General Description
The MAX8515A/MAX8515 shunt regulators simplify the
design of voltage regulation and overvoltage protection
(OVP) functions in high-accuracy isolated DC-to-DC con-
verters 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 volt-
age. 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 +25°C and 1% from -40°C to +85°C and provides
the output voltage regulation function for isolated DC-to-
DC converters. The MAX8515 features initial output
accuracy of 1% at +25°C and 1.8% from -40°C to +85°C
and can provide an output OVP function for isolated DC-
to-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 tran-
sistor 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 -40°C to +85°C extended temperature range. An eval-
uation kit is available to speed designs.
Applications
Isolated DC-to-DC Converters
Network, Telecom, and Cellular Base Station
Power Supplies
Low-Dropout Linear Regulators
Shunt Regulator
Adjustable Voltage Reference
Features
♦MAX8515A
0.6V ±0.5% Initial Accuracy at +25°C
0.6V ±1% Accuracy from -40°C to +85°C
♦MAX8515
0.6V ±1% Initial Accuracy at +25°C
0.6V ±1.8% Accuracy from -40°C to +85°C
♦Sinks 20mA at 0.2V to 18V
♦Input Voltage Range from 1.7V to 28V
♦Directly Drives Optocouplers
♦0.2ΩDynamic Output Impedance
♦Space-Saving 5-Pin SC70 or SOT23 Packages
MAX8515A/MAX8515
Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
________________________________________________________________ Maxim Integrated Products 1
19-2528; Rev 1; 2/03
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.
Ordering Information
PART TEMP RANGE PIN-PACKAGE
MAX8515AEXK-T -40°C to +85°C 5 SC70-5
MAX8515AEZK-T -40°C to +85°C 5 Thin SOT23-5
MAX8515EXK-T -40°C to +85°C 5 SC70-5
MAX8515EZK-T -40°C to +85°C 5 Thin SOT23-5
GND
INOUT
15FBPGND
MAX8515A
MAX8515
SC7O/THIN SOT23
TOP VIEW
2
34
Pin Configuration
MAX8515A
MAX8515
PRIMARY SIDE
PWM CONVERTER
INPUT SUPPLY
1.7V TO 28V
INPUT
1.7V TO 18V
ISOLATED DC-DC
CONVERTER
OUTPUT
(DOWN TO 0.6V)
OUT
FBGND
PGND
IN
CONTROL
VOLTAGE
Typical Operating Circuit
5
-
P
I
N
S
C
7
0
2
.
0
m
m
x
2
.
1
m
m
EVALUATION KIT
AVAILABLE
Functional Diagram appears at end of data sheet.
Selector Guide appears at end of data sheet.
MAX8515A/MAX8515
Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
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.
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 =+70°C)
5-Pin SC70 (derate 3.1mW/°C above +70°C)...........246.9mW
5-Pin Thin SOT23 (derate 9.1mW/°C above +70°C)....727mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature Range ............................-40°C to +150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
ELECTRICAL CHARACTERISTICS
(VIN = 3.3V, OUT = FB, IOUT = 5mA, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
IN
IN Voltage Range VIN 1.7 28 V
IOUT = 0.3mA 0.5 1
IN Supply Current IIN VIN = 2V to 28V IOUT = 10mA 2.5 4 mA
FB
MAX8515AE_K
0.597
0.6
0.603
TA = +25°CMAX8515E_K
0.594
0.6
0.606
MAX8515AE_K
0.595
0.6
0.605
TA = 0°C to +85°CMAX8515E_K
0.592
0.6
0.608
MAX8515AE_K
0.594
0.6
0.606
FB Threshold Accuracy
TA = -40°C to +85°CMAX8515E_K
0.589
0.6
0.608
V
FB Load Regulation IOUT = 1mA to 20mA 3.8 6 mV
VIN = 2V to 28V 0.2 1
FB Line Regulation VIN = 1.7V to 28V 1.5 mV
FB Output Voltage Regulation VOUT = 0.2V to 18V, IOUT = 1mA 0.2 1 mV
FB Input Bias Current
IFB
(
BIAS
)
VIN = 28V
-0.1 0.02 +0.1
µA
OUT
OUT Voltage Range VOUT 0.2 18 V
Maximum Output Current
IOUT
(
MAX
)
VOUT = 0.2V, VIN = 2V, VFB = 0.63V 20 mA
TA = +25°C
0.001
0.1
Output Leakage Current
IOUT
(
LEAK
)
VIN = 28V, VOUT = 18V,
VFB = 0V TA = +85°C
0.03
µA
Dynamic Output Impedance ZOUT IOUT = 1mA to 20mA, f <1kHz 0.2
0.32
Ω
Note 1: Devices are production tested at TA = +25°C, limits over temperature are guaranteed by design.
