ICL7139CPL 데이터 시트보기 (PDF) - Intersil
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ICL7139CPL Datasheet PDF : 13 Pages
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ICL7139, ICL7149
Printed Circuit Board Layout Considerations
Particular attention must be paid to rollover performance,
leakages, and guarding when designing the PCB for a
ICL7139 and ICL7149 based multimeter.
9 10 11 12 13 14 15
FIGURE 15. PC BOARD LAYOUT
Rollover Performance, Leakages, and Guarding
Because the ICL7139 and ICL7149 system measures very
low currents, it is essential that the PCB have low leakage.
Boards should be properly cleaned after soldering. Areas of
particular importance are: 1) The INT V/Ω and INT l Pins; 2)
The Triple Point; 3) The RDElNT and the CAZ pins.
The conversion scheme used by the ICL7139 and ICL7149
changes the common mode voltage on the integrator and
the capacitors CAZ and ClNT during a positive deintegrate
cycle. Stray capacitance to ground is charged when this
occurs, removing some of the charge on ClNT and causing
rollover error. Rollover error increases about 1 count for each
picofarad of capacitance between CAZ or the Triple Point
and ground, and is seen as a zero offset for positive volt-
ages. Rollover error is not seen as gain error.
The rollover error causes the width of the +0 count to be
larger than normal. The ICL7139 and ICL7149 will thus read
zero until several hundred microvolts are applied in the posi-
tive direction. The ICL7139 and ICL7149 will read -1 when
approximately -100µV is applied.
The rollover error can be minimized by guarding the Triple
Point and CAZ nodes with a trace connected to the ClNT pin,
(see Figure 15) which is driven by the output of the integra-
tor. Guarding these nodes with the output of the integrator
reduces the stray capacitance to ground, which minimizes
the charge error on ClNT and CAZ. If possible, the guarding
should be used on both sides of the PC board.
Stray Pickup
While the ICL7139 and ICL7149 have excellent rejection of
line frequency noise and pickup in the DC ranges, any stray
coupling will affect the AC reading. Generally, the analog cir-
cuitry should be as close as possible to the ICL7139 and
ICL7149. The analog circuitry should be removed or
shielded from any 120V AC power inputs, and any AC
sources such as LCD drive waveforms. Keeping the analog
circuit section close to the ICL7139 and ICL7149 will also
help keep the area free of any loops, thus reducing magneti-
cally coupled interference coming from power transformers,
or other sources.
All Intersil semiconductor products are manufactured, assembled and tested under ISO9000 quality systems certification.
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design and/or specifications at any time without
notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate
and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which
may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see web site http://www.intersil.com
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