FAN2564(2009) Просмотр технического описания (PDF) - Fairchild Semiconductor
Номер в каталоге
Компоненты Описание
Список матч
FAN2564 Datasheet PDF : 13 Pages
| |||
Application Information
Enable and Soft Start
A 1.4 MΩ pull-down resistor ensures the EN pin to be in
LOW state when it is floating. The chip is in shut-down
mode when EN pin is LOW.
To enable the chip, the EN pin needs to be raised higher
than 0.95V. The output pin starts to charge up to the
final voltage. On-chip soft-start circuitry limits the peak
inrush current through VIN pin to less than the specified
typical value of 500mA, regardless of COUT value and
load conditions.
The startup time increases as VOUT, COUT, and load in-
creases, but meets the specified 100µs under the worst
load and VOUT conditions.
Short-Circuit and Thermal Protection
The output current is short-circuit protected. When a
short-circuit fault occurs, the output current is automati-
cally limited and VOUT drops, depending on the actual
short-circuit resistance.
Short-circuit fault or output overload may cause the die
temperature to increase and exceed maximum ratings
due to power dissipation. In such cases, depending
upon the ambient temperature; VIN, load current, and the
junction-to-air thermal resistance (θJA) of the die; the
device may enter thermal shutdown.
When the die temperature exceeds the shutdown limit
temperature, the onboard thermal protection disables
the output until the temperature drops below its hyteresis
value, at which point the output is re-enabled and a new
soft-start sequence occurs as described above.
Thermal Considerations
For best performance, the die temperature and the
power dissipated should be kept at moderate values.
The maximum power dissipated can be evaluated based
on the following relationship:
PD(max)
=
⎧
⎨
⎩
TJ(max) −
Θ JA
TA
⎫
⎬
⎭
(1)
where TJ(max) is the maximum allowable junction tem-
perature of the die and TA is the ambient operating tem-
perature. θJA is dependent on the surrounding PCB lay-
out and can be improved by providing a heat sink of sur-
rounding copper ground.
The addition of backside copper with through-holes, stiff-
eners, and other enhancements can also aid in reducing
θJA. The heat contributed by the dissipation of other de-
vices located nearby must be included in design consid-
erations.
Capacitors Selection
The FAN2564 is stable with a wide range of capacitor
values and sizes.
For loop stability, a 1µF input capacitor or bigger is rec-
ommended. Tolerance, temperature, and voltage coeffi-
cients of the capacitor must be considered to ensure
effective capacitance stays around 1µF or above. There
is no special requirement on its ESR value.
An output capacitor with an effective capacitance be-
tween 1µF and 10µF is required for loop stability. The
ESR value should be within 5 to 100mΩ. 2.2µF or 4.7µF
ceramic capacitors are recommended to ensure stability
over the full temperature, input, and output voltage
range of operation, such as those listed in Table 1.
Table 1. Recommended Capacitors
Capacitance
1μF
2.2μF
2.2μF
4.7μF
4.7μF
Size
0603
0603
0402
0603
0402
Vendor
MURATA
MURATA
MURATA
MURATA
MURATA
Part Number
GRM188R71C105KA120
GRM188R61A225KF340
GRM155R60J225ME15
GRM188C80G475KE19
GRM155R60G475M
© 2007 Fairchild Semiconductor Corporation
FAN2564 • Rev. 1.0.1
9
www.fairchildsemi.com
Share Link: 