NCP3170AGEVB ON Semiconductor, NCP3170AGEVB Datasheet - Page 17

• Manufacturer Part Number: NCP3170AGEVB
• Description: BOARD EVALUATION NCP3170ADR2G
• Manufacturer: ON Semiconductor
• Series: -r

Specifications of NCP3170AGEVB

• Design Resources: NCP3170 Schematic NCP3170AGEVB BOM
• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Power - Output: -
• Voltage - Output: Adj down to 0.8V
• Current - Output: 3A
• Voltage - Input: 4.5 ~ 18 V
• Regulator Topology: Buck
• Frequency - Switching: 500kHz
• Board Type: Fully Populated
• Utilized Ic / Part: NCP3170
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: NCP3170AGEVBOS

output current. Loss in the input capacitors can be calculated
with the following equation:
CIN
Iin
P
or ceramics should be used. If a tantalum capacitor must be
used, it must be surge protected, otherwise capacitor failure
could occur.
Power MOSFET Dissipation
environment drive power supply design. Once the
dissipation is known, the thermal impedance can be
calculated to prevent the specified maximum junction
temperatures from being exceeded at the highest ambient
temperature.
conduction losses and switching losses. The high−side
MOSFET will display both switching and conduction
losses. The switching losses of the low side MOSFET will
not be calculated as it switches into nearly zero voltage and
the losses are insignificant. However, the body diode in the
low−side MOSFET will suffer diode losses during the
non−overlap time of the gate drivers.
dissipation can be approximated from:
P
P
P
The first term in Equation 21 is the conduction loss of the
high−side MOSFET while it is on.
I
R
P
Using the ra term from Equation 5, I
D
ra
I
I
loss and can be approximated from the following equations.
RMS_HS
OUT
RMS_HS
CIN
COND
D_HS
SW_TOT
COND
DS(ON)_HS
Due to large di/dt through the input capacitors, electrolytic
Power dissipation, package size, and the thermal
Starting with the high−side MOSFET, the power
The second term from Equation 21 is the total switching
RMS
Power dissipation has two primary contributors:
ESR
18 mW + 10 mW
P
CIN
I
P
RMS_HS
+ CIN
= Input capacitance Equivalent Series
= Input capacitance RMS current
= Power loss in the input capacitor
= Conduction losses
= Power losses in the high side MOSFET
= Total switching losses
= RMS current in the high side MOSFET
= On resistance of the high side MOSFET
= Conduction power losses
= Duty ratio
= Ripple current ratio
= Output current
= High side MOSFET RMS current
COND
P
Resistance
D_HS
ESR
+ I
+ I
+ P
RMS_HS
OUT
1.34 A
COND
Iin
RMS
2
) P
2
D
2
SW_TOT
R
RMS
DS(on)_HS
1 )
becomes:
ra
12
2
(eq. 20)
(eq. 21)
(eq. 22)
(eq. 23)
http://onsemi.com
17
P
P
P
P
are the losses associated with turning the high−side
MOSFET on and off and the corresponding overlap in drain
voltage and current.
F
I
P
P
P
t
t
V
side MOSFET, it is important to know the charge
characteristic shown in Figure 44.
IG1
Q
R
R
t
V
V
FALL
RISE
RISE
OUT
DS
RR
SW
SW_TOT
SW
SW
TON
TOFF
P
t
HSPU
G
IN
GD
CL
TH
The first term for total switching losses from Equation 24
When calculating the rise time and fall time of the high
RISE
SW
Vth
Figure 44. High Side MOSFET Total Charge
+ P
+
Q
I
TON
G1
GD
t
RISE
= High side MOSFET drain to source losses
= High side MOSFET reverse recovery
= High side MOSFET switching losses
= High side MOSFET total switching losses
= Switching frequency
= Load current
= High side MOSFET switching losses
= Turn on power losses
= Turn off power losses
= MOSFET fall time
= MOSFET rise time
= Input voltage
= Output current from the high−side gate drive
= MOSFET gate to drain gate charge
= Drive pull up resistance
= MOSFET gate resistance
= MOSFET rise time
= Clamp voltage
= MOSFET gate threshold voltage
+
P
) P
SW_TOT
losses
) t
V
TOFF
CL
FALL
* V
+ P
+
TH
1
2
SW
Q
GD
R
) P
I
OUT
HSPU
DS
) R
) P
V
IN
RR
G
F
SW
(eq. 24)
(eq. 25)
(eq. 26)