MAX8515A/MAX8515
Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
_______________________________________________________________________________________ 3
FB BIAS CURRENT (nA)
-25
-20
-15
-10
-5
0
-30
FB BIAS CURRENT
vs. TEMPERATURE
MAX8515 toc01
TEMPERATURE (°C)
6035-15 10-40 85
VIN = 3.3V
VIN = 10V
VIN = 28V
OUT-LEAKAGE CURRENT (nA)
0
5
10
15
20
25
30
35
40
-5
OUT-LEAKAGE CURRENT
vs. TEMPERATURE
MAX8515 toc02
TEMPERATURE (°C)
6035-15 10-40 85
VIN = 28V
VOUT = 18V
FB = GND
70 70
45
0
-45
-90
-135
-180
-30
0.1 1 10 100 1000
GAIN AND PHASE vs. FREQUENCY
VOUT = 0.6V
-10
MAX8515 toc03
FREQUENCY (kHz)
GAIN (dB)
PHASE (DEGREES)
10
30
50
40
20
0
-20
60
FIGURE 2
GAIN AND PHASE vs. FREQUENCY
VOUT = 6V
MAX8515 toc04
FREQUENCY (kHz)
GAIN (dB)
100101
-20
-10
0
10
20
30
40
-30
0.1 1000
FIGURE 2
45
0
-45
-90
-135
-180
90
PHASE (DEGREES)
OUTPUT VOLTAGE SLEW RATE
MAX8515 toc05
2µs/div
0.55V
0.66V
VOUT: 2V/div
VFB: 200mV/div
C2 = OPEN
SUPPLY CURRENT vs. LOAD CURRENT
MAX8515 toc07
LOAD CURRENT (mA)
SUPPLY CURRENT (mA)
15105
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
020
VIN = 28V
VIN = 10V
VIN = 3.3V
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX8515 toc06
FREQUENCY (Hz)
PSRR (dB)
1k100101
-70
-60
-50
-40
-30
-20
-10
0
10
-80
0.1 10k
TA = +25°C
TA = -40°C
TA = +25°C
TA = +85°C
Typical Operating Characteristics
(VIN = 3.3V, IOUT = 5mA, FB = OUT, circuit in Figure 1, C1 = 0.1µF, C2 = 1µF, TA = +25°C, unless otherwise specified.)
MAX8515A/MAX8515
Detailed Description
The MAX8515A/MAX8515 adjustable shunt regulators
feature isolated supply inputs and outputs, ideal for isolat-
ed 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.
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 1.0µF capacitor from OUT to GND
when the output voltage is 0.6V. A resistor-divider con-
nected from OUT to GND produces higher output volt-
ages and allows for a smaller output capacitor. The
value of the output capacitor is inversely proportional to
the output voltage:
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.
VR1
R2
CV
OUT
OUT
OUT
=×+
=×
06 1
106
.
.
µF
Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
4 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VIN = 3.3V, IOUT = 5mA, FB = OUT, circuit in Figure 1, C1 = 0.1µF, C2 = 1µF, TA = +25°C, unless otherwise specified.)
OUTPUT VOLTAGE CHANGE
vs. LOAD CURRENT
MAX8515 toc08
LOAD CURRENT (mA)
OUTPUT VOLTAGE CHANGE (%)
15105
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
-0.3
020
OUTPUT VOLTAGE CHANGE (%)
0
0.01
0.02
0.03
0.04
0.05
-0.01
OUTPUT VOLTAGE CHANGE
vs. INPUT VOLTAGE
MAX8515 toc09
INPUT VOLTAGE (V)
2318813328
PIN NAME FUNCTION
1 PGND Power Ground. Connect PGND and GND together.
2 GND Analog Ground. Connect GND and PGND together.
3 OUT Output. Connect a ceramic capacitor from OUT to GND. See the Applications Information section.
4 IN Supply Input. Connect a 0.1µF capacitor to GND.
5 FB Feedback Input. Regulates to 600mV.
Pin Description
Optical Feedback
Setting VOUT
Figure 3 displays an application circuit using the
MAX8515A/MAX8515 in an opto-isolated feedback cir-
cuit. The maximum bias current for the photodiode is
set with R1. The isolated DC-to-DC converter compen-
sation 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:
Set R4 to 10kΩand calculate R3 by:
For example, given a regulator output voltage of 1.8V
and R4 = 10kΩ, R3 is found to be 20kΩ.
Compensation Circuit
A typical compensation scheme is depicted in Figure 3.
C3 provides an integrator function that minimizes out-
put regulation error.
R2 provides additional phase compensation at the zero
frequency fz:
The midband gain is given by:
Add C4 for high-frequency noise rejection. Determine
R2 based on the midband gain required by the isolated
power supply. Choose fzbased on the power supply
small-signal transfer function. Calculate C3 once fz
is known.
AR
=2
R3
fZ2R2C3
=××
1
π
R3 V
V-
OUT
FB
=
×14 R
VR3
R4
REG =×+
06 1.
