ML4865ES-2 Micro Linear, ML4865ES-2 Datasheet - Page 6

• Manufacturer Part Number: ML4865ES-2
• Description: High Voltage High Current Boost Regulator
• Manufacturer: Micro Linear

ML4865
DESIGN CONSIDERATIONS
INPUT VOLTAGE RANGE
The input voltage range determines whether an external
Schottky diode is necessary or optional. If the input
voltage is 6V or lower, the ML4865 can be operated as a
stand alone boost regulator with a shutdown that fully
isolates the input from the output. Adding an optional
Schottky diode extends the input voltage range up to 10V,
and improves the efficiency and the output current
capability. However, the external diode now provides a
leakage path from the input to the output during
shutdown.
OUTPUT CURRENT CAPABILITY
The maximum current available at the output of the
regulator is related to the maximum inductor current by
the ratio of the input to output voltage and the full load
efficiency. The maximum inductor current is dependent on
the input voltage. The full load efficiency may be as low
as 65% when the ML4865 is used without a Schottky
diode and can exhibit an input voltage dependence when
an external diode is used. The maximum output current
can be determined by using the typical performance
curves shown in Figures 4 and 5, or by calculation using
the following empirical equation:
Where, for applications using the internal synchronous
rectifier:
And for applications using an external Schottky:
The curves and the equations are based on the operating
circuit shown in Figure 7. It is recommended to verify the
current capability and efficiency for the components
selected.
6
I
I
I
h
I
I
h
OUT MAX
OUT MAX
OUT MAX
IN
IN
=
=
=
=
(
0 65
0 025
(
(
0 05
0 07
.
.
.
.
)
)
)
@
@
´
@
´
´
V
V
V
V
V
V
V
OUT
IN
V
IN
V
IN
OUT
IN
OUT
IN
IN
+
+
+
™
0 4
0 4
0 65
™
´
.
.
0 07
.
I
IN
.
0 05
™
.
™
h
V
IN
´
(A)
V
+
IN
0 4
.
+
™
0 4
.
0 025
.
´
0 65
.
™
V
IN
+
0 65
(1)
.
Figure 6. No Load Input Current vs. Input Voltage for the
Figure 4. Output Current vs. Input Voltage
Figure 5. Efficiency vs. Output Current
900
700
500
300
100
100
300
250
200
150
100
90
80
70
60
50
50
0
0
0
1
0
V IN = 10V
V IN = 5V
V IN = 2V
WITHOUT
EXTERNAL
SCHOTTKY
Circuit of Figure 7
2
2
10
4
4
I OUT (mA)
V IN (V)
V IN (V)
SCHOTTKY
WITHOUT
EXTERNAL
SCHOTTKY
EXTERNAL
6
6
WITH
100
with Schottky
without Schottky
SCHOTTKY
EXTERNAL
V OUT = 12V
WITH
8
8
1000
10
10