19-4014; Rev 2; 6/14
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
EVALUATION KIT AVAILABLE
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
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 applica-
tions 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 space-
saving 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
oDual Output Voltages (+ and -)
oAdjustable Up to +24V and Down to -10V at 5.5VIN
oOutput Short/Overload Protection
oTrue Shutdown on Both Outputs
oControlled Inrush Current During Soft-Start
oSelectable Power-On Sequencing
oUp to 90% Efficiency
o1µA Shutdown Current
o1MHz Fixed-Frequency PWM Operation
oFault-Condition Flag
oThermal Shutdown
oSmall, 3mm x 3mm, 14-Pin TDFN Package
14 13 12 11 10 98
1
+
234567
LXN
VCC
PVP
PGNDREF
AVCC
FBN
ONBST
TOP VIEW
MAX8614A
MAX8614B
LXP
ONINV
SEQFBP
FLT
GND
TDFN
Pin Configuration
LXN
VCC
INPUT
(2.7V TO 5.5V)
REF
AVCC
AVCC
FBN
ONINV VINV
-7.5V
MAX8614A
MAX8614B
GND PGND
ONBST
PVP
LXP
FBP
VBST
+15V
REF
SEQ
FLT
Typical Operating Circuit
Ordering Information
PART TEMP
RANGE
PIN-
PACKAGE
TOP
MARK
ILIM
BST/
INV
MAX8614AETD+ -40°C to
+85°C 14 TDFN ABG 0.44/
0.33
MAX8614BETD+ -40°C to
+85°C
14 TDFN ABH 0.8/
0.75
MAX8614BETD/V+ -40°C to
+85°C
14 TDFN AKT 0.8/
0.75
True Shutdown is a trademark of Maxim Integrated Products, Inc.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part that conforms to AEC-Q100.
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
2Maxim Integrated
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, AVCC to GND ..................................................-0.3V to +6V
LXN to VCC .............................................................-18V to +0.3V
LXP to PGND ..........................................................-0.3V to +33V
REF, ONINV, ONBST, SEQ, FBN, FBP
FLT to GND .........................................-0.3V to (AVCC + 0.3)V
PVP to GND................................................-0.3V to (VCC + 0.3)V
AVCC to VCC .........................................................-0.3V to +0.3V
PGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (TA= +70°C Multilayer Board)
14-Pin 3mm x 3mm TDFN (derate 18.2mW/°C above
TA= +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 = VAVCC = VONINV = 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 TA= +25°C.)
PARAMETER CONDITIONS MIN TYP MAX UNITS
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 VAVCC 24 V
Inverter Output-Voltage Adjust Range VINV - VCC (Note 2) -16 0 V
MAX8614B 0.7 0.8 0.9
LXP Current Limit MAX8614A 0.34 0.44 0.52
A
MAX8614B 0.90 1.05 1.20
LXP Short-Circuit Current Limit MAX8614A 0.52 0.61 0.70
A
MAX8614B 0.65 0.75 0.85
LXN Current Limit MAX8614A 0.28 0.33 0.38
A
LXN On-Resistance VCC = 3.6V 0.6 1.1
LXP On-Resistance VCC = 3.6V 0.625
PVP On-Resistance VCC = 3.6V 0.15 0.3
Maximum Duty Cycle Step-up and inverter 82 90 %
IAVCC 0.75 1.4
Quiescent Current (Switching, No Load) IVCC 2 3
mA
IAVCC 400 800
Quiescent Current (No Switching, No Load) IVCC 8 15
μA
TA= +25°C 0.1 5
Shutdown Supply Current TA= +85°C 0.1 μA
FBP Line Regulation VCC = 2.7V to 5.5V -20 mV/D
FBN Line Regulation VCC = 2.7V to 5.5V 20 mV/
(D - 0.5)
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
3
Maxim Integrated
ELECTRICAL CHARACTERISTICS (continued)
(VCC = VAVCC = VONINV = 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 TA= +25°C.)
