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19-4014; Rev 0; 3/06
Dual-Output (+ and -) DC-DC Converters for CCD
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 ShutdownTM, 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 -40C to +85C extended temperature range. 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 1A Shutdown Current 1MHz Fixed-Frequency PWM Operation Fault-Condition Flag Thermal Shutdown Small, 3mm x 3mm, 14-Pin TDFN Package
Features
MAX8614A/MAX8614B
Ordering Information
PART TEMP PINRANGE PACKAGE 14 TDFN -40C to 3mm x 3mm +85C (T1433-2) TOP MARK ABG ILIM BST/INV 0.44/0.33
MAX8614AETD+
Applications
CCD Bias Supplies and OLED Displays Digital Cameras Camcorders and Portable Multimedia PDAs and Smartphones
14 TDFN -40C to 3mm x 3mm +85C (T1433-2) +Denotes lead-free package. MAX8614BETD+
ABH
0.8/0.75
Typical Operating Circuit
INPUT (2.7V TO 5.5V)
True Shutdown is a trademark of Maxim Integrated Products, Inc.
Pin Configuration
ONINV PGND PVP LXN
VCC ONINV ONBST
LXN
VINV -7.5V
TOP VIEW
SEQ
LXP
VCC
AVCC
14
13
12
11
10
9
8
REF AVCC SEQ
MAX8614A MAX8614B
FBN PVP
REF
MAX8614A MAX8614B
+
1 ONBST 2 FBN 3 AVCC 4 REF 5 GND 6 FLT 7 FBP
LXP FLT GND PGND FBP
VBST +15V
TDFN ________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Dual-Output (+ and -) DC-DC Converters for CCD MAX8614A/MAX8614B
ABSOLUTE MAXIMUM RATINGS
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 = +70C Multilayer Board) 14-Pin 3mm x 3mm TDFN (derate 18.2mW/C above TA = +70C) ............................................................1454.4mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC = VAVCC = VONINV = VONBST = 3.6V, PGND = SEQ = GND, C6 = 0.22F, C1 = 2.2F, C2 = 4.7F, Figure 1, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER AVCC and VCC Voltage Range UVLO Threshold UVLO Hysteresis Step-Up Output Voltage Adjust Range Inverter Output Voltage Adjust Range LXP Current Limit LXP Short-Circuit Current Limit LXN Current Limit LXN On-Resistance LXP On-Resistance PVP On-Resistance Maximum Duty Cycle Quiescent Current (Switching, No Load) Quiescent Current (No Switching, No Load) Shutdown Supply Current FBP Line Regulation FBN Line Regulation VINV - VCC (Note 2) MAX8614B MAX8614A MAX8614B MAX8614A MAX8614B MAX8614A VCC = 3.6V VCC = 3.6V VCC = 3.6V Step-up and inverter IAVCC IVCC IAVCC IVCC TA = +25C TA = +85C VCC = 2.7V to 5.5V VCC = 2.7V to 5.5V 82 VAVCC -16 0.7 0.34 0.90 0.52 0.65 0.28 0.8 0.44 1.05 0.61 0.75 0.33 0.6 0.625 0.15 90 0.75 2 400 8 0.1 0.1 -20 20 1.4 3 800 15 5 0.3 (Note 1) VCC rising CONDITIONS MIN 2.7 2.42 2.55 25 24 0 0.9 0.52 1.20 0.70 0.85 0.38 1.1 TYP MAX 5.5 2.66 UNITS V V mV V V A A A % mA A A mV/D mV/ (D - 0.5)
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Dual-Output (+ and -) DC-DC Converters for CCD
ELECTRICAL CHARACTERISTICS (continued)
