NCP5173MNR2 ON Semiconductor, NCP5173MNR2 Datasheet - Page 15

• Manufacturer Part Number: NCP5173MNR2
• Description: IC PWM BUCK BST FLYBCK INV 8DIP
• Manufacturer: ON Semiconductor
• Type: Step-Up (Boost), Inverting, Flyback, Forward Converter, Sepic, PWM - Current Moder

Specifications of NCP5173MNR2

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: Adjustable
• Current - Output: 1.5A
• Frequency - Switching: 560kHz
• Voltage - Input: 2.7 ~ 30 V
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: *
• Package / Case: 8-TDFN Exposed Pad
• Voltage - Supply: 2.7 V ~ 30 V
• Frequency-max: 1MHz
• Duty Cycle: 90%
• Pwm Type: Current Mode
• Buck: Yes
• Boost: Yes
• Flyback: Yes
• Inverting: Yes
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: NCP5173MNR2OS

linear regulator, requires a small amount of power even
when the switch is turned off. The specifications section of
this datasheet reveals that the typical operating current, I
due to this circuitry is 5.5 mA. Additional guidance can be
found in the graph of operating current vs. temperature. This
graph shows that IQ is strongly dependent on input voltage,
V
drive current must be factored in as well. This current is
drawn from the V
current. The base drive current is listed in the specifications
as DI
designer will find additional guidance in the graphs. With
that information, the designer can calculate:
where:
boost converter,
source of on−chip power loss. V
collector−emitter voltage of the internal NPN transistor
when it is driven into saturation by its base drive current. The
value for V
or from the graphs, as “Switch Saturation Voltage.” Thus,
Finally, the total on−chip power losses are:
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
P BIAS + V IN I Q
P DRIVER + V IN I SW
I SW(AVG) ^ I LOAD
I SW(AVG) ^
D ^
P SAT ^ V (CE)SAT I SW
P D + P BIAS )P DRIVER )P SAT
IN
The internal control circuitry, including the oscillator and
Since the onboard switch is an NPN transistor, the base
I
D = the duty cycle or percentage of switch on−time.
I
In a flyback converter,
The switch saturation voltage, V
Power dissipation in a semiconductor device results in the
SW
SW
, and temperature. Then:
V OUT )
CC
= the current through the switch;
and D are dependent on the type of converter. In a
/DI
V OUT
SW
(CE)SAT
, or switch transconductance. As before, the
V OUT I LOAD
N S
N P
V IN
IN
D ^
V IN
can be obtained from the specifications
pin, in addition to the control circuitry
V OUT * V IN
D
DI SW
I CC
V OUT
D
Efficiency
Efficiency
1
D
(CE)SAT
1
(CE)SAT
, is the last major
is the
http://onsemi.com
JA
Q
,
,
15
junction temperature can be calculated if q
temperature near the surface of the IC, and the on−chip
power dissipation are known.
where:
whether the IC can be used in an application is settled. If T
exceeds 150°C, the absolute maximum allowable junction
temperature, the NCP5173 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
surface of the chip might be considered to reduce T
copper “landing pad” can be connected to the ground pin −
Designers are referred to ON Semiconductor Application
Note AND8036/D 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.
T J + T A )(P D q JA )
T
T
P
q
For the NCP5173, q
Once the designer has calculated T
If T
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
A
D
JA
J
= IC or FET junction temperature (°C);
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.
= 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
JA
= 35°C/W.
J
, the question of
JA
, the air
A
. A
J