Supervisors & Sequencers

two UCD9081 on a single board

Srivatsa Raghunath — Thu, 05 Nov 2009 07:17:46 GMT

Hi,

We're using two UCD9081 devices on a single power management board for sequencing and monitoring different supplies. Let us know how to program both these devices using a single communication. Our GUI is able to talk to only one of these devices at a time. If both are connected, the communication fails

Thanks and regards,

Srivatsa

UCD90120 JTAG and power supply query

Adrian Grindon — Wed, 02 Sep 2009 21:13:44 GMT

We are not using the JTAG interface.

The data sheet implies that I need to put a pull-up on TMS & TDI and a pull-down on Trst_n guess this is for when using the JTAG interface

But Since I am not using this interface, do I need to leave these signals floating ?

I intend on putting a pull-up TDI, TCK,TMS & Trst_n

Can you comment on this

· Do I need them ?

· As a min, what should I pull-up/pull-down

Do I need to put any filtering on the 3V3 supply to the part as it has analog circuits inside, ie a ADC

Thanks

TPS3707-30DGN

gge — Wed, 02 Sep 2009 18:22:11 GMT

Hello

This is a very specific question regarding the DGN package for the 3707. Does the PowerPad under the part connect to the GND signal of the part or what signal is the PowerPad connected to?

TPS3820 transition rate

Dawn Willett — Tue, 26 May 2009 04:31:09 GMT

I would like to have the rise and fall transition rate specification clarified. This item is found in the recommended operating conditions section and is defined as a max of 100ns/V. Can you verify that this is means, in my own words, that the transition time from low to high must be faster than 100ns/V? What will the part do (or not do) if the transition time is slower than 100ns/V?

TPS3808 timing capacitor question

Scot Lester — Thu, 08 Jan 2009 17:54:33 GMT

Question/Problem:

The tps3808 datasheet indicates 1.25msec = 100pF capacitor. However, the equation on page 9 indicates a 1.25msec delay would be a 131pF cap.

Answer:

The minimum time-out specified is 1.25mS and the smallest timing capacitor is specified as 100pF. The electrical characteristics page shows 100pF since this is the extreme in capacitor choices. The time-out using a 100pF still falls within the range shown in the table. The equation is the linear interpretation of the graph shown in Figure 4. You can see in Figure 4 that there is a change in slope of the graph around 1nF. The time versus capacitor value graph becomes slightly non linear for small values of capacitors which is giving the small difference in calculated capacitor values.

TPS3808G09

Stephen Taranovich — Tue, 28 Jul 2009 02:31:24 GMT

In a new design, I’m using a TPS3808 to supervise the voltage of an AA battery. If the voltage is below 0.9 V then the RST pin switches to another battery. In another circuit of the same project, the RST pin simply turns off a switching regulator and allows current from another power supply to supply the circuits powered by the converter just turned off. I selected the version 0.9 because AAs don’t have much more juice left below 0.9 V. In re-reading the datasheet I was not sure about the specs. In page 2 it shows TPS3808G09 with a nominal supply voltage of 0.9 V and a threshold voltage of 0.84 V. What is 0.9 V? Should I use the version G01 and add two resistors so I can have a thresold a bit highr that 0.84? Or should I live it with the 0.9 V version? Why is the threshold voltage so low in the G01 version (0.405 V)? The supervisory chips are powered by a 3 V power supply powered by a lithium battery which cannot be turned off.

TPS3306 and noise

Dweinzierl — Tue, 16 Jun 2009 16:56:13 GMT

I have a customer that is using TPS3306 and they belive noise is coupling into the WDI input.

This is a weakly driven pin that toggles and looks for transitions. How is this pin sampled during transition? Is there any way to calculate a noise margin for WDI?

TPS3820 watchdog question

Scot Lester — Thu, 08 Jan 2009 18:05:36 GMT

Questions/Problem:

When using the TPS3820, what happens if the WDI is active while on both transitions of the WDI input?

Answer:

The RESET is latched low until WDI stops transitioning.

TPS3801 is getting damaged by static

Scot Lester — Thu, 08 Jan 2009 18:02:22 GMT

Question/Problem:

Board is failing static testing. Lifting the MR pin of the TPS3801 from the board makes it pass

Answer:

The MR pin goes to a connector and off board. The connector is exposed to the static during test. Recommend adding small 0.1uF ceramic capacitor between MR and ground at the connector to shunt static away before entering board. Also recommend ferrite bead in series with MR signal.

extending the range of the TPS3808

Scot Lester — Thu, 08 Jan 2009 17:57:35 GMT

Question/Problem:

How can I make my TPS3808 output valid for inputs down to 0V?

Answer:

There is a circuit for doing this in the TL7702A datasheet on page 8.