.2 4 x 4 x 1.7

4.7 170 1 3.2 x 3.2 x 1.55

10 100 0.8 4 x 4 x 1.7

10 400 0.35 3.2 x 3.2 x 1.2

10 295 0.46 3.2 x 3.2 x 1.55

10 300 0.45 3.2 x 2.5 x 2

SUPPLIER PHONE WEBSITE

INDUCTORS

Murata 770-436-1300 www.murata.com

Sumida 847-545-600 www.sumida.com

TOKO 847-297-0070 www.tokoam.com

DIODES

Central
Semiconductor
(CMHSH5-2L)

Motorola
(MBR0540L)

CAPACITORS

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

TDK 888-835-6646 www.TDK.com

631-435-1110 www.centralsemi.com

602-303-5454 www.motorola.com

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC

Converters for CCD

______________________________________________________________________________________ 13

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 AVCCand GND.

Chip Information

PROCESS: BiCMOS

Figure 1. Typical Application Circuit

V

BATT

(2.7V ~ 5V)

FAULT

100kΩ

C4

MAX8614A
MAX8614B

4.7µF

LXN

PVP

LXP

SEQ

D2

4.7µH

2.2µH

L2

L1

CMHSH5-21

D1

CMHSH5-21

V

INV

-7.5V AT 100mA

C2

4.7µF

C3
1µF

V

BST

+15V AT 50mA

C1

2.2µF

14

12

10

8

V

INV

R3

187kΩ

1%

R4

30.9kΩ

1%

C5

0.1µF

V

BATT

R5

1.4MΩ

1%

100kΩ

1%

0.22µF

V

R1

R2

C6

BST

REF

1
9

2

3

4

6

7

ONBST
ONINV

FBN

AV

REF

FLT

13

V

CC

CC

FBP

GND PGND

511

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC
Converters for CCD

14 ______________________________________________________________________________________

MAX8614A/MAX8614B

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

.)

D

PIN 1
INDEX
AREA

E

A1

A

A2

DETAIL A

D2

PIN 1 ID

N

0.35x0.35

b

[(N/2)-1] x e

E2

k

C

L

L

e

e

REF.

e

C

L

L

6, 8, &10L, DFN THIN.EPS

PACKAGE OUTLINE, 6,8,10 & 14L,
TDFN, EXPOSED PAD, 3x3x0.80 mm

-DRAWING NOT TO SCALE-

21-0137

1

G

2

MAX8614A/MAX8614B

Dual-Output (+ and -) DC-DC

Converters for CCD

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 Printed USA is a registered trademark of Maxim Integrated Products, Inc.

MAX8614A/MAX8614B

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

A

D

E 2.90 3.10

A1

L 0.20 0.40

A2 0.20 REF.

MIN. MAX.

0.70 0.80

2.90 3.10

0.00 0.05

0.25 MIN.k

PACKAGE VARIATIONS

PKG. CODE

T633-2 6 1.50±0.10 2.30±0.10 0.95 BSC

T833-2 8 1.50±0.10 2.30±0.10

T833-3 8 1.50±0.10 2.30±0.10

-DRAWING NOT TO SCALE-

N

D2 E2 e

2.30±0.101.50±0.106T633-1 0.95 BSC MO229 / WEEA 1.90 REF0.40±0.05

1.50±0.10

1.50±0.10

1.70±0.10 2.30±0.1014T1433-1

2.30±0.108T833-1

2.30±0.1010T1033-1

JEDEC SPEC

MO229 / WEEA

0.65 BSC

0.65 BSC MO229 / WEEC

0.65 BSC MO229 / WEEC

0.50 BSC

0.40 BSC

0.40 BSC

MO229 / WEEC

MO229 / WEED-3

- - - - 0.20±0.05 2.40 REFT1433-2 14 2.30±0.101.70±0.10

b

[(N/2)-1] x e

0.40±0.05 1.90 REF

1.95 REF0.30±0.05

0.30±0.05 1.95 REF

0.30±0.05 1.95 REF

2.00 REF0.25±0.05

2.40 REF0.20±0.05- - - -

DOWNBONDS

ALLOWED

NO

NO

NO

NO

YES

NO

YES

NO

PACKAGE OUTLINE, 6,8,10 & 14L,
TDFN, EXPOSED PAD, 3x3x0.80 mm

21-0137

2

G

2