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19-2528; Rev 1; 2/03
KIT ATION EVALU ABLE AVAIL
Wide-Input 0.6V Shunt Regulators for Isolated DC-to-DC Converters
General Description Features
o MAX8515A 0.6V 0.5% Initial Accuracy at +25C 0.6V 1% Accuracy from -40C to +85C o MAX8515 0.6V 1% Initial Accuracy at +25C 0.6V 1.8% Accuracy from -40C to +85C o Sinks 20mA at 0.2V to 18V o Input Voltage Range from 1.7V to 28V o Directly Drives Optocouplers o 0.2 Dynamic Output Impedance o Space-Saving 5-Pin SC70 or SOT23 Packages
MAX8515A/MAX8515
The MAX8515A/MAX8515 shunt regulators simplify the design of voltage regulation and overvoltage protection (OVP) functions in high-accuracy isolated DC-to-DC converters with output voltages as low as 0.6V. The devices have supply voltage and feedback inputs separated from the output shunt stage, and can operate directly from the DC-to-DC converter output stage when the output voltage is 1.8V to 18V. Alternately, the MAX8515A/MAX8515 input stage can be biased from an unregulated 1.7V to 28V supply, independent of DC-to-DC converter output voltage. The MAX8515A/MAX8515 shunts 20mA when the output voltage is as low as 0.2V. The MAX8515A features an initial output accuracy of 0.5% at +25C and 1% from -40C to +85C and provides the output voltage regulation function for isolated DC-toDC converters. The MAX8515 features initial output accuracy of 1% at +25C and 1.8% from -40C to +85C and can provide an output OVP function for isolated DCto-DC converters. High open-loop bandwidth allows design of high-bandwidth DC-to-DC converters. Low-cost, low-dropout linear regulators can be designed with the MAX8515A/MAX8515 and an external NPN transistor for cost-conscious applications that do not require overcurrent, short-circuit, or overtemperature protection. The MAX8515/MAX8515A are available in space-saving 5-pin SC70 and SOT23 packages and are specified over the -40C to +85C extended temperature range. An evaluation kit is available to speed designs.
Ordering Information
PART MAX8515AEXK-T MAX8515AEZK-T MAX8515EXK-T MAX8515EZK-T TEMP RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C PIN-PACKAGE 5 SC70-5 5 Thin SOT23-5 5 SC70-5 5 Thin SOT23-5
Functional Diagram appears at end of data sheet. Selector Guide appears at end of data sheet.
Applications
Isolated DC-to-DC Converters Network, Telecom, and Cellular Base Station Power Supplies Low-Dropout Linear Regulators Shunt Regulator Adjustable Voltage Reference
Typical Operating Circuit
INPUT SUPPLY INPUT 1.7V TO 28V 1.7V TO 18V PRIMARY SIDE PWM CONVERTER CONTROL VOLTAGE IN OUT
Pin Configuration
TOP VIEW
PGND 1 5 FB
GND 2
m
m x 2.1
mm
MAX8515A MAX8515
4 IN
5
N SC7 -PI
MAX8515A MAX8515 PGND GND
0
FB
OUT 3
ISOLATED DC-DC CONVERTER OUTPUT (DOWN TO 0.6V)
2.0
SC7O/THIN SOT23
________________________________________________________________ Maxim Integrated Products
1
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Wide-Input 0.6V Shunt Regulators for Isolated DC-to-DC Converters MAX8515A/MAX8515
ABSOLUTE MAXIMUM RATINGS
IN to GND ...............................................................-0.3V to +30V OUT to GND ...........................................................-0.3V to +20V FB to GND .................-0.3V to the lower of 5.5V and (VIN +0.3V) PGND to GND .......................................................-0.3V to +0.3V Continuous Power Dissipation (TA =+70C) 5-Pin SC70 (derate 3.1mW/C above +70C) ...........246.9mW 5-Pin Thin SOT23 (derate 9.1mW/C above +70C) ....727mW Operating Temperature Range ...........................-40C to +85C Junction Temperature Range ............................-40C to +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
(VIN = 3.3V, OUT = FB, IOUT = 5mA, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER IN IN Voltage Range IN Supply Current FB TA = +25C FB Threshold Accuracy TA = 0C to +85C TA = -40C to +85C FB Load Regulation FB Line Regulation FB Output Voltage Regulation FB Input Bias Current OUT OUT Voltage Range Maximum Output Current Output Leakage Current Dynamic Output Impedance VOUT IOUT(MAX) VOUT = 0.2V, VIN = 2V, VFB = 0.63V IOUT(LEAK) ZOUT VIN = 28V, VOUT = 18V, VFB = 0V TA = +25C TA = +85C 0.2 20 0.001 0.03 0.2 0.32 0.1 18 V mA A IFB(BIAS) IOUT = 1mA to 20mA VIN = 2V to 28V VIN = 1.7V to 28V VOUT = 0.2V to 18V, IOUT = 1mA VIN = 28V -0.1 0.2 0.02 MAX8515AE_K MAX8515E_K MAX8515AE_K MAX8515E_K MAX8515AE_K MAX8515E_K 0.597 0.594 0.595 0.592 0.594 0.589 0.6 0.6 0.6 0.6 0.6 0.6 3.8 0.2 0.603 0.606 0.605 0.608 0.606 0.608 6 1 1.5 1 +0.1 mV mV mV A V VIN IIN VIN = 2V to 28V IOUT = 0.3mA IOUT = 10mA 1.7 0.5 2.5 28 1 4 V mA SYMBOL CONDITIONS MIN TYP MAX UNITS
IOUT = 1mA to 20mA, f <1kHz
Note 1: Devices are production tested at TA = +25C, limits over temperature are guaranteed by design.