MAX8515A/MAX8515
Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
_______________________________________________________________________________________ 5
Figure 1. MAX8515A/MAX8515 Typical Application Circuit,
Shunt Regulator/Adjustable Voltage Reference
MAX8515A
MAX8515
C1
0.1µF
OUT
FBGND
IN
VIN
1.8V
VOUT
0.6V/20mA
R1 = SHORT
R2 = OPEN
C2
1.0µF
R1
R3
R2
PGND VIN (V)
3.3
10
28
R3 (Ω)
135
470
1.33k
Figure 2. Test Circuits for Gain and Phase Plots
MAX8515A
MAX8515
0.1µF
OUT
FBGND
IN
3.3V
5.6V
GAIN = TEST/REFERENCE
NETWORK
ANALYZER
SOURCE
0.82µF
50kΩ
1kΩ
VOUT = 0.6V
TEST CIRCUIT
1MΩ
1MΩ
2.2nF
2.2nF
TEST
PGND
MAX8515A
MAX8515
0.1µF
OUT
FBGND
IN
3.3V
11V
GAIN = TEST/REFERENCE
REFERENCE
REFERENCE
NETWORK
ANALYZER
SOURCE
50kΩ
115kΩ
1%
VOUT = 6V
TEST CIRCUIT
1MΩ
0.1µF
10kΩ
1%
90.1kΩ
1%
1MΩ
160kΩ
2.2nF
2.2nF
TEST
PGND
MAX8515A/MAX8515
Overvoltage Protection
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; 10kΩis recom-
mended for R4. Then, R3 = 6.2kΩ.
where VOVP = 0.8V x 1.25 for the given example.
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:
Choose R1 to maintain load regulation up to a 2A load.
Use the following equation:
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 βis the minimum current gain
of Q1 at rated load current. VIN is the minimum input volt-
age at IN. For the typical application circuit, VIN_MIN =
2.375V, VREG = 1.0V, VBE = 0.65V, and β= 180. Choose
R1 = 15Ωfor fast transient response. C1 is the input
decoupling capacitor and C2 is the compensation
capacitor. Use a 1µF, 6.3V capacitor for this application.
Figure 6 shows a typical load-regulation curve for the cir-
cuit in Figure 5. This circuit does not provide short-circuit,
overcurrent, or overtemperature protection.
R1 V-V-V
I
IN_MIN REG BE
O_MAX
=×β
VR2
R3
REG =×+
06 1.V
R3 V
V-
OVP
FB
=
×14R
Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
6 _______________________________________________________________________________________
Figure 4. MAX8515A/MAX8515 Typical Application Circuit,
OVP Circuit (Set to 1V OVP Threshold for 0.8V Nominal Output)
MAX8515A
MAX8515
OUT
0.8V
DC-DC OUTPUT
6V TO 10V
C1
0.1µF
16V
FB
R3
6.2kΩ
1%
R4
10kΩ
1%
R1
1.2kΩ
R2
2kΩ
GND
PGND
IN
FEEDBACK
OPTOCOUPLER
Figure 3. MAX8515A/MAX8515 Typical Application Circuit,
Opto-Feedback Circuit
MAX8515A
MAX8515
OUT
C1
0.1µF
VREG
1.8V
C2
0.1µF
FB
R3
20kΩ
1%
R4
10kΩ
1%
R1
47kΩ
R2
C3
GND
PGND
IN
MAX5003
V+
CONPGND
NDRV
INPUT
SUPPLY
C4
Chip Information
TRANSISTOR COUNT: 50
PROCESS: BiCMOS
MAX8515A/MAX8515
Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
_______________________________________________________________________________________ 7
Figure 6. Load Regulation of Linear-Regulator Circuit
LINEAR-REGULATOR
LOAD REGULATION
LOAD CURRENT (A)
OUTPUT VOLTAGE (mV)
1.51.00.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0
-3.5
0 2.0
-4.0
-4.5
-5.0
VCC = 1.2V
VCC = 2.5V
CVCC = 220µF
Figure 5. MAX8515A/MAX8515 Typical Application Circuit,
Linear Regulator
MAX8515A
MAX8515
Q1
FZT1049A
C2
1.0µF
C1
0.1µF
OUT
FBGND
IN
VCC
1.2V TO
2.5V
VIN
R2
6.65kΩ
R1
R3
10kΩ
IO
2A (MAX)
VREG
1V
VIN (V)
2.5
3.3
5
R1 (Ω)
22.1
40.2
82.5
MAX8515A
MAX8515
OUT
PGND
0.6V
REFERENCE
FB
GND
IN
Functional Diagram
Selector Guide
PART INITIAL ACCURACY TOP MARKS
MAX8515AEXK-T 0.6V, 0.5% feedback ADX
MAX8515AEZK-T 0.6V, 0.5% feedback ADRK
MAX8515EXK-T 0.6V, 1% feedback ADY
MAX8515EZK-T 0.6V, 1% feedback ADRL
MAX8515A/MAX8515
Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
8 _______________________________________________________________________________________
SC70, 5L.EPS
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.)
MAX8515A/MAX8515
Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
_______________________________________________________________________________________ 9
THIN SOT23.EPS
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
Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
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
© 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
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.)
