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NCV47700 Datasheet(PDF) 10 Page - ON Semiconductor

No. de Pieza. NCV47700
Descripción  5 V to 20 V Adjustable Low Dropout Regulator with Adjustable Current Limit
Descarga  12 Pages
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Fabricante  ONSEMI [ON Semiconductor]
Página de inicio  http://www.onsemi.com
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NCV47700 Datasheet(HTML) 10 Page - ON Semiconductor

 
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NCV47700
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10
The output voltage is calculated from the following formula.
Ignoring the bias current into the ADJ pin:
Vout + VREF1 1 )
R1
R2
(eq. 2)
Use R2 < 50 kW to avoid significant voltage output errors
due to ADJ bias current.
Designers should consider the tolerance of R1 and R2 during
the design phase.
Setting the Output Current Limit
The output current limit can be set between 10 mA and
350 mA by external resistor RCSO (see Figure 1). Capacitor
CCSO of 1 mF in parallel with RCSO is required for stability
of current limit control circuitry (see Figure 1).
VCSO + Iout RCSO
1
100
(eq. 3)
ILIM +
100
1
2.55
RCSO
(eq. 4)
RCSO +
100
1
2.55
ILIM
(eq. 5)
Where
RCSO
− current limit setting resistor
VCSO
− voltage at CSO pin proportional to Iout
ILIM
− current limit value
Iout
− output current actual value
CSO pin provides information about output current actual
value. The CSO voltage is proportional to output current
according to Equation 3.
Once output current reaches its limit value (ILIM) set by
external resistor RCSO than voltage at CSO pin is typically
2.55 V. Calculations of ILIM or RCSO values can be done
using equations Equation 4 and Equation 5, respectively.
Thermal Considerations
As power in the NCV47700 increases, it might become
necessary to provide some thermal relief. The maximum
power dissipation supported by the device is dependent
upon board design and layout. Mounting pad configuration
on the PCB, the board material, and the ambient temperature
affect the rate of junction temperature rise for the part. When
the NCV47700 has good thermal conductivity through the
PCB, the junction temperature will be relatively low with
high power applications. The maximum dissipation the
NCV47700 can handle is given by:
PD(MAX) +
TJ(MAX) * TA
RqJA
(eq. 6)
Since TJ is not recommended to exceed 150°C, then the
NCV47700 soldered on 645 mm2, 1 oz copper area, FR4
can dissipate up to 1.8 W (SOIC−8 EP) or 1 W (SOIC−8) and
up to 4.3 W (SOIC−8 EP) or 1.6 W (SOIC−8) for 4 layers
PCB (all layers are 1 oz) when the ambient temperature (TA)
is 25
°C. See Figure 18 for RthJA versus PCB area. The power
dissipated by the NCV47700 can be calculated from the
following equations:
PD + Vin Iq@Iout ) Iout Vin * Vout
(eq. 7)
or
Vin(MAX) [
PD(MAX) ) Vout Iout
Iout ) Iq
(eq. 8)
Hints
Vin and GND printed circuit board traces should be as
wide as possible. When the impedance of these traces is
high, there is a chance to pick up noise or cause the regulator
to malfunction. Place external components, especially the
output capacitor, as close as possible to the NCV47700 and
make traces as short as possible.
Figure 18. Thermal Resistance vs. PCB Copper Area
40
60
80
100
120
140
160
180
0
100
200
300
400
500
600
700
COPPER HEAT SPREADER AREA (mm2)
SO−8 EP 4 layers PCB
SO−8 EP single layer PCB
20
200
220
SO−8 single layer PCB
1 oz
2 oz
1 oz
2 oz
1 oz
2 oz
1 oz 2 oz
SO−8 4 layers PCB
ORDERING INFORMATION
Device
Output Voltage
Marking
Package
Shipping
NCV47700PDAJR2G
Adjustable
47700
SOIC−8 EP
(Pb−Free)
2500 / Tape & Reel
NCV47700DAJR2G
Adjustable
47700
SOIC−8
(Pb−Free)
2500 / Tape & Reel
†For information on tape and reel specifications,including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.


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