ST VD5376 Installation and operating instructions

October 2011 Doc ID 018955 Rev 1 1/16
AN3419
Application note
VD5376/VD5377 optical finger navigation testing
1 Introduction
This document gives a non-exhaustive list of tests which may be run on the ST
VD5376/VD5377 optical finger navigation (OFN) devices.
2 Initialization
The initialization setup depends on the customer application (for example, automatic or
manual power mode, direct 1v8 drive or Vtop supply, CPI setting, X/Y direction and so on).
Please refer to the individual application notes for initialization instructions:
● AN3356: Interfacing to the VD5377 optical navigation device (018567)
● AN3217: Interfacing to the VD5376 optical navigation device (017529)
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3 Navigation
This chapter describes the navigation tests that can be performed on the VD5376/VD5477
sensors.
3.1 XY table navigation
Using a mechanical setup gives accurate navigation results of how well the module
navigates at various speeds and over various surfaces.
STMicroelectronics suggested (non finger) surfaces for OFN testing are white card, cotton
and leather glove. Care must be taken when choosing surfaces for XY table testing as the
module surface can be easily scratched with surfaces that are too hard. The images in
Figure 1 to Figure 4 show VD5377 (LOQFP) with standard PC mouse optics on white card.
It demonstrates the accurate navigation achievable with the VD5376/VD5377 sensors.
Figure 1. 2ips Figure 2. 10ips
Figure 3. 20ips Figure 4. 40ips
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In an OFN module setup, high accuracy/high speed is not essential. The images ( Figure 5
and
Figure 6 ) show what is and what is not ( Figure 7 and Figure 8 ) considered acceptable
OFN navigation (plots below were done at 4ips).
Figure 5. OFN good navigation Figure 6. OFN good navigation
Figure 7. OFN bad navigation Figure 8. OFN bad navigation
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The navigation in Figure 5 is oval in shape, but this can be corrected by increasing the X CPI
register setting.
Figure 6 navigation although too small, is circular. The X/Y CPI register settings can both be
increased here to achieve the required CPI value.
Figure 7 shows glitchy navigation while the navigation in Figure 8 drifts, is too small and
does not complete the full circle. These errors cannot be ‘fixed’ by register settings.
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3.2 Finger navigation
Although XY table (mechanical) navigation testing is useful to show the overall accuracy of
the OFN module, the real navigation testing is done by fingers. It is very important to test a
wide range of users/fingers to find the best and worst fingerprints.
The image below shows good finger navigation. The module was tested by manually
swiping a finger across the sensor. One swipe in each direction (
Figure 9 ).
Figure 9. Manual finger swipes - good navigation
1
2
3
4
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Figure 10. Manual finger swipes - bad navigation
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Figure 11. Manual Swipes - bad (jittery) navigation
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Typical current consumption AN3419
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4 Typical current consumption
Ta bl e 1 shows typical current consumption on a VD5377.
The figures for the VD5377 Idle and Sleep modes are given at their default settings.
Ta bl e 2 shows typical current consumption on a VD5376.
Automatic power management mode should not be used with VD5376 in applications with
more than one device on the I2C bus.
Table 1. VD5377 typical current consumption
Mode Max exposure
Run fast 10mA
Run medium 6mA
Run Slow 3.5mA
Idle 1 350uA
Idle 2 100uA
Sleep 50uA
Powerdown <1uA
Table 2. VD5376 typical current consumption
Mode Max exposure
Run fast 9mA
Run medium 5mA
Run Slow 3mA
Powerdown 40uA
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5 Images
This chapter describes tests that can be performed on the VD5376/VD5377 sensors that
involve using the sensors to capture images.
5.1 External
It can be useful to take images with an IR camera to show that the navigation surface is
being illuminated effectively.
Figure 12. Example external image
5.2 Internal
There are two methods of getting images from the VD5376/VD5377 sensors. Both are
described in separate application notes.
●Image download over I2C:
–
AN3415: VD5376 image download over I2C (018944)
–
AN3414: VD5377 image download over I2C (018941)
●Fast image streaming:
–
AN3417: VD5376 OFN high speed imaging system (018949)
–
AN3418: VD5377 OFN high speed imaging system (018952)
Image download over I2C is very slow on the VD5376 (0.5fps), this is because of the auto
increment I2C read function. This can be disabled on the VD5377, enabling a much faster
image download. Customers can create their own application or use the ST one, along with
the ST OFN test board (PCB1389C) and ST7 firmware. Although this does require the
customer to create their own adapter board for the OFN (see
Figure 13 for size/connector
details).
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Figure 13. PCB1389 OFN adapter board
Fast Image Streaming - images are captured in real time. Although four extra test pins are
required on the OFN module for this test mode. See application notes AN3417 and AN3418
for more details.
In both
Figure 14 and Figure 15 , the image download application shows Features, MEP and
exposure.
Figure 14. VD5377 ST image download application (1x optics)
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