PARAMETER CONDITIONS MIN TYP MAX UNITS
ILXP = IILIMMIN, MAX8614B -15
FBP Load Regulation ILXP = IILIMMIN, MAX8614A -35
mV/A
ILXN = IILIMMIN, MAX8614B 17.5
FBN Load Regulation ILXN = IILIMMIN, MAX8614A 65
mV/A
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 < IREF < 50μA 10 mV
REF Line Regulation 3.3V < VAVCC < 5.5V 2 5 mV
FBP Threshold Voltage No load 0.995 1.010 1.025 V
FBN Threshold Voltage No load -10 0 +10 mV
TA= +25°C -50 +5 +50
FBP Input Leakage Current VFBP =1.025V TA= +85°C +5 nA
TA= +25°C -50 +5 +50
FBN Input Leakage Current FBN = -10mV TA= +85°C +5 nA
TA= +25°C -5 +0.1 +5
LXN Input Leakage Current VLXN = -12V TA= +85°C +0.1 μA
TA= +25°C -5 +0.1 +5
LXP Input Leakage Current VLXP = 23V TA= +85°C +0.1 μA
TA= +25°C -5 +0.1 +5
PVP Input Leakage Current VPVP = 0V TA= +85°C +0.1 μA
TA= +25°C -1 +0.1 +1
FLT Input Leakage Current VFLT = 3.6V TA= +85°C +0.1 μA
FLT Input Resistance Fault mode, TA= +25°C 10 20
ONINV, ONBST, SEQ LOGIC INPUTS
Logic-Low Input 2.7V < VAVCC < 5.5V 0.5 V
Logic-High Input 2.7V < VAVCC < 5.5V 1.6 V
Bias Current TA= +25°C 0.1 1 μA
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
4Maxim Integrated
ELECTRICAL CHARACTERISTICS
(VCC = VAVCC = VONINV = 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)
PARAMETER CONDITIONS MIN TYP MAX UNITS
AVCC = VCC Voltage Range (Note 1) 3 5.5 V
UVLO Threshold VCC rising 2.42 2.82 V
Step-Up Output Voltage Adjust Range VAVCC 24 V
Inverter Output Voltage Adjust Range VINV - VCC (Note 2) -16 0 V
MAX8614B 0.7 0.9
LXP Current Limit MAX8614A 0.34 0.52 A
MAX8614B 0.9 1.2
LXP Short-Circuit Current Limit MAX8614A 0.52 0.70 A
MAX8614B 0.65 0.85
LXN Current Limit MAX8614A 0.28 0.38 A
LXN On-Resistance VCC = 3.6V 1.1
PVP On-Resistance VCC = 3.6V 0.3
Maximum Duty Cycle Step-up and inverter 82 %
IAVCC 1.4
Quiescent Current (Switching, No Load) IVCC 3
mA
IAVCC 800
Quiescent Current (No Switching, No Load) IVCC 15
μA
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 < VAVCC < 5.5V 0.5 V
Logic-High Input 2.7V < VAVCC < 5.5V 1.6 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 VCC, 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.
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
5
Maxim Integrated
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
MAX8614A/B toc01
2.5 3.0 3.5 4.0 4.5 5.0 5.5
0
50
100
150
200
250
300
350
VOUT = 20V
VOUT = 15V
VOUT = 10V
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA) .
