19-2528; Rev 1; 2/03
IT
TION K
VALUA
E
BLE
AVAILA
Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
General Description
Features
o
MAX8515A
0.6V
±0.5%
Initial Accuracy at +25°C
0.6V
±1%
Accuracy from -40°C to +85°C
o
MAX8515
0.6V
±1%
Initial Accuracy at +25°C
0.6V
±1.8%
Accuracy from -40°C to +85°C
o
Sinks 20mA at 0.2V to 18V
o
Input Voltage Range from 1.7V to 28V
o
Directly Drives Optocouplers
o
0.2Ω 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 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.
Ordering Information
PART
MAX8515AEXK-T
MAX8515AEZK-T
MAX8515EXK-T
MAX8515EZK-T
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
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
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.
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 (V
IN
+0.3V)
PGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (T
A
=+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
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
(V
IN
= 3.3V, OUT = FB, I
OUT
= 5mA, T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
IN
IN Voltage Range
IN Supply Current
FB
T
A
= +25°C
FB Threshold Accuracy
T
A
= 0°C to +85°C
T
A
= -40°C to +85°C
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
V
OUT
I
OUT(MAX)
V
OUT
= 0.2V, V
IN
= 2V, V
FB
= 0.63V
T
A
= +25°C
V = 28V, V
OUT
= 18V,
I
OUT(LEAK) IN
V
FB
= 0V
T
A
= +85°C
Z
OUT
I
OUT
= 1mA to 20mA, f <1kHz
0.2
20
0.001
0.03
0.2
0.32
0.1
18
V
mA
µA
Ω
I
FB(BIAS)
I
OUT
= 1mA to 20mA
V
IN
= 2V to 28V
V
IN
= 1.7V to 28V
V
OUT
= 0.2V to 18V, I
OUT
= 1mA
V
IN
= 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
µA
V
V
IN
I
IN
V
IN
= 2V to 28V
I
OUT
= 0.3mA
I
OUT
= 10mA
1.7
0.5
2.5
28
1
4
V
mA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Note 1:
Devices are production tested at T
A
= +25°C, limits over temperature are guaranteed by design.
2
_______________________________________________________________________________________
Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
Typical Operating Characteristics
(V
IN
= 3.3V, I
OUT
= 5mA, FB = OUT, circuit in Figure 1, C1 = 0.1µF, C2 = 1µF, T
A
= +25°C, 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)
V
IN
= 28V
V
OUT
= 18V
FB = GND
MAX8515 toc02
GAIN AND PHASE vs. FREQUENCY
V
OUT
= 0.6V
70
60
50
40
30
20
10
0
-10
-20
-30
FIGURE 2
0.1
1
10
FREQUENCY (kHz)
100
0
-5
V
IN
= 3.3V
FB BIAS CURRENT (nA)
-10
-15
-20
V
IN
= 28V
-25
-30
-40
-15
10
35
60
V
IN
= 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
V
OUT
= 6V
40
30
20
GAIN (dB)
10
MAX8515 toc04
OUTPUT VOLTAGE SLEW RATE
90
45
PHASE (DEGREES)
0
-45
MAX8515 toc05
V
OUT
: 2V/div
0
-10
-20
-30
0.1
1
10
FREQUENCY (kHz)
100
FIGURE 2
-90
-135
-180
1000
0.66V
0.55V
V
FB
: 200mV/div
C2 = OPEN
2µs/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
V
IN
= 28V
V
IN
= 10V
V
IN
= 3.3V
MAX8515 toc07
10
0
-10
-20
PSRR (dB)
-30
-40
-50
-60
-70
-80
0.1
1
10
100
1k
T
A
= -40°C
T
A
= +25°C
T
A
= +85°C
T
A
= +25°C
4.0
10k
0
0
5
10
LOAD CURRENT (mA)
15
20
FREQUENCY (Hz)
_______________________________________________________________________________________
3
Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
MAX8515A/MAX8515
Typical Operating Characteristics (continued)
(V
IN
= 3.3V, I
OUT
= 5mA, FB = OUT, circuit in Figure 1, C1 = 0.1µF, C2 = 1µF, T
A
= +25°C, 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 0.1µF capacitor to GND.
Feedback Input. Regulates to 600mV.
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
V
OUT
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 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:
R1
V
OUT
=
0.6
×
1
+
R2
0.6
C
OUT
=
1
µF ×
V
OUT
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 1.0µF capacitor from OUT to GND
4
_______________________________________________________________________________________
Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
MAX8515A/MAX8515
V
IN
1.8V
R3
V
OUT
0.6V/20mA
OUT
MAX8515A
MAX8515
PGND
GND
FB
R2
R1 = SHORT
R2 = OPEN
C2
1.0µF
V
IN
(V) R3 (Ω)
135
3.3
470
10
1.33k
28
0.1µF
IN
MAX8515A
MAX8515
PGND
GND
FB
2.2nF
REFERENCE
1MΩ
NETWORK
ANALYZER
SOURCE
3.3V
V
OUT
= 0.6V
TEST CIRCUIT
OUT
0.82µF
50kΩ
5.6V
1kΩ
2.2nF
TEST
1MΩ
IN
C1
0.1µF
R1
Figure 1. MAX8515A/MAX8515 Typical Application Circuit,
Shunt Regulator/Adjustable Voltage Reference
GAIN = TEST/REFERENCE
Optical Feedback
Setting V
OUT
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
V
REG
with the following equation:
R3
V
REG
=
0.6
×
1
+
R4
Set R4 to 10kΩ and calculate R3 by:
V
R3
=
OUT
- 1
×
R4
V
FB
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 f
z
:
1
f
Z
=
2
π ×
R2
×
C3
GAIN = TEST/REFERENCE
115kΩ
1%
3.3V
V
OUT
= 6V
TEST CIRCUIT
IN
0.1µF
MAX8515A
MAX8515
PGND
GND
FB
OUT
11V
TEST
2.2nF
1MΩ
160kΩ
0.1µF
50kΩ
90.1kΩ
1%
NETWORK
ANALYZER
SOURCE
2.2nF
REFERENCE
10kΩ
1%
1MΩ
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 f
z
based on the power supply
small-signal transfer function. Calculate C3 once f
z
is known.
_______________________________________________________________________________________
5
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