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Wide-Input 0.6V Shunt Regulators for Isolated DC-to-DC Converters
Typical Operating Characteristics
(VIN = 3.3V, IOUT = 5mA, FB = OUT, circuit in Figure 1, C1 = 0.1F, C2 = 1F, TA = +25C, unless otherwise specified.)
FB BIAS CURRENT vs. TEMPERATURE
MAX8515 toc01
MAX8515A/MAX8515
OUT-LEAKAGE CURRENT vs. TEMPERATURE
35 OUT-LEAKAGE CURRENT (nA) 30 25 20 15 10 5 0 GAIN (dB) VIN = 28V VOUT = 18V FB = GND
MAX8515 toc02
GAIN AND PHASE vs. FREQUENCY VOUT = 0.6V
70 60 50 40 30 20 10 0 -10 -20 -30 FIGURE 2 0.1 1 10 FREQUENCY (kHz) 100
0 -5 VIN = 3.3V FB BIAS CURRENT (nA) -10 -15 -20 VIN = 28V -25 -30 -40 -15 10 35 60 VIN = 10V
MAX8515 toc03
40
70 45 0 -45 -90 -135 PHASE (DEGREES)
-5 85 -40 -15 10 35 60 85 TEMPERATURE (C) TEMPERATURE (C)
-180 1000
GAIN AND PHASE vs. FREQUENCY VOUT = 6V
40 30 20 GAIN (dB) 10
MAX8515 toc04
OUTPUT VOLTAGE SLEW RATE
90 45 PHASE (DEGREES) 0 -45
MAX8515 toc05
VOUT: 2V/div
0 -10 -20 -30 0.1 1 10 FREQUENCY (kHz) 100 FIGURE 2 -90 -135 -180 1000
0.66V 0.55V VFB: 200mV/div C2 = OPEN 2s/div
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
MAX8515 toc06
SUPPLY CURRENT vs. LOAD CURRENT
3.5 SUPPLY CURRENT (mA) 3.0 2.5 2.0 1.5 1.0 0.5 VIN = 28V VIN = 10V VIN = 3.3V
MAX8515 toc07
10 0 -10 -20 PSRR (dB) -30 -40 -50 -60 -70 -80 0.1 1 10 100 1k TA = -40C TA = +25C TA = +85C TA = +25C
4.0
10k
0 0 5 10 LOAD CURRENT (mA) 15 20
FREQUENCY (Hz)
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Wide-Input 0.6V Shunt Regulators for Isolated DC-to-DC Converters MAX8515A/MAX8515
Typical Operating Characteristics (continued)
(VIN = 3.3V, IOUT = 5mA, FB = OUT, circuit in Figure 1, C1 = 0.1F, C2 = 1F, TA = +25C, unless otherwise specified.)