MAX8614A/B toc02
2.5 3.0 3.5 4.0 4.5 5.0 5.5
0
50
100
150
200
250
300
VINV = -10V
VINV = -7.5V
VINV = -5V
POSITIVE OUTPUT EFFICIENCY
vs. OUTPUT CURRENT
OUTPUT CURRENT (mA)
EFFICIENCY (%)
MAX8614A/B toc03
0.1 1 10 100
L = 2.2μH, C = 2.2μF
0
10
20
30
40
50
60
70
80
90
100
VCC = 3V
VCC = 3.6V
VCC = 4.2V
VCC = 5V
POSITIVE OUTPUT EFFICIENCY
vs. OUTPUT CURRENT
OUTPUT CURRENT (mA)
EFFICIENCY (%)
MAX8614A/B toc04
0
10
20
30
40
50
60
70
80
90
100
0.1 1 10 100
L = 10μH, C = 10μF
VCC = 3V
VCC = 3.6V
VCC = 4.2V
VCC = 5V
NEGATIVE OUTPUT EFFICIENCY
vs. OUTPUT CURRENT
OUTPUT CURRENT (mA)
EFFICIENCY (%)
MAX8614A/B toc05
0
10
20
30
40
50
60
70
80
90
100
0.1 1 10 100
L = 4.7μH, C = 4.7μF
VCC = 3V
VCC = 3.6V
VCC = 4.2V
VCC = 5V
NEGATIVE OUTPUT EFFICIENCY
vs. OUTPUT CURRENT
OUTPUT CURRENT (mA)
EFFICIENCY (%)
MAX8614A/B toc06
0
10
20
30
40
50
60
70
80
90
100
0.1 1 10 100
L = 10μH, C = 10μF
VCC = 3V
VCC = 3.6V
VCC = 4.2V
VCC = 5V
OUTPUT EFFICIENCY
vs. OUTPUT CURRENT
OUTPUT CURRENT (mA)
EFFICIENCY (%)
MAX8614A/B toc07
0
10
20
30
40
50
60
70
80
90
100
0.1 1 10 100
BOTH OUTPUTS LOADED EQUALLY
L1 = 2.2μH, C1 = 2.2μF, L2 = 4.7μH, C2 = 4.7μF
VCC = 3V
VCC = 3.6V
VCC = 4.2V
VCC = 5V
OUTPUT EFFICIENCY
vs. OUTPUT CURRENT
OUTPUT CURRENT (mA)
EFFICIENCY (%)
MAX8614A/B toc08
0
10
20
30
40
50
60
70
80
90
100
0.1 1 10 100 1000
BOTH OUTPUTS LOADED EQUALLY
L1 = 10μH, C1 = 10μF, L2 = 10μH, C2 = 10μF
VCC = 3V
VCC = 3.6V
VCC = 4.2V
VCC = 5V
Typical Operating Characteristics
(TA= +25°C, VCC = VAVCC = 3.6V, SEQ = GND, Figure 1, unless otherwise noted.)
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
6Maxim Integrated
CHANGE IN OUTPUT VOLTAGE
vs. OUTPUT CURRENT (NEGATIVE OUTPUT)
OUTPUT CURRENT (mA)
CHANGE IN OUTPUT VOLTAGE (%)
MAX8614A/B toc10
0 25 50 75 100 125
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0
VIN = 5V
VOUT- = -7.5V
VIN = 4.2V
VIN = 3V
VIN = 3.6V
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
INPUT VOLTAGE (V)
SUPPLY CURRENT (µA)
MAX8614A/B toc11
2.5 3.0 3.5 4.0 4.5 5.0 5.5
0
100
200
300
400
500
600
700
800
900
1000
AVCC
VCC
SOFT-START WAVEFORMS
MAX8614A/B toc12
VONINV
5V/div
0V
10V/div
5V/div
100mA/div
0V
0V
VONBST
VBST
VINV
IIN
4ms/div
SEQ = GND
SOFT-START WAVEFORMS
MAX8614A/B toc13
VONINV
5V/div
0V
10V/div
5V/div
100mA/div
0V
0V
VONBST
VBST
VINV
IIN
4ms/div
SEQ = AVCC
LINE TRANSIENT
MAX8614A/B toc14
50mV/div
AC-COUPLED
50mV/div
AC-COUPLED
3.5V
VBST
VIN
3.5V TO 4.5V
TO 3.5V
VINV
40μs/div
Typical Operating Characteristics (continued)
(TA= +25°C, VCC = VAVCC = 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
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
7
Maxim Integrated
LOAD TRANSIENT (NEGATIVE OUTPUT)
MAX8614A/B toc16
50mV/div
AC-COUPLED
100mV/div
AC-COUPLED
50mA/div
0V
VBST
IINV
VINV
4μs/div
20mA TO 100mA
TO 20mA
SWITCHING WAVEFORMS (POSITIVE OUTPUT)
MAX8614A/B toc17
50mV/div
AC-COUPLED
10V/div
500mA/div
0A
0V
VBST
ILX
VLX
400ns/div
IBST = 20mA
SWITCHING WAVEFORMS (POSITIVE OUTPUT)
MAX8614A/B toc18
50mV/div
AC-COUPLED
10V/div
500mA/div
0A
0V
VBST
ILX
VLX
400ns/div
IBST = 50mA
SWITCHING WAVEFORMS (NEGATIVE OUTPUT)
MAX8614A/B toc19
50mV/div
AC-COUPLED
10V/div
500mA/div
0A
0V
VINV
ILX
VLX
400ns/div
IINV = 20mA
SWITCHING WAVEFORMS (NEGATIVE OUTPUT)
MAX8614A/B toc20
50mV/div
AC-COUPLED
10V/div
500mA/div
0A
0V
VINV
ILX
VLX
400ns/div
IINV = 100mA
LOAD TRANSIENT (POSITIVE OUTPUT)
MAX8614A/B toc15
20mV/div
AC-COUPLED
100mV/div
AC-COUPLED
20mA/div
0V
VBST
IBST
VINV
4μs/div
20mA TO 50mA
TO 20mA
Typical Operating Characteristics (continued)
(TA= +25°C, VCC = VAVCC = 3.6V, SEQ = GND, Figure 1, unless otherwise noted.)
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
8Maxim Integrated
Typical Operating Characteristics (continued)
(TA= +25°C, VCC = VAVCC = 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
VBST = +15V
IOUT = 50mA
VINV = -7.5V
IOUT = 100mA
PIN NAME FUNCTION
1 ONBST
