Microchip Technology MCP651, Руководство пользователя

Страница: 23 / 39

MCP651 INPUT OFFSET
EVALUATION BOARD
USER’S GUIDE
©
2009 Microchip Technology Inc. DS51834A-page 19
Chapter 3. Possible Modifications
3.1 INTRODUCTION
This chapter shows how to modify the MCP651 Input Offset Evaluation Board to
measure other single op amps from Microchip Technology Inc. Items discussed in this
chapter include:
• Range of Parts Supported by the MCP651 Input Offset Evaluation Board
• Changes to Accommodate Other DUTs
3.2 RANGE OF PARTS SUPPORTED BY MCP651 INPUT OFFSET EVALUATION
BOARD
Only op amps that fall within a certain performance range are supported by the
MCP651 Input Offset Evaluation Board.
3.2.1 Input Offset Voltage
In order to keep op amps U3 and U4 operating normally, the DUT’s V
OS
must be:
EQUATION 3-1:
More accurate op amps need higher gain for good resolution. Table 3-1 shows what
V
OS
specs can be supported for different voltmeter resolutions and amplifier gains.
TABLE 3-1: LOWER LIMIT ON V
OS
RANGE (NOTE 1)
Voltmeter Resolution
(mV)
G
A
G
M
(V/V)
max (V
OS
)
≥
(±µV)
1 mV 201 (low gain) 500
1998 (high gain) 50
0.1 mV 201 (low gain) 50
1998 (high gain) 5 (Note 2)
Note 1: These results assume a minimum measurement resolution of 1% of the V
OS
range.
2: The DUT needs to be soldered to the PCB when the maximum V
OST
is less than
±50 µV, or so. Inserting a PDIP-8 part into a 8-pin socket creates a contact potential
(error) of the order of ±1 µV. Also, 1/f noise needs to be low.
V
OS
12.4 mV, Low Gain
± <
V
OS
1.25 mV, High Gain
±
<
Where:
Low Gain = 201 V/V
High Gain = 1998 V/V