(VCC = VAVCC = VONINV = VONBST = 3.6V, PGND = SEQ = GND, C6 = 0.22F, C1 = 2.2F, C2 = 4.7F, Figure 1, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER FBP Load Regulation FBN Load Regulation Oscillator Frequency Soft-Start Interval Overload-Protection Fault Delay FBP, FBN, REFERENCE REF Output Voltage REF Load Regulation REF Line Regulation FBP Threshold Voltage FBN Threshold Voltage FBP Input Leakage Current FBN Input Leakage Current LXN Input Leakage Current LXP Input Leakage Current PVP Input Leakage Current FLT Input Leakage Current FLT Input Resistance ONINV, ONBST, SEQ LOGIC INPUTS Logic-Low Input Logic-High Input Bias Current 2.7V < VAVCC < 5.5V 2.7V < VAVCC < 5.5V TA = +25C 1.6 0.1 1 0.5 V V A No load 0A < IREF < 50A 3.3V < VAVCC < 5.5V No load No load VFBP =1.025V FBN = -10mV VLXN = -12V VLXP = 23V VPVP = 0V VFLT = 3.6V TA = +25C TA = +85C TA = +25C TA = +85C TA = +25C TA = +85C TA = +25C TA = +85C TA = +25C TA = +85C TA = +25C TA = +85C -1 -5 -5 -5 -50 0.995 -10 -50 1.24 1.25 10 2 1.010 0 +5 +5 +5 +5 +0.1 +0.1 +0.1 +0.1 +0.1 +0.1 +0.1 +0.1 10 20 +1 +5 +5 +5 +50 5 1.025 +10 +50 1.26 V mV mV V mV nA nA A A A A Step-up and inverter CONDITIONS ILXP = IILIMMIN, MAX8614B ILXP = IILIMMIN, MAX8614A ILXN = IILIMMIN, MAX8614B ILXN = IILIMMIN, MAX8614A 0.93 MIN TYP -15 -35 17.5 65 1 10 100 1.07 MAX UNITS mV/A mV/A MHz ms ms
MAX8614A/MAX8614B
Fault mode, TA = +25C
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Dual-Output (+ and -) DC-DC Converters for CCD MAX8614A/MAX8614B
ELECTRICAL CHARACTERISTICS
(VCC = VAVCC = VONINV = VONBST = VEN = 3.6V, PGND = SEQ = GND, C6 = 0.22F, C1 = 2.2F, C2 = 6.7F, Figure 1, TA = -40C to +85C, unless otherwise noted.) (Note 3)
PARAMETER AVCC = VCC Voltage Range UVLO Threshold Step-Up Output Voltage Adjust Range Inverter Output Voltage Adjust Range LXP Current Limit LXP Short-Circuit Current Limit LXN Current Limit LXN On-Resistance PVP On-Resistance Maximum Duty Cycle Quiescent Current (Switching, No Load) Quiescent Current (No Switching, No Load) Oscillator Frequency FBP, FBN, REFERENCE REF Output Voltage FBP Threshold Voltage FBN Threshold Voltage ONINV, ONBST SEQ LOGIC INPUTS Logic-Low Input Logic-High Input 2.7V < VAVCC < 5.5V 2.7V < VAVCC < 5.5V 1.6 0.5 V V No load No load No load 1.235 0.995 -10 1.260 1.025 +10 V V mV VINV - VCC (Note 2) MAX8614B MAX8614A MAX8614B MAX8614A MAX8614B MAX8614A VCC = 3.6V VCC = 3.6V Step-up and inverter IAVCC IVCC IAVCC IVCC 0.93 82 1.4 3 800 15 1.07 (Note 1) VCC rising CONDITIONS MIN 3 2.42 VAVCC -16 0.7 0.34 0.9 0.52 0.65 0.28 TYP MAX 5.5 2.82 24 0 0.9 0.52 1.2 0.70 0.85 0.38 1.1 0.3 UNITS V V V V A A A % mA A MHz
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 -40C are guaranteed by design, not production tested.
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Dual-Output (+ and -) DC-DC Converters for CCD
Typical Operating Characteristics
(TA = +25C, VCC = VAVCC = 3.6V, SEQ = GND, Figure 1, unless otherwise noted.)
