NCP1547DR2G ON Semiconductor, NCP1547DR2G Datasheet - Page 10

• 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

current divided by beta of the device. Beta of 60 is used here
to estimate the base current. The Boost pin provides the base
current when the transistor needs to be on. The power
dissipated by the IC due to this current is
where:
and conduction current contribute to the power loss of a
non−ideal switch. The power loss can be quantified as
where:
both high current and voltage during each switch transition.
This regulator has a 30 ns turn−off time and associated
power loss is equal to
not considered here.
ambient temperature, IC power dissipation and thermal
resistance of the package. The equation is shown as follows,
Minimum Load Requirement
required for this regulator due to the pre−driver current
feeding the output. Placing a resistor equal to V
12 mA should prevent any voltage overshoot at light load
conditions. Alternatively, the feedback resistors can be
valued properly to consume 12 mA current.
Input Capacitor
current with an amplitude equal to the load current. This
pulsed current and the ESR of the input capacitors determine
the V
ripple, low ESR is a critical requirement for the input
capacitor selection. The pulsed input current possesses a
significant AC component, which is absorbed by the input
capacitors. The RMS current of the input capacitor can be
calculated using:
The base current of a bipolar transistor is equal to collector
I
When the power switch turns on, the saturation voltage
V
The switching loss occurs when the switch experiences
The turn−on time is much shorter and thus turn−on loss is
The total power dissipated by the IC is sum of all the above
The IC junction temperature can be calculated from the
As pointed out in the previous section, a minimum load is
In a buck converter, the input capacitor witnesses pulsed
S
SAT
W IC + W Q ) W DRV ) W BASE ) W SAT ) W S
= DC switching current.
IN
ripple voltage, which is shown in Figure 13. For V
= saturation voltage of the power switch which is
W DRV + 12 mA
shown in Figure 7.
COMPONENT SELECTION
W S +
W SAT +
T J + W IC
W BASE +
I S
V IN
2
V O
V IN
(V IN * V O )
V O 2
V IN
R qJA ) T A
I S
30 ns
V SAT
60
I S
f S
V O 2
V IN
O
)
divided by
http://onsemi.com
IN
10
where:
with the constant given by Figure 14 at each duty cycle. It is
a common practice to select the input capacitor with an RMS
current rating more than half the maximum load current. If
multiple capacitors are paralleled, the RMS current for each
capacitor should be the total current divided by the number
of capacitors.
design’s constraint and emphasis. The aluminum
electrolytic capacitors are widely available at lowest cost.
Their ESR and ESL (equivalent series inductor) are
relatively high. Multiple capacitors are usually paralleled to
achieve lower ESR. In addition, electrolytic capacitors
usually need to be paralleled with a ceramic capacitor for
filtering high frequency noises. The OS−CON are solid
aluminum electrolytic capacitors, and therefore has a much
lower ESR. Recently, the price of the OS−CON capacitors
has dropped significantly so that it is now feasible to use
Calculated by Multiplying Y Value with Maximum Load
Figure 13. Input Voltage Ripple in a Buck Converter
D = switching duty cycle which is equal to V
I
To calculate the RMS current, multiply the load current
Selecting the capacitor type is determined by each
0.6
0.5
0.3
0.2
0.1
O
0.4
Figure 14. Input Capacitor RMS Current can be
0
= load current.
0
0.2
Current at any Duty Cycle
I RMS + I O D(1 * D)
0.4
DUTY CYCLE
0.6
0.8
O
/V
IN
.
1.0