NCP1251
www.onsemi.com
22
OPP
Vlatch
VCC
au x.
winding
OPP
ROPPL
2.5k
NT C
D2
1N4148
ROPPU
841k
full−latch
Figure 50. The Internal Circuitry Hooked to Pin 3 Can Be Used to Implement Over Temperature Protection (OTP)
Back to our 19 V adapter, we have found that the plateau
voltage on the auxiliary diode was 13 V in nominal
conditions. We have selected an NTC which offers a
resistance of 470 kW at 25°C and drops to 8.8 kW at 110°C.
If our auxiliary winding plateau is 14 V and we consider a
0.6 V forward drop for the diode, then the voltage across the
NTC in fault mode must be:
V
NTC
+ 14 * 3 * 0.6 + 10.4 V
(eq. 17)
Based on the 8.8 kW NTC resistor at 110 °C, the current
through the device must be:
I
NTC
+
10.4
8.8k
[ 1.2 mA
(eq. 18)
As such, the bottom resistor R
OPPL
, can easily be
calculated:
R
OPPL
+
3
1.2m
+ 2.5 kW
(eq. 19)
Now that the pulldown OPP resistor is known, we can
calculate the upper resistor value R
OPPU
to adjust the power
limit at the chosen output power level. Suppose we need a
200 mV decrease from the 0.8 V set point and the on−time
swing on the auxiliary anode is −67.5 V, then we need to drop
over R
OPPU
a voltage of:
V
ROPPU
+ 67.5 * 0.2 + 67.3 V
(eq. 20)
The current flowing in the pulldown resistor R
OPPL
in this
condition will be:
I
ROPPU
+
200m
2.5k
+ 80 mA
(eq. 21)
The R
OPPU
value is therefore easily derived:
R
OPPU
+
67.3
80m
+ 841 kW
(eq. 22)
Combining OVP and OTP
The OTP and Zener−based OVP can be combined
together as illustrated by Figure 51.
NCP1251
www.onsemi.com
23
4
5
1
OPP
Vlatch
10
8
9
VCC
au x.
winding
OPP
ROPPL
2.5k
11
NT C
D2
1N4148
ROPPU
841k
D3
15V
OVP
Figure 51. With the NTC Back in Place, the Circuit Nicely Combines OVP, OTP and OPP on the Same Pin
In nominal V
CC
/ output conditions, when the Zener is not
activated, the NTC can drive the OPP pin and trigger the
adapter in case of an over temperature. During nominal
temperature if the loop is broken, the voltage runaway will
be detected and the controller will shut down the converter.
In case the OPP pin is not used for either OPP or OVP, it
can simply be grounded.
Filtering the Spikes
The auxiliary winding is the seat of spikes that can couple
to the OPP pin via the parasitic capacitances exhibited by the
Zener diode and the series diode. To prevent an adverse
triggering of the Over Voltage Protection circuitry, it is
possible to install a small RC filter before the detection
network. Typical values are those given in Figure 52 and
must be selected to provide the adequate filtering function
without degrading the stand−by power by an excessive
current circulation.
Latched OVP on V
CC
The V
CC
pin is permanently monitored by a comparator.
When the V
CC
exceeds 25.5 V (typical), all pulses are
immediately stopped and the V
CC
falls to the SCR
latched-level around 7 V typical. The controller remains in
this state as long as a sufficient current flows in the SCR, at
least 30 mA. We recommend to put a design margin there,
with a minimum current around 60 mA at the lowest input
line. With the C version, the OVP on V
CC
is autorecovery.
4
5
1
OPP
Vlatch
10
3
9
VCC
aux.
winding
OPP
ROPPL
2.5k
11
NT C
2
D2
1N4148
ROPPU
841k
D3
15V
OVP
R3
220
C1
330pF
ad d ition al fil ter
Figure 52. A Small RC Filter Avoids the Fast Rising Spikes from Reaching the Protection Pin of the NCP1251 in
Presence of Energetic Perturbations Superimposed on the Input Line
NCP1251
www.onsemi.com
24
PACKAGE DIMENSIONS
TSOP−6
CASE 318G−02
ISSUE V
23
456
D
1
e
b
E1
A1
A
0.05
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M, 1994.
2. CONTROLLING DIMENSION: MILLIMETERS.
3. MAXIMUM LEAD THICKNESS INCLUDES LEAD FINISH. MINIMUM
LEAD THICKNESS IS THE MINIMUM THICKNESS OF BASE MATERIAL.
4. DIMENSIONS D AND E1 DO NOT INCLUDE MOLD FLASH,
PROTRUSIONS, OR GATE BURRS. MOLD FLASH, PROTRUSIONS, OR
GATE BURRS SHALL NOT EXCEED 0.15 PER SIDE. DIMENSIONS D
AND E1 ARE DETERMINED AT DATUM H.
5. PIN ONE INDICATOR MUST BE LOCATED IN THE INDICATED ZONE.
c
*For additional information on our Pb−Free strategy and soldering
details, please download the ON Semiconductor Soldering and
Mounting Techniques Reference Manual, SOLDERRM/D.
SOLDERING FOOTPRINT*
DIM
A
MIN NOM MAX
MILLIMETERS
0.90 1.00 1.10
A1 0.01 0.06 0.10
b 0.25 0.38 0.50
c 0.10 0.18 0.26
D 2.90 3.00 3.10
E 2.50 2.75 3.00
e 0.85 0.95 1.05
L 0.20 0.40 0.60
0.25 BSC
L2
0° 10°
1.30 1.50 1.70
E1
E
RECOMMENDED
NOTE 5
L
C
M
H
L2
SEATING
PLANE
GAUGE
PLANE
DETAIL Z
DETAIL Z
0.60
6X
3.20
0.95
6X
0.95
PITCH
DIMENSIONS: MILLIMETERS
M
STYLE 13:
PIN 1. GATE 1
2. SOURCE 2
3. GATE 2
4. DRAIN 2
5. SOURCE 1
6. DRAIN 1
ON Semiconductor and the are registered trademarks of Semiconductor Components Industries, LLC (SCILLC) or its subsidiaries in the United States and/or other countries.
SCILLC owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of SCILLC’s product/patent coverage may be accessed
at www.onsemi.com/site/pdf/Patent−Marking.pdf. SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation
or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and
specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets
and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each
customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended,
or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which
the failure of the SCILLC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or
unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and
expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim
alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable
copyright laws and is not for resale in any manner.
P
UBLICATION ORDERING INFORMATION
N. American Technical Support: 800−282−9855 Toll Free
USA/Canada
Europe, Middle East and Africa Technical Support:
Phone: 421 33 790 2910
Japan Customer Focus Center
Phone: 81−3−5817−1050
NCP1251/D
LITERATURE FULFILLMENT:
Literature Distribution Center for ON Semiconductor
P.O. Box 5163, Denver, Colorado 80217 USA
Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada
Fax: 303−675−2176 or 800−344−3867 Toll Free USA/Canada
Email: orderlit@onsemi.com
ON Semiconductor Website: www.onsemi.com
Order Literature: http://www.onsemi.com/orderlit
For additional information, please contact your loc
al
Sales Representative

NCP1251ASN65T1G

Mfr. #:
Manufacturer:
ON Semiconductor
Description:
Switching Controllers OCP OVP VCC LATCH
Lifecycle:
New from this manufacturer.
Delivery:
DHL FedEx Ups TNT EMS
Payment:
T/T Paypal Visa MoneyGram Western Union