MAX8614A/MAX8614B
MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE
MAX8614A/B toc01
MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE
MAX8614A/B toc02
POSITIVE OUTPUT EFFICIENCY vs. OUTPUT CURRENT
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 L = 2.2H, C = 2.2F 0.1 1 10 OUTPUT CURRENT (mA) 100 VCC = 3V VCC = 3.6V VCC = 4.2V VCC = 5V
MAX8614A/B toc03
350 MAXIMUM OUTPUT CURRENT (mA) 300 VOUT = 10V 250 200 150 100 50 VOUT = 20V 0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) 5.0 VOUT = 15V
300 MAXIMUM OUTPUT CURRENT (mA) . 250 200 150 100 VINV = -10V 50 0 VINV = -7.5V VINV = -5V
100
0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) 5.0 5.5
5.5
POSITIVE OUTPUT EFFICIENCY vs. OUTPUT CURRENT
MAX8614A/B toc04
NEGATIVE OUTPUT EFFICIENCY vs. OUTPUT CURRENT
MAX8614A/B toc05
NEGATIVE OUTPUT EFFICIENCY vs. OUTPUT CURRENT
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 VCC = 4.2V VCC = 5V VCC = 3.6V VCC = 3V
MAX8614A/B toc06
100 90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 0.1
VCC = 5V
100 90 80 70 EFFICIENCY (%) 60 50 40 30 20
VCC = 3.6V VCC = 3V
100
VCC = 3.6V VCC = 4.2V
VCC = 3V
VCC = 4.2V VCC = 5V
L = 10H, C = 10F 1 10 OUTPUT CURRENT (mA) 100
10 0 0.1 L = 4.7H, C = 4.7F 1 10 OUTPUT CURRENT (mA) 100
0 0.1
L = 10H, C = 10F 1 10 OUTPUT CURRENT (mA) 100
OUTPUT EFFICIENCY vs. OUTPUT CURRENT
MAX8614A/B toc07
OUTPUT EFFICIENCY vs. OUTPUT CURRENT
VCC = 5V 90 80 70 EFFICIENCY (%) VCC = 4.2V VCC = 3V VCC = 3.6V
MAX8614A/B toc08
100 90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 0.1 1 10 OUTPUT CURRENT (mA) BOTH OUTPUTS LOADED EQUALLY L1 = 2.2H, C1 = 2.2F, L2 = 4.7H, C2 = 4.7F VCC = 3.6V VCC = 3V VCC = 4.2V VCC = 5V
100
60 50 40 30 20 10 0
BOTH OUTPUTS LOADED EQUALLY L1 = 10H, C1 = 10F, L2 = 10H, C2 = 10F 0.1 1 10 100 OUTPUT CURRENT (mA) 1000
100
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Dual-Output (+ and -) DC-DC Converters for CCD MAX8614A/MAX8614B
Typical Operating Characteristics (continued)
(TA = +25C, VCC = VAVCC = 3.6V, SEQ = GND, Figure 1, unless otherwise noted.)
CHANGE IN OUTPUT VOLTAGE vs. LOAD CURRENT (POSITIVE OUTPUT)
MAX8614A/B toc09
CHANGE IN OUTPUT VOLTAGE vs. OUTPUT CURRENT (NEGATIVE OUTPUT)
VOUT- = -7.5V CHANGE IN OUTPUT VOLTAGE (%) -0.5 -1.0 -1.5 -2.0 -2.5 VIN = 3V -3.0 -3.5 VIN = 3.6V 0 25 50 75 100 OUTPUT CURRENT (mA) 125 VIN = 5V VIN = 4.2V
MAX8614A/B toc10
0 CHANGE IN OUTPUT VOLTAGE (%) -0.5 -1.0 -1.5 -2.0 -2.5 -3.0 -3.5 0 25 50 75 100 LOAD CURRENT (mA) 125 VCC = 3V VCC = 3.6V VCC = 5V VCC = 4.2V
0
150
NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE
MAX8614A/B toc11
SOFT-START WAVEFORMS
MAX8614A/B toc12
1000 900 800 SUPPLY CURRENT (A) 700 600 500 400 300 200 100 0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) 5.0 VCC AVCC
VONINV VONBST
SEQ = GND 5V/div 0V 10V/div 0V
VBST
VINV
5V/div
IIN 100mA/div 0V 5.5 4ms/div
SOFT-START WAVEFORMS
MAX8614A/B toc13
LINE TRANSIENT
MAX8614A/B toc14
VONINV VONBST
SEQ = AVCC 5V/div 0V 10V/div 0V VBST 50mV/div AC-COUPLED
VBST
VINV
5V/div
VIN 3.5V TO 4.5V TO 3.5V
3.5V
IIN 100mA/div 0V 4ms/div
VINV
50mV/div AC-COUPLED 40s/div
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Dual-Output (+ and -) DC-DC Converters for CCD MAX8614A/MAX8614B
Typical Operating Characteristics (continued)
(TA = +25C, VCC = VAVCC = 3.6V, SEQ = GND, Figure 1, unless otherwise noted.)