OUTPUT VOLTAGE CHANGE vs. LOAD CURRENT
0.5 OUTPUT VOLTAGE CHANGE (%) 0.4 0.3 0.2 0.1 0 -0.1 -0.2 -0.3 0 5 10 LOAD CURRENT (mA) 15 20 -0.01 3 8 13 18 23 28 INPUT VOLTAGE (V)
MAX8515 toc08
OUTPUT VOLTAGE CHANGE vs. INPUT VOLTAGE
MAX8515 toc09
0.6
0.05 0.04 0.03 0.02 0.01 0
OUTPUT VOLTAGE CHANGE (%)
Pin Description
PIN 1 2 3 4 5 NAME PGND GND OUT IN FB FUNCTION Power Ground. Connect PGND and GND together. Analog Ground. Connect GND and PGND together. Output. Connect a ceramic capacitor from OUT to GND. See the Applications Information section. Supply Input. Connect a 0.1F capacitor to GND. Feedback Input. Regulates to 600mV.
Detailed Description
The MAX8515A/MAX8515 adjustable shunt regulators feature isolated supply inputs and outputs, ideal for isolated power-supply applications using an optocoupler in the feedback path. The MAX8515A/MAX8515 sink 20mA with VOUT at 0.2V. The wide input supply range allows the device to operate from 1.7V to 28V. The MAX8515A/ MAX8515 compare the FB input to a precision 600mV reference. If the FB input is low, OUT sinks no current. If FB rises above 600mV, OUT sinks up to 20mA.
when the output voltage is 0.6V. A resistor-divider connected from OUT to GND produces higher output voltages and allows for a smaller output capacitor. The value of the output capacitor is inversely proportional to the output voltage: R1 VOUT = 0.6 x 1 + R2 0.6 COUT = 1F x VOUT Set the current limit with a resistor connected from IN to OUT. This type of shunt regulator is limited to low-current applications. The MAX8515A/MAX8515 can typically sink up to 20mA in this application. Figure 2 shows the test circuits for gain and phase plots.
Applications Information
Shunt Regulator/Adjustable Voltage Reference
Figure 1 shows the MAX8515A/MAX8515 configured as a shunt regulator. Connect FB to OUT for an output voltage of 0.6V. Connect a 1.0F capacitor from OUT to GND
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Wide-Input 0.6V Shunt Regulators for Isolated DC-to-DC Converters MAX8515A/MAX8515
VIN 1.8V R3 VOUT 0.6V/20mA OUT MAX8515A MAX8515 PGND GND FB R2 R1 = SHORT R2 = OPEN C2 1.0F VIN (V) R3 () 135 3.3 470 10 1.33k 28 0.1F IN MAX8515A MAX8515 PGND GND FB 2.2nF REFERENCE 1M NETWORK ANALYZER SOURCE 3.3V VOUT = 0.6V TEST CIRCUIT OUT 0.82F 50k 5.6V
1k 2.2nF
TEST 1M
IN C1 0.1F
R1
Figure 1. MAX8515A/MAX8515 Typical Application Circuit, Shunt Regulator/Adjustable Voltage Reference
GAIN = TEST/REFERENCE
Optical Feedback
Setting VOUT Figure 3 displays an application circuit using the MAX8515A/MAX8515 in an opto-isolated feedback circuit. The maximum bias current for the photodiode is set with R1. The isolated DC-to-DC converter compensation circuit is formed with R2, C3, and C4. Resistors R3 and R4 set the isolated DC-to-DC converter output voltage. C1 decouples the input supply and C2 is needed to stabilize the MAX8515A/MAX8515. Calculate VREG with the following equation: R3 VREG = 0.6 x 1 + R4 Set R4 to 10k and calculate R3 by: V R3 = OUT - 1 x R4 VFB For example, given a regulator output voltage of 1.8V and R4 = 10k, R3 is found to be 20k. Compensation Circuit A typical compensation scheme is depicted in Figure 3. C3 provides an integrator function that minimizes output regulation error. R2 provides additional phase compensation at the zero frequency fz: 1 fZ = 2 x R2 x C3
GAIN = TEST/REFERENCE 115k 1% 3.3V VOUT = 6V TEST CIRCUIT IN 0.1F MAX8515A MAX8515 PGND GND FB OUT
11V
TEST 2.2nF 1M 160k
0.1F 50k 90.1k 1% NETWORK ANALYZER SOURCE
2.2nF REFERENCE 10k 1% 1M
Figure 2. Test Circuits for Gain and Phase Plots
The midband gain is given by: R2 A= R3 Add C4 for high-frequency noise rejection. Determine R2 based on the midband gain required by the isolated power supply. Choose fz based on the power supply small-signal transfer function. Calculate C3 once f z is known.
