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PDF NCP1215A Data sheet ( Hoja de datos )
| Número de pieza | NCP1215A | |
| Descripción | Low Cost Variable OFF Time Switched Mode Power Supply Controller | |
| Fabricantes | ON Semiconductor | |
| Logotipo |  |
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NCP1215A
Low Cost Variable OFF
Time Switched Mode Power
Supply Controller
The NCP1215A is a controller for low power off−line flyback
Switched Mode Power Supplies (SMPS) featuring low size, weight
and cost constraints together with a good low standby power
performance. The operating principle uses switching frequency
reduction at light load by increasing the OFF Time. Also, when OFF
Time expands, the peak current is gradually reduced down to
approximately 1/4 of the maximum peak current to prevent from
exciting the transformer mechanical resonances. The risk of acoustic
noise is thus greatly diminished while keeping good standby power
performance.
A low power internal supply block also ensures very low current
consumption at startup without hampering the standby power
performance.
A special primary current sensing technique minimizes the impact
of SMPS switching on control IC operation. The choice of peak
voltage across the current sense resistor allows dissipation to be
further reduced. The negative current sensing technique offers
advantages over a traditional approach by avoiding the voltage drop
incurred by traditional MOSFET source sensing. Thus, the IC drive
capability is greatly improved.
Finally, the bulk input ripple ensures a natural frequency dithering
which smooths the EMI signature.
Features
• Variable OFF Time Control Method
• Very Low Current Consumption at Startup
• Natural Frequency Dithering for Improved EMI Signature
• Current Mode Control Operation
• Peak Current Compression Reduces Transformer Noise
• Programmable Current Sense Resistor Peak Voltage
• Undervoltage Lockout
• Pb−Free Packages are Available
Typical Applications
• Auxiliary Power Supply
• Standby Power Supply
• AC−DC Adapter
• Off−line Battery Charger
© Semiconductor Components Industries, LLC, 2005
September, 2005 − Rev. 2
1
http://onsemi.com
MARKING
DIAGRAM
8
1
SOIC−8
D SUFFIX
CASE 751
8
1215A
ALYW
G
1
TSOP−6
6
6
(SOT23−6, SC59−6)
SN SUFFIX
FACAYW G
G
1
CASE 318G
1
FAC = Specific Device Code
A = Assembly Location
L = Wafer Lot
Y = Year
W = Work Week
G = Pb−Free Package
(Note: Microdot may be in either location)
PIN CONNECTIONS
SOIC−8
FB 1
8 NC
CT 2
7 NC
CS 3
GND 4
6 VCC
5 Gate
(Top View)
TSOP−6
CS 1
6 Gate
GND 2
CT 3
5 VCC
4 FB
(Top View)
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 3 of this data sheet.
Publication Order Number:
NCP1215A/D
1 page  
NCP1215A
TYPICAL CHARACTERISTICS
11.6 8.8
11.5 8.7
11.4 8.6
11.3 8.5
11.2 8.4
11.1 8.3
11.0
−25
0 25 50 75 100
TJ, JUNCTION TEMPERATURE (°C)
125
Figure 3. Vstartup Threshold vs. Junction
Temperature
8.2
−25
0 25 50 75 100
TJ, JUNCTION TEMPERATURE (°C)
Figure 4. VUVLO Threshold vs. Junction
Temperature
125
0.990
0.985
0.980
0.975
0.970
0.965
0.960
−25
0 25 50 75 100
TJ, JUNCTION TEMPERATURE (°C)
125
Figure 5. Operating Current Consumption vs.
Junction Temperature
1.20
1.18
1.16
1.14
1.12
1.10
1.08
1.06
1.04
1.02
1.00
−25
0 25 50 75 100
TJ, JUNCTION TEMPERATURE (°C)
Figure 6. Offset Voltage vs. Junction
Temperature
125
49.0
48.5
48.0
47.5
47.0
46.5
46.0
45.5
−25
0 25 50 75 100
TJ, JUNCTION TEMPERATURE (°C)
125
Figure 7. Current Sense Source Current vs.
Junction Temperature
65
60
55
50
45
40
35
30
−25
0 25 50 75 100
TJ, JUNCTION TEMPERATURE (°C)
Figure 8. Current Sense Threshold vs.
Junction Temperature
125
http://onsemi.com
5
5 Page 
NCP1215A
The EF16 core for transformer was selected. It has
cross−section area Ae = 20.1 mm2. The N67 magnetic
allows to use maximum operating flux density
Bmax = 0.28 Tesla.
The number of turns of the primary winding is:
np
+
Lp · Ippk
B max · Ae
+
4.14 ·
0.28
10−3 · 0.2047
· 20.1 · 10−6
+
150
turns
(eq. 20)
The AL factor of the transformer’s core can be calculated:
AL
+
Lp
(np)2
+
4.14 · 10−3
(150)2
·
+
184
nH
(eq. 21)
For an adapter output voltage of 6.5 V, the number of turns
of the secondary winding can be calculated accounting
Schottky diode for output rectifier as follows:
ns
+
(Vs
) Vfwd)(1 * d
d max · Vbulk−
max)np
min
(eq. 22)
+
(6.5
)
0.7)(1 * 0.5)150
0.5 · 127
+
8.5
+
9
turns
The number of turns for auxiliary winding can be
calculated similarly:
ns
+
(Vs
) Vfwd)(1 * d
d max · Vbulk−
max)np
min
(eq. 23)
+
(12
)
1)(1 * 0.5)150
0.5 · 127
+
15.35
+
15
turns
The peak primary current is known from initial
calculations. The current sense method allows choosing the
voltage drop across the current sense resistor. Let’s use a
value of 0.5 V. The value of the current sense resistor can
then be evaluated as follows:
RCS
+
VCS
Ippk
+
0.5
0.2047
+
2.442
W
+
2.7
W
(eq. 24)
The voltage drop across the sense resistor needs to be
recalculated:
VCS + RCS · Ippk + 2.7 · 0.2047 + 0.553 V (eq. 25)
Using the above results the value of the shift resistor is:
Rshift
+
VCS
ICS
+
0.553
50 · 10−6
+
11.06
kW
+
11
kW
(eq.
26)
The value of timing capacitor for the off time control has
to be calculated for minimum bulk capacitor voltage since
at these conditions the converter should be able to deliver
specified maximum output power. The value of the timing
capacitor is then given by the following equation:
CT
+
1
fsw
*
1.2
Lp · Ippk
Vbulk− min
· 106
(eq. 27)
+
75
1
· 103
* 4.14 · 10*3 ·
127
0.12 · 106
0.2047
+
55.5
pF
+
56
pF
The value of the startup resistor for startup time of 200 ms
and VCC capacitor of 200 nF is following:
Rstartup
+
CVcc
Vbulk− min
Vstartup
tstartup
)
ICC−start
MAX
+
200
·
10−9
127
12
0.2
)
10
·
10−6
+ 5.77 MW + 5.6 MW
(eq. 28)
The result of all the calculations is the application
schematic depicted in Figure 21.
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