NCP3170AGEVB ON Semiconductor, NCP3170AGEVB Datasheet - Page 18

• 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

IG2
Q
R
R
t
V
V
by both the high−side and low−side MOSFETs, but are
dissipated only in the high−side MOSFET.
C
F
P
V
body diode in the low−side MOSFET is shown as follows:
F
P
Q
V
voltages so switching losses are negligible. The low−side
MOSFET’s power dissipation only consists of conduction
loss due to R
periods.
P
P
P
follows:
I
R
P
FALL
RMS_LS
SW
DS
SW
RR
BODY
COND
D_LS
COND
t
GD
G
HSPD
CL
TH
OSS
IN
RR
IN
DS(ON)_LS
Next, the MOSFET output capacitance losses are caused
Finally, the loss due to the reverse recovery time of the
The low−side MOSFET turns on into small negative
Conduction loss in the low−side MOSFET is described as
FALL
+
Q
I
G2
GD
P
DS(on)
= Output current from the low−side gate
= MOSFET gate to drain gate charge
= MOSFET gate resistance
= Drive pull down resistance
= MOSFET fall time
= Clamp voltage
= MOSFET gate threshold voltage
= MOSFET output capacitance at 0 V
= Switching frequency
= MOSFET drain to source charge losses
= Input voltage
= Switching frequency
= High side MOSFET reverse recovery
= Reverse recovery charge
= Input voltage
= Low side MOSFET body diode losses
= Low side MOSFET conduction losses
= Low side MOSFET losses
= Low−side MOSFET on resistance
= High side MOSFET conduction losses
COND
= RMS current in the low side
+
P
drive
losses
DS
P
P
V
D_LS
RR
and body diode loss during non−overlap
CL
+
+ I
+ Q
* V
1
2
+ P
@ C
RMS_LS
TH
RR
OSS
COND
Q
GD
R
@ V
V
2
HSPD
IN
) P
IN
R
2
BODY
F
DS(on)_LS
) R
@ F
SW
SW
G
(eq. 27)
(eq. 28)
(eq. 29)
(eq. 30)
(eq. 31)
http://onsemi.com
18
D
I
I
ra
The body diode losses can be approximated as:
F
I
NOL
NOLLH
P
V
Compensation Network
To create a stable power supply, the compensation network
around the transconductance amplifier must be used in
conjunction with the PWM generator and the power stage.
Since the power stage design criteria is set by the
application, the compensation network must correct the
overall output to ensure stability. The NCP3170 is a current
mode regulator and as such there exists a voltage loop and
a current loop. The current loop causes the inductor to act
like a current source which governs most of the
characteristics of current mode control. The output inductor
and capacitor of the power stage form a double pole but
because the inductor is treated like a current source in closed
loop, it becomes a single pole system. Since the feedback
loop is controlling the inductor current, it is effectively like
having a current source feeding a capacitor; therefore the
pole is controlled by the load and the output capacitance. A
table of compensation values for 500 kHz and 1 MHz is
provided below for two 22 mF ceramic capacitors. The table
also provides the resistor value for CompCalc at the defined
operating point.
OUT
RMS_LS
OUT
SW
BODY
I
P
FD
RMS_LS
BODY
HL
+ V
+ I
FD
OUT
= Duty ratio
= Load current
= RMS current in the low side
= Ripple current ratio
= Switching frequency
= Low−side MOSFET body diode losses
= Load current
= Dead time between the high−side
= Dead time between the low−side MOSFET
= Body diode forward voltage drop typically
@ I
MOSFET turning off and the low−side
MOSFET turning on, typically 30 ns
turning off and the high−side MOSFET
turning on, typically 30 ns
0.92 V
OUT
@ F
( 1 * D )
SW
@ NOL
1 )
LH
) NOL
ra
12
2
HL
(eq. 32)
(eq. 33)