NCP1547DR2G ON Semiconductor, NCP1547DR2G Datasheet - Page 7

• Manufacturer Part Number: NCP1547DR2G
• Description: IC REG BUCK 1.5A 340KHZ 8-SOIC
• Manufacturer: ON Semiconductor
• Type: Step-Down (Buck)r

Specifications of NCP1547DR2G

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.5 ~ 24 V
• Current - Output: 1.5A
• Frequency - Switching: 340kHz
• Voltage - Input: 4.5 ~ 40 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

frequency. The SYNC pin equivalent input circuit is shown
in Figure 5.
switch to start a new switching cycle, as shown in Figure 6.
There is approximately 0.5 ms delay between the rising edge
of the sync pulse and rising edge of the V
sync threshold is TTL logic compatible, and duty cycle of
the sync pulses can vary from 10% to 90%. The frequency
foldback feature is disabled during the sync mode.
102.5
97.5
92.5
An external clock signal can sync the NCP1547 to a higher
The rising edge of the sync pulse turns on the power
Synchronized to an External 443 kHz Pulse Signal
100
95
90
Figure 4. Oscillator Frequency Versus Junction
−40
Sync
Figure 6. A NCP1547 Buck Regulator is
−20
V
T
to 20V
Z
J
0
±33%
, JUNCTION TEMPERATURE (°C)
10k
= 11V
20
Temperature
Figure 5.
40
50k
±33%
60
80
50k
±33%
SW
100
pin voltage. The
120
GND
140
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7
Power Switch and Current Limit
connected to the V
When the switch turns on, the V
V
the V
when the power switch turns off, and the inductor current is
commutated to the catch diode. Due to the presence of high
pulsed current, the traces connecting the V
and diode should be kept as short as possible to minimize the
noise and radiation. For the same reason, the input capacitor
should be placed close to the V
diode.
on the switching current, as shown in Figure 7.
to protect the power switch and external components. When
the peak of the switching current reaches the Current Limit,
the power switch turns off after the Current Limit Delay. The
switch will not turn on until the next switching cycle. The
current limit threshold is independent of switching duty
cycle. The maximum load current, given by the following
formula under continuous conduction mode, is less than the
Current Limit due to the ripple current.
where:
subharmonic oscillation may cause low frequency
Figure 7. The Saturation Voltage of the Power Switch
IN
The collector of the built−in NPN power switch is
The saturation voltage of the power switch is dependent
The NCP1547 contains pulse−by−pulse current limiting
f
I
V
V
L = inductor value.
When the regulator runs under current limit, the
0.7
0.6
0.5
0.4
0.3
0.2
0.1
S
LIM
O
IN
minus switch Saturation Voltage. In the buck regulator,
0
= switching frequency,
SW
= output voltage,
0
= input voltage,
= current limit threshold,
Increases with the Conducting Current
voltage swings to one diode drop below ground
I O(MAX) + I LIM *
IN
SWITCHING CURRENT (A)
0.5
pin, and the emitter to the V
IN
V O (V IN * V O )
SW
2(L)(V IN )(f s )
pin and the anode of the
voltage is equal to the
1.0
SW
pin, inductor
SW
1.5
pin.