LOAD TRANSIENT (POSITIVE OUTPUT)
MAX8614A/B toc15
LOAD TRANSIENT (NEGATIVE OUTPUT)
MAX8614A/B toc16
VINV
20mV/div AC-COUPLED
VBST
50mV/div AC-COUPLED
VBST
100mV/div AC-COUPLED
VINV
100mV/div AC-COUPLED
IBST 20mA TO 50mA TO 20mA 4s/div
20mA/div 0V
IINV
50mA/div 20mA TO 100mA TO 20mA 4s/div 0V
SWITCHING WAVEFORMS (POSITIVE OUTPUT)
MAX8614A/B toc17
SWITCHING WAVEFORMS (POSITIVE OUTPUT)
MAX8614A/B toc18
VBST
50mV/div AC-COUPLED 10V/div 0V
VBST
50mV/div AC-COUPLED 10V/div
VLX
VLX
0V
ILX IBST = 20mA 400ns/div
500mA/div 0A
ILX IBST = 50mA 400ns/div
500mA/div 0A
SWITCHING WAVEFORMS (NEGATIVE OUTPUT)
MAX8614A/B toc19
SWITCHING WAVEFORMS (NEGATIVE OUTPUT)
MAX8614A/B toc20
VINV
50mV/div AC-COUPLED 10V/div
VINV
50mV/div AC-COUPLED 10V/div
VLX
0V
VLX
0V
ILX IINV = 20mA 400ns/div
500mA/div 0A
ILX IINV = 100mA 400ns/div
500mA/div 0A
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Dual-Output (+ and -) DC-DC Converters for CCD MAX8614A/MAX8614B
Typical Operating Characteristics (continued)
(TA = +25C, VCC = VAVCC = 3.6V, SEQ = GND, Figure 1, unless otherwise noted.)
REFERENCE VOLTAGE vs. TEMPERATURE
MAX8614A/B toc21
SWITCHING FREQUENCY vs. TEMPERATURE
1.005 1.004 FREQUENCY (kHz) 1.003 1.002 1.001 1.000 0.999 0.998 0.997 0.996 VBST = +15V IOUT = 50mA VINV = -7.5V IOUT = 100mA
MAX8614A/B toc22
1.2490 1.2485 REFERENCE VOLTAGE (V) 1.2480 1.2475 1.2470 1.2465 1.2460 1.2455 1.2450 -40 -15 10 35 TEMPERATURE (C) 60
1.006
85
-40
-15
10 35 TEMPERATURE (C)
60
85
Pin Description
PIN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 -- NAME ONBST FBN AVCC REF GND FLT FBP SEQ ONINV LXP PGND PVP VCC LXN EP FUNCTION 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. 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. Bias Supply. AVCC powers the IC. AVCC must be connected to VCC. 1.25V Reference Voltage Output. Bypass with a 0.22F ceramic capacitor to GND. Ground. Connect GND to PGND with a short trace. 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. Positive Output-Voltage Feedback Input. Connect a resistor-divider between the positive output and GND with the center to FBP to set the positive output voltage. FBP is high impedance in shutdown. Sequence Logic Input. When SEQ = low, power-on sequence can be independently controlled by ONBST and ONINV. When SEQ = high, the positive output powers up before the negative output. Enable Logic Input. Connect ONINV to AVCC for automatic startup of the inverter, or use ONINV as an independent control of the inverter. Positive Output Switching Inductor Node. LXP is high impedance in shutdown. Power Ground. Connect PGND to GND with a short trace. 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. Power Input Supply. VCC supplies power for the step-up and inverting DC-DC converters. VCC must be connected to AVCC. Negative Output Switching Inductor Node. LXN is high impedance in shutdown. Exposed Pad. Connect exposed paddle to ground.
