MAX8515 MAXIM [Maxim Integrated Products], MAX8515 Datasheet - Page 6

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

Wide-Input 0.6V Shunt Regulators for
Isolated DC-to-DC Converters
Figure 3. MAX8515A/MAX8515 Typical Application Circuit,
Opto-Feedback Circuit
Figure 4. MAX8515A/MAX8515 Typical Application Circuit,
OVP Circuit (Set to 1V OVP Threshold for 0.8V Nominal Output)
6
0.1µF
C1
_______________________________________________________________________________________
V
1.8V
REG
0.1µF
16V
2kΩ
C1
6V TO 10V
R2
IN
PGND
GND
MAX8515A
MAX8515
IN
PGND
GND
47kΩ
R1
MAX8515A
MAX8515
1.2kΩ
OUT
R1
FB
20kΩ
OUT
1%
R3
FB
10kΩ
1%
R4
NDRV
PGND
MAX5003
OPTOCOUPLER
FEEDBACK
C2
0.1µF
V+
DC-DC OUTPUT
CON
0.8V
R2
C3
R4
10kΩ
1%
R3
6.2kΩ
1%
C4
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; 10kΩ is recom-
mended for R4. Then, R3 = 6.2kΩ.
where V
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 I
which is 2A in this application circuit. V
voltage of the linear regulator. V
forward voltage of Q1, and β is the minimum current gain
of Q1 at rated load current. V
age at IN. For the typical application circuit, V
2.375V, V
R1 = 15Ω for 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.
O_MAX
OVP
REG
= 0.8V x 1.25 for the given example.
= 1.0V, V
R1
is the rated maximum output current,
V
=
REG
R3
V
IN_MIN
=
=
BE



0 6
Overvoltage Protection
V
. V
= 0.65V, and β = 180. Choose
V
I
OVP
O_MAX
FB
- V
IN
×
REG
is the minimum input volt-
-
BE



1
1

 ×

Linear Regulator
- V
+
is the base-to-emitter
R2
R3
BE
R
REG
4



× β
is the output
IN_MIN
=