NCP1443T ON Semiconductor, NCP1443T Datasheet - Page 17

• Manufacturer Part Number: NCP1443T
• Description: IC REG 4A 280KHZ NEG TO220-7
• Manufacturer: ON Semiconductor
• Type: Step-Up (Boost), Inverting, Flyback, Forward Converter, Sepicr

Specifications of NCP1443T

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: Adjustable
• Current - Output: 4A
• Frequency - Switching: 280kHz
• Voltage - Input: 2.7 ~ 30 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: TO-220-7 (Straight Leads)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Other names: NCP1443TOS

generation of heat in the junctions at the surface of the chip.
This heat is transferred to the surface of the IC package, but
a thermal gradient exists due to the resistive properties of the
package molding compound. The magnitude of the thermal
gradient is expressed in manufacturers’ data sheets as q
or junction−to−ambient thermal resistance. The on−chip
junction temperature can be calculated if q
temperature near the surface of the IC, and the on−chip
power dissipation are known.
where:
be found on page 19 of the datasheet, under “Package
Thermal Data.” Note that this value is different for every
package style and every manufacturer. For the NCP144X,
q
the copper pad to which the IC is mounted.
whether the NCP144X can be used in an application is
settled. If T
allowable junction temperature, the NCP144X is not
suitable for that application.
possible means of reducing the junction temperature.
Perhaps another converter topology could be selected to
reduce the switch current. Increasing the airflow across the
JA
Power dissipation in a semiconductor device results in the
T
T
P
q
For ON Semiconductor components, the value for q
Once the designer has calculated T
If T
A
D
JA
J
varies between 10−50°C/W, depending upon the size of
= IC or FET junction temperature (°C);
= ambient temperature (°C);
= power dissipated by part in question (W);
= junction−to−ambient thermal resistance (°C/W).
J
approaches 150°C, the designer should consider
J
exceeds 150°C, the absolute maximum
T J + T A )(P D q JA )
J
, the question of
JA
, the air
http://onsemi.com
JA
can
JA
,
17
surface of the chip might be considered to reduce T
copper “landing pad” can be connected to ground −
designers are referred to ON Semiconductor applications
note SR006 for more information on properly sizing a
copper area.
Circuit Layout Guidelines
important for proper operation. Rapidly switching currents
combined with trace inductance generates voltage
transitions that can cause problems. Therefore the following
guidelines should be followed in the layout.
In any switching power supply, circuit layout is very
1. In boost circuits, high AC current circulates within the
2. Separate the low current signal grounds from the
3. Locate the voltage feedback resistors as near the IC as
loop composed of the diode, output capacitor, and
on−chip power transistor. The length of associated
traces and leads should be kept as short as possible. In
the flyback circuit, high AC current loops exist on both
sides of the transformer. On the primary side, the loop
consists of the input capacitor, transformer, and
on−chip power transistor, while the transformer,
rectifier diodes, and output capacitors form another
loop on the secondary side. Just as in the boost circuit,
all traces and leads containing large AC currents
should be kept short.
power grounds. Use single point grounding or ground
plane construction for the best results.
possible to keep the sensitive feedback wiring short.
Connect feedback resistors to the low current analog
ground.
A
. A