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 AVCC 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.
6FLT Fault Open-Drain Output. Connect a 100k resistor from FLT to AVCC. 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 ONINV
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 PGND 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 VCC Power Input Supply. VCC supplies power for the step-up and inverting DC-DC converters. VCC must be
connected to AVCC.
14 LXN Negative Output Switching Inductor Node. LXN is high impedance in shutdown.
— EP Exposed Pad. Connect exposed pad to ground.
Pin Description
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
9
Maxim Integrated
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-width-
modulated (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/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.
LXN
VCC
PVP
REF
FBN
ONBST
MAX8614A
MAX8614B
LXP
SEQ
ONINV
AVCC
GND
PGND
FBP
1MHz
OSCILLATOR
REFERENCE
1.25V
STEP-UP
CURRENT SENSE
INVERTER
CURRENT SENSE
SOFT-START
ERROR
AMPLIFIER PWM
COMPARATOR
INVERTER
CONTROL
LOGIC
BIAS
AND
CONTROL
BLOCK
1.01V
ERROR
AMPLIFIER PWM
COMPARATOR STEP-UP
CONTROL
LOGIC
FLT
Functional Diagram
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
10 Maxim Integrated
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 current-
mode 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 over-
load 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 nega-
tive 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 power-
on 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 accom-
plished 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 refer-
ence 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 opera-
tion and MOSFET switching when AVCC 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 indepen-
dently 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
approximately 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 VCC 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
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
11
Maxim Integrated
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 cur-
rent 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 mini-
mal overshoot when a load is removed and minimal volt-
age 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 over-
shoot 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 microsec-
onds 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 30kΩto
100kΩrange. R1 is then given by:
where VFBP = 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 100kΩrange. R3 is then given by:
where VREF = 1.25V and VFBN = 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 skip-
ping 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 satura-
tion 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 representa-
tive 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 volt-
age exceeds the output voltage. Schottky diodes are
preferred due to their low forward voltage. However,
ultra-high-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 IBSTMAX ) / ( RCS D+ VBST2)
where RCS = 0.015 (MAX8614B), and 0.035 (MAX8614A),
and D+ is 1 minus the step-up switch duty cycle and is:
D+ = VCC/VBST
RVV
VV
FBN IMV
REF FBN
34=× −
−
⎛
⎝
⎜⎞
⎠
⎟
R
RV
V
BST
FBP
12 1=−
⎛
⎝
⎜⎞
⎠
⎟
R
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
12 Maxim Integrated
For stability, the inverter output filter capacitor (C2)
should satisfy the following:
C2 > (6L VREF IINVMAX )/
(RCS D- (VREF - VINV) VINV)
where RCS = 0.0175 (MAX8614B), and 0.040
(MAX8614A), and D- is 1 minus the inverter switch duty
cycle and is:
D- = VCC/VINV
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 AVCC separately from VCC
with a 1.0µF ceramic capacitor placed as close as pos-
sible to the AVCC 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.
