MAX8515 MAXIM [Maxim Integrated Products], MAX8515 Datasheet - Page 5

• Manufacturer Part Number: MAX8515
• Description: Wide-Input 0.6V Shunt Regulators for Isolated DC-to-DC Converters
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 1. MAX8515A/MAX8515 Typical Application Circuit,
Shunt Regulator/Adjustable Voltage Reference
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
Set R4 to 10kΩ and calculate R3 by:
For example, given a regulator output voltage of 1.8V
and R4 = 10kΩ, R3 is found to be 20kΩ.
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
REG
0.1µF
with the following equation:
C1
1.8V
V
IN
z
:
IN
PGND
GND
f
Z
MAX8515A
V
MAX8515
_______________________________________________________________________________________
R3
=
REG
R3
2
=
π
=



OUT
0 6
×
V
FB
.
Wide-Input 0.6V Shunt Regulators for
V
OUT
R2
FB
1
×
×



-
1
Compensation Circuit
1
C3
R1
R2
Optical Feedback

 ×

+
R3
R4
C2
1.0µF
R
4



V
0.6V/20mA
R1 = SHORT
R2 = OPEN
V
Setting V
OUT
IN
3.3
10
28
(V)
Isolated DC-to-DC Converters
R3 (Ω)
1.33k
135
470
OUT
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 f
small-signal transfer function. Calculate C3 once f
is known.
Figure 2. Test Circuits for Gain and Phase Plots
0.1µF
0.1µF
3.3V
3.3V
GAIN = TEST/REFERENCE
GAIN = TEST/REFERENCE
IN
PGND
GND
IN
PGND
GND
TEST CIRCUIT
TEST CIRCUIT
V
MAX8515A
MAX8515A
V
OUT
MAX8515
MAX8515
OUT
= 0.6V
= 6V
OUT
OUT
FB
FB
10kΩ
A
1%
z
=
based on the power supply
115kΩ
R
R3
1kΩ
1MΩ
2
0.1µF
0.82µF
1%
2.2nF
90.1kΩ
5.6V
1%
50kΩ
11V
REFERENCE
50kΩ
2.2nF
2.2nF
TEST
TEST
160kΩ
1MΩ
2.2nF
1MΩ
1MΩ
REFERENCE
ANALYZER
NETWORK
SOURCE
ANALYZER
NETWORK
SOURCE
5
z