NCP1547DR2G ON Semiconductor, NCP1547DR2G Datasheet - Page 11

• 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

them for some low cost designs. Electrolytic capacitors are
physically large, and not used in applications where the size,
and especially height is the major concern.
Since the ceramic capacitor has low ESR and ESL, a single
ceramic capacitor can be adequate for both low frequency
and high frequency noises. The disadvantage of ceramic
capacitors are their high cost. Solid tantalum capacitors can
have low ESR and small size. However, the reliability of the
tantalum capacitor is always a concern in the application
where the capacitor may experience surge current.
Output Capacitor
capacitor are not as critical as those on the input capacitor.
The current to the output capacitor comes from the inductor
and thus is triangular. In most applications, this makes the
RMS ripple current not an issue in selecting output
capacitors.
Figure 15. The Output Voltage Ripple Using Two 10 mF
Ceramic capacitors are now available in values over 10 mF.
In a buck converter, the requirements on the output
Figure 17. The Output Voltage Ripple Using
Ceramic Capacitors in Parallel
One 100 mF OS−CON
http://onsemi.com
11
caused by ripple current flowing through ESR, and a square
wave due to ESL. Capacitive reactance is assumed to be
small compared to ESR and ESL. The peak to peak ripple
current of the inductor is:
to the product of I
across the ESL is proportional to the di/dt of the output
capacitor. It is realized that the di/dt of the output capacitor
is the same as the di/dt of the inductor current. Therefore,
when the switch turns on, the di/dt is equal to (V
and it becomes V
ripple voltage induced by ESL can then be derived from
V
RIPPLE(ESL)
The output ripple voltage is the sum of a triangular wave
V
The total output ripple is the sum of the V
Figure 18. The Output Voltage Ripple Using
V RIPPLE(ESL) + ESL(
Figure 16. The Output Voltage Ripple Using One
RIPPLE(ESR)
One 100 mF Tantalum Capacitor
.
100 mF POSCAP Capacitor
, the output ripple due to the ESR, is equal
I P * P +
O
/L when the switch turns off. The total
P−P
VO
and ESR. The voltage developed
L
) ) ESL(
V O (V IN * V O )
(V IN )(L)(f S )
V IN * V O
L
RIPPLE(ESR)
) + ESL(
IN
− V
V IN
L
O
)/L,
)
and