[SOLVED] [Moved]: max4051 ACPE+ not working above 11,8 v

[njensen]

I'm using a MAX4051 ACPE+ in single supply mode.
V- is connected to ground.

According to datasheet max Vcc is 16 volt.
however around 11,8 volt, it seems that some of the switches not close anymore.

Belov 11.8v Vcc it works like it should.

I see the same thing on 2 pcs.

any ideas why this happens ?

 

[FvM]

Sure you connected all supply pins and INH input? Sufficient logic input level?

 

[njensen]

V+ = 12 volt
V- = GND
INH = GND

Logic high = 3,3 Volt
Logic Low = 0 Volt.

Everything ok when tested at Vcc = 6-11,8 Volt.
Above 11,8 i see input on port 0 also on port 1 e.g.

 

[FvM]

Although the datasheet has no specifications of leakage currents etc. for higher supply voltages than 5.5V, which impedance/leakage do you observe for the open contact? What's the input voltage?

 

[njensen]

open contact impedance is 150-160 kohm.
closed contact impedance is 50-80 ohm (@ Vcc 12v - 6v).

Reason for my problem is the control voltage level.
@ Vcc above 11.8 Volt -> Logic High must be higher than 3.4 volt.
@ Vcc below 11.8 Volt -> Logic High can be 3.3 Volt.

Seems the contacts are in some undefind state when the difference between Vcc and logic control signals are too high.
I cant see that limitation in the data sheet

 

[FvM]

I cant see that limitation in the data sheet

It does mention varying logic thresholds, but misses a clear specification.

It's said the high level is "about 3.1 V" with 12 V supply. This must be apparently read as a typical rather than a required level specification. Parameters without a specification are usually not production tested, so it's difficult to assume a safe level.

That's why I asked about suffcient logic input level in post #2.

 

[bigdogguru]

As Frank indicated, the high level logic threshold values are only specified as typical, increasing gradually as V+ increases.

Reference: , Section: Applications Information - Power-Supply Considerations, Page: 12

Overview

The logic-level thresholds are TTL/CMOS compatible
when V+ is +5V. As V+ rises, the threshold increases
slightly, so when V+ reaches +12V, the threshold is
about 3.1V; above the TTL-guaranteed high-level mini-
mum of 2.8V, but still compatible with CMOS outputs.

Also Note Reference: , Applications Information - Power-Supply Considerations, Page: 12

Single Supply

These devices operate from a single supply between
+3V and +16V when V- is connected to GND. All of the
bipolar precautions must be observed. At room temper-
ature, they actually “work” with a single supply at near
or below +1.7V, although as supply voltage decreases,
switch on-resistance and switching times become very
high.

You did not mention the connections to Pin 8 (Logic GND), your description seems to indicate a common GND between the V+ and the logic section supplies.

Have you verified the the V+ and the logic section supplies of you design share a common GND?