General Description
The MAX8614A/MAX8614B dual-output step-up DC-DC
converters generate both a positive and negative sup-
ply 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 pow-
ering 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 out-
put down to 16V below the input voltage. The
MAX8614B has a higher current limit than the
MAX8614A. Both devices operate at a fixed 1MHz fre-
quency 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 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
♦Dual Output Voltages (+ and -)
♦Adjustable Up to +24V and Down to -10V at 5.5VIN
♦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 1; 9/06
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 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
PK G
C O D E
MAX8614AETD+
-40°C to
+85°C
14 TD FN
3m m x 3m m
( T1433- 2)
ABG 0.44/
0.33
T1433+
MAX8614BETD+
-40°C to
+85°C
14 TD FN
3m m x 3m m
( T1433- 2)
ABH 0.8/
0.75
T1433+
True Shutdown is a trademark of Maxim Integrated Products, Inc.
+Denotes lead-free package.
EVALUATION KIT
AVAILABLE
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, 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 Ω
LXP On-Resistance VCC = 3.6V
0.625
Ω
PVP On-Resistance VCC = 3.6V
0.15
0.3 Ω
Maximum Duty Cycle Step-up and inverter 82 90 %
IAVCC
0.75
1.4
Quiescent Current (Switching, No Load) IVCC 23
mA
IAVCC
400 800
Quiescent Current (No Switching, No Load)
IVCC 815µA
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
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
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°C1020Ω
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
4 _______________________________________________________________________________________
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 Ω
PVP On-Resistance VCC = 3.6V 0.3 Ω
Maximum Duty Cycle Step-up and inverter 82 %
IAVCC 1.4
Quiescent Current (Switching, No Load) IVCC 3mA
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
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
6 _______________________________________________________________________________________
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
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
8 _______________________________________________________________________________________
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 100kΩ 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 paddle to ground.
Pin Description
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-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 Response/Voltage Positioning section).
Step-Up Converter
The step-up converter generates a positive output volt-
age 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 inter-
nal load switch disconnects the battery from the load
by opening the battery connection to the inductor, pro-
viding 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 can-
not 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 ______________________________________________________________________________________
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-com-
pensation ramp. At the beginning of each clock cycle,
the internal power switch turns on until the PWM com-
parator 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-lock-
out (UVLO) circuitry, which prevents circuit operation
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 inter-
nally 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
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 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
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 cur-
rents. 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 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-tran-
sient 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 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,
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 fil-
ter 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).
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 ______________________________________________________________________________________
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). 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 lev-
els 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
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 AVCC and GND.
Chip Information
PROCESS: BiCMOS
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 ______________________________________________________________________________________
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.)
6, 8, &10L, DFN THIN.EPS
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 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 MIN. MAX.
A 0.70 0.80
D 2.90 3.10
E 2.90 3.10
A1 0.00 0.05
L 0.20 0.40
PKG. CODE N D2 E2 eJEDEC SPEC b[(N/2)-1] x e
PACKAGE VARIATIONS
0.25 MIN.k
A2 0.20 REF.
2.00 REF0.25–0.050.50 BSC2.30–0.1010T1033-1
2.40 REF0.20–0.05- - - - 0.40 BSC1.70–0.10 2.30–0.1014T1433-1
1.50–0.10 MO229 / WEED-3
0.40 BSC - - - - 0.20–0.05 2.40 REFT1433-2 14 2.30–0.101.70–0.10
T633-2 6 1.50–0.10 2.30–0.10 0.95 BSC MO229 / WEEA 0.40–0.05 1.90 REF
T833-2 8 1.50–0.10 2.30–0.10 0.65 BSC MO229 / WEEC 0.30–0.05 1.95 REF
T833-3 8 1.50–0.10 2.30–0.10 0.65 BSC MO229 / WEEC 0.30–0.05 1.95 REF
2.30–0.10 MO229 / WEED-3 2.00 REF0.25–0.050.50 BSC1.50–0.1010T1033-2
Revision History
Pages changed at Rev 1: 1, 12, 14, 15