Table 1. Inductor Selection Guide
OUTPUT VOLTAGES
AND LOAD CURRENT INDUCTOR L (μH) DCR (mΩ)I
SAT (A) SIZE (mm)
TOKO
DB3018C, 1069AS-2R0 2.0 72 1.4 3 x 3 x 1.8
TOKO
DB3018C, 1069AS-4R3 4.3 126 0.97 3 x 3 x 1.8
TOKO
S1024AS-4R3M 4.3 47 1.2 4 x 4 x 1.7
Sumida
CDRH2D14-4R7 4.7 170 1 3.2 x 3.2 x 1.55
15V, 50mA
-7.5V, 100mA
TOKO
S1024AS-100M 10 100 0.8 4 x 4 x 1.7
Sumida
CDRH2D11-100 10 400 0.35 3.2 x 3.2 x 1.2
Sumida
CDRH2D14-100 10 295 0.46 3.2 x 3.2 x 1.55
15V, 20mA
-7.5V, 40mA
Murata
LQH32CN100K33 10 300 0.45 3.2 x 2.5 x 2
Table 2. Component Suppliers
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)
631-435-1110 www.centralsemi.com
Motorola
(MBR0540L) 602-303-5454 www.motorola.com
CAPACITORS
Taiyo Yuden 408-573-4150 www.t-yuden.com
TDK 888-835-6646 www.TDK.com
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
13
Maxim Integrated
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 as possible to their respective feedback pins.
Place the input bypass capacitor as close as possible
to AVCC and GND.
LXN
VCC
PVP
C5
1.0μFC6
0.22μF
C4
22μF
C2
4.7μF
C3
1μF
C1
2.2μF
VBATT
(2.7V ~ 5V)
FAULT
VBATT
REF
FBN
14
12
10
8
R3
187kΩ
1%
R4
30.9kΩ
1%
R5
100kΩ
R1
1.4MΩ
1%
R2
100kΩ
1%
VINV
VBST
13
511
1
9
2
3
4
6
7
ONBST
ONINV
REF
VINV
-7.5V AT 100mA
D2
CMHSH5-21
D1
CMHSH5-21
MAX8614A
MAX8614B
LXP
SEQ
GND PGND
VBST
+15V AT 50mA
L2
4.7μH
L1
2.2μH
FBP
FLT
AVCC
Figure 1. Typical Application Circuit
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
14 Maxim Integrated
Package Information
For the latest package outline information and land patterns (foot-
prints), go to www.maximintegrated.com/packages. Note that a
“+”, “#”, or “-” in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but the
drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE OUTLINE NO. LAND
PATTERN NO.
14 TDFN T1433+2 21-0137 90-0063
Chip Information
PROCESS: BiCMOS
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000 ________________________________
15
© 2014 Maxim Integrated Products, Inc. Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
MAX8614A/MAX8614B
Dual-Output (+ and -) DC-DC
Converters for CCD
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
2 6/14 Added MAX8614ETD/V+ to Ordering Information 1