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Wide-Input 0.6V Shunt Regulators for Isolated DC-to-DC Converters MAX8515A/MAX8515
Overvoltage Protection
VREG 1.8V V+ MAX5003 NDRV PGND CON R1 47k INPUT SUPPLY
Figure 4 shows an isolated OVP circuit. R1 limits the current supplied to the photodiode. R2 limits the MAX8515A/MAX8515 input current. R3 and R4 set the trip threshold for the OVP. C1 is the input supply decoupling capacitor. Values for R3 and R4 are chosen based on the needed OVP threshold. For example, a trip threshold of 25% above the rated output voltage is needed for an OVP circuit. The values of R3 can be determined from the following equation once R4 is chosen; 10k is recommended for R4. Then, R3 = 6.2k. V R3 = OVP - 1 x R4 VFB
IN C1 0.1F MAX8515A MAX8515 PGND GND
OUT R3 20k 1% FB R4 10k 1% C2 0.1F R2 C4
where VOVP = 0.8V x 1.25 for the given example.
C3
Linear Regulator
Use an external pass transistor in conjunction with the MAX8515A/MAX8515 to create a linear regulator as shown in Figure 5. Determine the output voltage of the regulator by: R2 VREG = 0.6V x 1 + R3 Choose R1 to maintain load regulation up to a 2A load. Use the following equation:
Figure 3. MAX8515A/MAX8515 Typical Application Circuit, Opto-Feedback Circuit
6V TO 10V R1 1.2k
R1 =
FEEDBACK OPTOCOUPLER DC-DC OUTPUT 0.8V
VIN_MIN - VREG - VBE IO_MAX
x
R2 2k IN C1 0.1F 16V MAX8515A MAX8515 PGND GND OUT
R3 6.2k 1% FB R4 10k 1%
where IO_MAX is the rated maximum output current, which is 2A in this application circuit. VREG is the output voltage of the linear regulator. VBE is the base-to-emitter forward voltage of Q1, and is the minimum current gain of Q1 at rated load current. VIN is the minimum input voltage at IN. For the typical application circuit, VIN_MIN = 2.375V, VREG = 1.0V, VBE = 0.65V, and = 180. Choose R1 = 15 for fast transient response. C1 is the input decoupling capacitor and C2 is the compensation capacitor. Use a 1F, 6.3V capacitor for this application. Figure 6 shows a typical load-regulation curve for the circuit in Figure 5. This circuit does not provide short-circuit, overcurrent, or overtemperature protection.
Figure 4. MAX8515A/MAX8515 Typical Application Circuit, OVP Circuit (Set to 1V OVP Threshold for 0.8V Nominal Output)
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Wide-Input 0.6V Shunt Regulators for Isolated DC-to-DC Converters
VCC 1.2V TO 2.5V Q1 FZT1049A IO 2A (MAX) VREG 1V IN 0.6V REFERENCE R1 VIN IN C1 0.1F MAX8515A MAX8515 GND FB R3 10k VIN (V) 2.5 3.3 5 R1 () 22.1 40.2 82.5 OUT C2 1.0F R2 6.65k MAX8515A MAX8515 OUT
Functional Diagram
MAX8515A/MAX8515
FB
GND
PGND
Selector Guide
PART MAX8515AEXK-T MAX8515AEZK-T MAX8515EXK-T MAX8515EZK-T INITIAL ACCURACY 0.6V, 0.5% feedback 0.6V, 0.5% feedback 0.6V, 1% feedback 0.6V, 1% feedback TOP MARKS ADX ADRK ADY ADRL
Figure 5. MAX8515A/MAX8515 Typical Application Circuit, Linear Regulator
Chip Information
LINEAR-REGULATOR LOAD REGULATION
0 -0.5 -1.0 OUTPUT VOLTAGE (mV) -1.5 -2.0 -2.5 -3.0 -3.5 -4.0 -4.5 -5.0 0 0.5 1.0 LOAD CURRENT (A) 1.5 2.0 CVCC = 220F VCC = 1.2V VCC = 2.5V
TRANSISTOR COUNT: 50 PROCESS: BiCMOS
Figure 6. Load Regulation of Linear-Regulator Circuit
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Wide-Input 0.6V Shunt Regulators for Isolated DC-to-DC Converters MAX8515A/MAX8515
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.)
SC70, 5L.EPS
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Wide-Input 0.6V Shunt Regulators for Isolated DC-to-DC Converters
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.)
MAX8515A/MAX8515
_______________________________________________________________________________________
THIN SOT23.EPS
9
Wide-Input 0.6V Shunt Regulators for Isolated DC-to-DC Converters MAX8515A/MAX8515
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.)
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.
10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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