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Dual-Output (+ and -) DC-DC Converters for CCD
Functional Diagram
MAX8614A/MAX8614B
ERROR AMPLIFIER
PWM COMPARATOR INVERTER CONTROL LOGIC
MAX8614A MAX8614B
VCC
LXN
INVERTER CURRENT SENSE FBN ONBST ONINV FLT SEQ AVCC 1MHz OSCILLATOR PVP ERROR AMPLIFIER PWM COMPARATOR LXP STEP-UP CONTROL LOGIC PGND STEP-UP CURRENT SENSE FBP BIAS AND CONTROL BLOCK REFERENCE 1.25V REF
1.01V
SOFT-START
GND
Detailed Description
The MAX8614A/MAX8614B generate both a positive and negative output voltage by combining a step-up and an inverting DC-DC converter on one IC. Both the step-up converter and the inverter share a common clock. Each output is independently regulated. Each output is separately controlled by a pulse-widthmodulated (PWM) current-mode regulator. This allows the converters to operate at a fixed frequency (1MHz) for use in noise-sensitive applications. The 1MHz switching rate allows for small external components. Both converters are internally compensated and are optimized for fast transient response (see the LoadTransient 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.
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Dual-Output (+ and -) DC-DC Converters for CCD MAX8614A/MAX8614B
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%. 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.
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.
Undervoltage Lockout (UVLO)
The MAX8614A/MAX8614B feature undervoltage-lockout (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 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.
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 +170C (typ) the device shuts down. When it cools down by 20C (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 0.1A and both output loads are disconnected from the input supply.
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
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
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Dual-Output (+ and -) DC-DC Converters for CCD
the inverter output, load disconnect is implemented by turning off the inverter's internal power switch.
MAX8614A/MAX8614B
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.
V - VIMV R 3 = R4 x FBN VREF - VFBN where VREF = 1.25V and VFBN = 0V.
Inductor Selection
The MAX8614A/MAX8614B high switching frequency allows for the use of a small inductor. The 4.7H and 2.2H inductors shown in the Typical Operating Circuit is recommended for most applications. Larger inductances reduce the peak inductor current, but may result in skipping pulses at light loads. Smaller inductances require less board space, but may cause greater peak current due to current-sense comparator propagation delay. Use inductors with a ferrite core or equivalent. Powder iron cores are not recommended for use with high switching frequencies. The inductor's incremental saturation rating must exceed the selected current limit. For highest efficiency, use inductors with a low DC resistance (under 200m); however, for smallest circuit size, higher resistance is acceptable. See Table 1 for a representative list of inductors and Table 2 for component suppliers.
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.
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.
Applications Information
Adjustable Output Voltage
The positive output voltage is set by connecting FBP to a resistive voltage-divider between the output and GND (Figure 1). Select feedback resistor R2 in the 30k to 100k range. R1 is then given by: V R1 = R2 BST - 1 VFBP 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 30k to 100k range. R3 is then given by:
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). D+ is 1 minus the step-up switch duty cycle and is: D+ = VCC / VBST
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11
Dual-Output (+ and -) DC-DC Converters for CCD MAX8614A/MAX8614B
Table 1. Inductor Selection Guide
OUTPUT VOLTAGES AND LOAD CURRENT INDUCTOR TOKO DB3018C, 1069AS-2R0 TOKO DB3018C, 1069AS-4R3 15V, 50mA -7.5V, 100mA TOKO S1024AS-4R3M Sumida CDRH2D14-4R7 TOKO S1024AS-100M Sumida CDRH2D11-100 15V, 20mA -7.5V, 40mA Sumida CDRH2D14-100 Murata LQH32CN100K33 L (H) 2.0 4.3 4.3 4.7 10 10 10 10 DCR (m) 72 126 47 170 100 400 295 300 ISAT (A) 1.4 0.97 1.2 1 0.8 0.35 0.46 0.45 SIZE (mm) 3 x 3 x 1.8 3 x 3 x 1.8 4 x 4 x 1.7 3.2 x 3.2 x 1.55 4 x 4 x 1.7 3.2 x 3.2 x 1.2 3.2 x 3.2 x 1.55 3.2 x 2.5 x 2
Table 2. Component Suppliers
SUPPLIER INDUCTORS Murata Sumida TOKO DIODES Central Semiconductor (CMHSH5-2L) Motorola (MBR0540L) CAPACITORS Taiyo Yuden TDK 408-573-4150 www.t-yuden.com 888-835-6646 www.TDK.com 631-435-1110 www.centralsemi.com 602-303-5454 www.motorola.com 770-436-1300 www.murata.com 847-545-600 www.sumida.com 847-297-0070 www.tokoam.com PHONE WEBSITE
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 4.7F, 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 AVCC separately from VCC with a 0.1F ceramic capacitor placed as close as possible to the AVCC and GND pins.
