ML4865 Просмотр технического описания (PDF) - Fairchild Semiconductor
Номер в каталоге
Компоненты Описание
Список матч
ML4865 Datasheet PDF : 10 Pages
| |||
ML4865
900
WITH
EXTERNAL
SCHOTTKY
700
500
300
WITHOUT
100
EXTERNAL
SCHOTTKY
0
0
2
4
6
8
10
VIN (V)
Figure 4. Output Current vs. Input Voltage
100
VIN = 10V
90
VOUT = 12V
80 VIN = 5V
70
VIN = 2V
60
with Schottky
without Schottky
50
1
10
100
1000
IOUT (mA)
Figure 5. Efficiency vs. Output Current
300
250
200
WITH
150
EXTERNAL
SCHOTTKY
100
50 WITHOUT
EXTERNAL
SCHOTTKY
0
0
2
4
6
VIN (V)
8
10
Figure 6. No Load Input Current vs.
Input Voltage for the Circuit of Figure 7
6
PRODUCT SPECIFICATION
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.
VIN
C1
47µF
ML4865
SENSE
GND
VOUT
SHDN
VIN
VL2
VL1 PWR GND
R1
1MΩ
22µH
(Sumida CD75)
D1
MBR0520L
VOUT
C2
47µF
Figure 7. Typical Application Circuit
Inductor Selection
The ML4865 is able to operate over a wide range of inductor
values. A value of 22µH or 33µH is a good choice, but any
value between 15µH and 50µH is acceptable. As the inductor
value is changed the control circuitry will automatically
adjust to keep the inductor current under control. Choosing
an inductance value of less than 15µH will reduce the com-
ponent’s footprint, but the efficiency and maximum output
current may drop.
It is important to use an inductor that is rated to handle 1.5A
peak currents without saturating. Also look for an inductor
with low winding resistance. A good rule of thumb is to
allow 5 to 10mΩ of resistance for each µH of inductance.
The final selection of the inductor will be based on trade-offs
between size, cost and efficiency. Inductor tolerance, core
and copper loss will vary with the type of inductor selected
and should be evaluated with a ML4865 under worst case
conditions to determine its suitability.
Several manufacturers supply standard inductance values in
surface mount packages:
Coilcraft
(847) 639-6400
Coiltronics
(561) 241-7876
Dale
(605) 665-9301
Sumida
(847) 956-0666
Output Capacitor
The output capacitor filters the pulses of current from the
switching regulator. Since the switching frequency will vary
with inductance, the minimum output capacitance required
to reduce the output ripple to an acceptable level will be a
function of the inductor used. Therefore, to maintain an out-
put voltage with less than 100mV of ripple (due to capaci-
tance) at full load current, use the following equation:
COUT
= 10 × L
VOUT
(F)
(2)
REV. 1.0.2 8/10/01
Share Link: 