NCP345EVB ON Semiconductor, NCP345EVB Datasheet

NCP345EVB

Manufacturer Part Number

NCP345EVB

Description

EVAL BOARD FOR NCP345

Manufacturer

ON Semiconductor

Datasheets

1.NCP345SNT1.pdf (8 pages)

2.NCP345EVB.pdf (1 pages)

3.NCP345EVB.pdf (4 pages)

Specifications of NCP345EVB

Design Resources

NCP345 Demo Board BOM NCP345EVB Gerber Files NCP345/6 EVB Schematic

Main Purpose

Overvoltage Protection

Embedded

Utilized Ic / Part

NCP345

Lead Free Status / RoHS Status

Lead free / RoHS Compliant

Secondary Attributes

Primary Attributes

Lead Free Status / Rohs Status

Lead free / RoHS Compliant

For Use With/related Products

NCP345

Other names

NCP345EVBOS

Current page: 1 of 4
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AND8203/D

Simple Input Adapter

Reverse Voltage Protection

Prepared by: Jim Hill

ON Semiconductor

regulated voltages to power various subsystems. The

number of voltage rails has risen as new generations of

processors, memory, etc. have been introduced with lower

voltage requirements driven by deep sub−micron CMOS

processes. One of the consequences of these new process

technologies is that the absolute maximum ratings have also

been lowered, therefore designers are forced to employ

protection circuitry to protect sensitive I/O’s from transient

and steady−state overvoltage and reverse voltage

conditions.

result in overvoltage events that can damage sensitive

electronic components within the product. Also, due to the

proliferation of portable products within the home and

office, a risk exists that the user may reach for the wrong

adapter which could have a reversed polarity. The challenge

of the product designer is to improve the robustness of the

design and avoid situations where the product can be

damaged.

any reverse current into the adapter. However, Schottky

diodes have a forward voltage drop, V

depending on the forward current, I

have maximum voltage of 4.2 V. Finally, adapter voltages

March, 2005 − Rev. 0

Modern electronic systems require a host of different

Failures and faults in the adapter may, and usually do,

A series Schottky will clamp the reverse voltage and block

−

(Optional)

Figure 1. NCP345/6 Circuit with Reverse Input Voltage Protection

(Optional)

. Next, Li−Ion batteries

GND

, from 0.3−0.5 V

−

ref

Logic

Microprocessor port

CNTRL

are falling due to the standardization of single−cell Li−Ion

as a portable power source, and by lowering the adapter

output voltage, the output power is reduced and thus the size

and cost of the adapter. So in many cases, there is not enough

voltage headroom to support the addition of a Schottky to

provide reverse clamping.

transients up to 30 V and steady state overvoltage faults of

25 V while allowing normal operation for low voltage

adapter inputs. The NCP345/6 senses an overvoltage

condition and quickly disconnects the input voltage supply

from the load by turning off Q1. The NCP345 senses

overvoltage events greater than 6.85 V and the NCP346

comes in two versions which detect overvoltage events

greater than 4.45 and 5.5 V respectively. An optional

resistor divider may be used to adjust the detection threshold

to a higher value as well. Transistor Q2 protects the circuit

from a reverse input voltage condition. For a correct, or

positive, input voltage (V

rises above the body diode voltage of the transistor. The

body diode polarity allows the source to pull up to the input

voltage which turns on the transistor and shorts out the

diode. For a reversed V

is not allowed to turn on.

NCP345/6

The circuit in Figure 1 protects its output from input

Driver

FET

OUT

APPLICATION NOTE

, since the gate is grounded, the FET

http://onsemi.com

), the transistor turns on once V

Publication Order Number:

AND8203/D

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NCP345EVB Summary of contents

Page 1

... AND8203/D Simple Input Adapter Reverse Voltage Protection Prepared by: Jim Hill ON Semiconductor Modern electronic systems require a host of different regulated voltages to power various subsystems. The number of voltage rails has risen as new generations of processors, memory, etc. have been introduced with lower voltage requirements driven by deep sub−micron CMOS processes ...

Page 2

Table 2 shows a variety of MOSFETs that one could choose to implement this solution. The drain−source breakdown voltage (V ) and the gate−source DSmax Table 1. Small, Surface−Mount FETs Part Number V DSmax NTHS4111P 30 NTGS4111P 30 NTJS4151P 20 ...

Page 3

Notes http://onsemi.com 3 ...

Page 4

... Fax: 480−829−7709 or 800−344−3867 Toll Free USA/Canada Email: orderlit@onsemi.com N. American Technical Support: 800−282−9855 Toll Free USA/Canada Japan: ON Semiconductor, Japan Customer Focus Center 2−9−1 Kamimeguro, Meguro−ku, Tokyo, Japan 153−0051 Phone: 81−3−5773−3850 http://onsemi.com 4 ON Semiconductor Website: http://onsemi ...

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