For stability, the inverter output filter capacitor, C2, should satisfy the following: C2 > (6L VREF IINVMAX ) / (RCS D- (VREF - VINV) VINV) where R CS = 0.0175 (MAX8614B), and 0.040 (MAX8614A). D- is 1 minus the inverter switch duty cycle and is:
12
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.
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Dual-Output (+ and -) DC-DC Converters for CCD MAX8614A/MAX8614B
VBATT (2.7V ~ 5V) VINV R3 187k 1% R4 30.9k 1% REF 3 C5 0.1F 4 C6 0.22F AVCC REF PVP C4 4.7F 13 VCC 1 ONBST 9 ONINV 2 FBN LXN 14 D2 CMHSH5-21
L2 4.7H
VINV C2 -7.5V AT 100mA 4.7F
MAX8614A MAX8614B
12 C3 1F L1 2.2H LXP 10 D1 CMHSH5-21
VBATT R5 100k FAULT
6 FLT VBST R1 1.4M 1% R2 100k 1%
VBST C1 +15V AT 50mA 2.2F
7
FBP GND 5 PGND 11
SEQ
8
Figure 1. Typical Application Circuit
It is important to connect the GND pin, the input bypass-capacitor ground lead, and the output filter capacitor ground lead to a single point (star ground configuration) to minimize ground noise and improve regulation. Also, minimize lead lengths to reduce stray capacitance, trace resistance, and radiated noise, with preference given to the feedback circuit, the ground
circuit, and LX_. Place feedback resistors R1-R4 as close to their respective feedback pins as possible. Place the input bypass capacitor as close as possible to AVCC and GND.
Chip Information
PROCESS: BiCMOS
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13
Dual-Output (+ and -) DC-DC Converters for CCD 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.)
D2 D A2
N
PIN 1 ID
0.35x0.35 b
PIN 1 INDEX AREA
E DETAIL A
E2 e
[(N/2)-1] x e REF.
A1
k
C L
C L
A
L e e
L
PACKAGE OUTLINE, 6,8,10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm
-DRAWING NOT TO SCALE-
21-0137
G
1
2
14
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6, 8, &10L, DFN THIN.EPS
Dual-Output (+ and -) DC-DC Converters for CCD
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
MAX8614A/MAX8614B MAX8614A/MAX8614B
COMMON DIMENSIONS SYMBOL A D E A1 L k A2 MIN. 0.70 2.90 2.90 0.00 MAX. 0.80 3.10 3.10 0.05
0.20 0.40 0.25 MIN. 0.20 REF.
PACKAGE VARIATIONS PKG. CODE T633-1 T633-2 T833-1 T833-2 T833-3 T1033-1 T1433-1 T1433-2 N 6 6 8 8 8 10 14 14 D2 1.500.10 1.500.10 1.500.10 1.500.10 1.500.10 1.500.10 1.700.10 1.700.10 E2 2.300.10 2.300.10 2.300.10 2.300.10 2.300.10 2.300.10 2.300.10 2.300.10 e 0.95 BSC 0.95 BSC 0.65 BSC 0.65 BSC 0.65 BSC 0.50 BSC 0.40 BSC 0.40 BSC JEDEC SPEC MO229 / WEEA MO229 / WEEA MO229 / WEEC MO229 / WEEC MO229 / WEEC MO229 / WEED-3 ------b 0.400.05 0.400.05 0.300.05 0.300.05 0.300.05 0.250.05 0.200.05 0.200.05 [(N/2)-1] x e 1.90 REF 1.90 REF 1.95 REF 1.95 REF 1.95 REF 2.00 REF 2.40 REF 2.40 REF
DOWNBONDS ALLOWED
NO NO NO NO YES NO YES NO
PACKAGE OUTLINE, 6,8,10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm
-DRAWING NOT TO SCALE-
21-0137
G
2
2
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 (c) 2006 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.

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