NCP3170AGEVB ON Semiconductor, NCP3170AGEVB Datasheet - Page 13

• 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

Over Voltage Protection
buck converter is monitored at the FB pin of the output
power stage. One comparator is placed on the feedback node
to provide over voltage protection. In the event an over
voltage is detected, the high side switch turns off and the low
side switch turns on until the feedback voltage falls below
the OOV threshold. Once the voltage has fallen below the
OOV threshold, switching continues normally as displayed
in Figure 40.
Duty Ratio
a wide output voltage range. The low 8% duty ratio limit will
restrict the PWM operation. For example if the application
is converting to 1.2 V the converter will perform normally
if the input voltage is below 15.5 V. If the input voltage
exceeds 15.5 V while supplying 1.2 V output voltage the
converter can skip pulses during operation. The skipping
pulse operation will result in higher ripple voltage than when
operating in PWM mode. Figure 41 and 42 below shows the
safe operating area for the NCP3170A and B respectively.
While not shown in the safe operating area graph, the output
voltage is capable of increasing to the 93% duty ratio
limitation providing a high output voltage such as 16 V. If
the application requires a high duty ratio such as converting
from 14 V to 10 V the converter will operate normally until
the maximum duty ratio is reached. For example, if the input
voltage were 16 V and the user wanted to produce the
highest possible output voltage at full load, a good rule of
thumb is to use 80% duty ratio. The discrepancy between the
usable duty ratio and the actual duty ratio is due to the
voltage drops in the system, thus leading to a maximum
output voltage of 12.8 V rather than 14.8 V. The actual
achievable output to input voltage ratio is dependent on
layout, component selection, and acceptable output voltage
tolerance.
FB Voltage
1.0 V
0.862 V
0.800 V
0.726 V
Complete
Low Side
Softstart
Upon the completion of soft start, the output voltage of the
The duty ratio can be adjusted from 8% to 92% allowing
Figure 40. Over Voltage Low Side Switch Behavior
Switch
Power
Good
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13
Design Procedure
to collect as much information as possible about the behavior
of the input and output before starting the design.
tool available online under the design tools section of the
NCP3170 product page. The tool allows you to capture your
design point and optimize the performance of your regulator
based on your design criteria.
DESIGN PARAMETERS
Input Voltage (V
Output Voltage (V
Input Ripple Voltage (VCC
Output Ripple Voltage (V
Output Current Rating (I
Operating Frequency (F
When starting the design of a buck regulator, it is important
ON Semiconductor has a Microsoft Excel® based design
Figure 41. NCP3170A Safe Operating Area
Figure 42. NCP3170B Safe Operating Area
Design Parameter
IN
)
OUT
)
SW
OUT
OUTRIPPLE
RIPPLE
)
)
)
)
Example Value
9 V to 16 V
500 kHz
200 mV
20 mV
3.3 V
3 A