Non-Isolated DC/DC Forum - Recent Threads

TPS61220 package and pinout

Antoine Palaysi — Fri, 24 May 2013 14:52:12 GMT

Hello everyone,

I just bought the TPS61220DCKT boost converter and I wish to test it. Unfortunatly, I can't find the component pinout. The package top view given by the datasheet do not match with the component i have. The datasheet show a little square on the upper left of the component, when all I have on mine is a horizontal ligne crossing.
The package drawing is visible, so i'm sure this is the right component.

The datasheet is here:

http://www.ti.com/lit/ds/symlink/tps61220.pdf

I hope someone can help me,

Antoine

LM3481 INPUT/OUTPUT Capacitor Selection

takishin — Fri, 24 May 2013 11:14:48 GMT

Our customer has some questions about LM3481.
I'm posting the questions for a customer:

++++++++++++++++++++++++++++++++++++++++++++++

(1)

The datasheet(SNVS346E) says ;
"The input capacitor should be capable of handling the rms current. Although the input capacitor is not as critical
in a SEPIC application, low values can cause impedance interactions. Therefore a good quality capacitor should
be chosen in the range of 100uF to 200uF."

How to decide the capacitance in the range of 100uF to 200uF with LM3481?
(Are there calculating formulas for the capacitance of INPUT/OUTPUT capacitors ?)

(2)

The datasheet(SNVS346E) says "Use capacitors with low ESR and ESL".

Specifically, what ohm is better for low ESR and ESL of the capacitor with LM3481?

++++++++++++++++++++++++++++++++++++++++++++++

thanks in advance.

TPS63001 accuracy

KENSUKE YAITA — Fri, 24 May 2013 02:37:26 GMT

Hi,

I have a question about TPS63001(3.3V) output voltage accuracy.

I saw link below and I understand TPS63001 accuracy is MAX 1%(3.267V-3.333V).

http://e2e.ti.com/support/power_management/non-isolated_dcdc/w/design_notes/tps63001-accuracy.aspx

But my customer verify the ouput voltage 3.376V(disable Power Save Mode) on his test board.

Is voltage accuracy of TPS63001 evaluated by ATE?

It isn't written in datasheet, So I concerned about that.

Regards,

Yaita

TPS54383, 24V->12V burns at no load

Stephan Wille — Fri, 24 May 2013 09:42:32 GMT

Hello,

we are developing a DC DC converter with the TPS54383. In first test runs the circuit worked fine but lately a TPS54383 burned down two times at no load. We have used a boot capacitor of 33nF and a boot strap resistor of 3Ohm.

If we measure the SW1 voltage we have voltage peeks up to 31V with a Duration of approx. 10ns. In the datasheet the max. voltage for SW1 is rated with 31V. So first the question if this voltage (supplied by the boot capacitor ?) is a Problem for the TPS as it's rated up to Vcc max. 28V ?

What could be a possible problem that we have killed the TPS ? We are using a 47uH coil.

Best regards,

Stephan Wille

LM5010A NC-Pins

Stefan Dreyer — Fri, 24 May 2013 08:27:50 GMT

Hi guys,

I wanna use the LM5010A in my application. Concerning the NC pins the datasheet states:

NC - No internal connection. Can be connected to ground plane to
improve heat dissipation.

In the evaluation module, I saw that you connected the pins with their neighboring pins, which massively simplifies the layouting.

Just to confirm: Is it safe to do so?

Cheers,

Stefan

LM5119

eli — Wed, 22 May 2013 11:39:57 GMT

Got the below question:

I'm using TI UCC27211 driver to drive the buck MOSFETs and I want to make sure I'm connecting the LM5119 correctly. In order to drive the high side input of the UCC27211, I connected the LM5119 SW pin to GND and the VCC pin directly to HB pin (without a diode).

TPS53219/ TPS53219A

Dmitri Yablokov — Tue, 17 Jan 2012 15:20:19 GMT

Hi, team,

What is the difference between TPS53219 and TPS53219A just released?

Best regards,

Dmitri.

TPS61251 problem in 100% duty cycle mode

Motty Fattal — Tue, 14 May 2013 06:14:57 GMT

i have an application powered from lithium battery (3.6v).

The TPS61251 is programed to 3.2v output.

The logic bhaind this design is when the battery new & in warm wheter the 100% duty cycle mode is selected, and the output will track the input.

In cold wheter or old battery the TPS61251 will boost the output to 3.2v.

I have a noise problem (like switching noise) only in the 100% duty cycle mode, the boost mode is o.k.

Any idea ??????????????

I have a current limit resistor of about 0.5A, but the current is far less & there is no problem in the boost mode (supuse to draw more current).

I prefer the TPS61251 on the TPS61252 becuase is snoze mode for very low output current.

LM27402, LM22678, TPS63700 - ψJT

S.Satoshi — Tue, 21 May 2013 15:49:45 GMT

Hi,

Now our customer evaluating following devices and they hope to know the ψJT to calculate θJT. Can you prepare it for these devices or let me know example value from similar package?

LM27402SQX/NOPB

LM22678TJ-5.0/NOPB

TPS63700DRCR

Best Regards,

Sonoki

TPS5120 prebias start-up

K.Hamamoto — Wed, 22 May 2013 14:32:19 GMT

Does this part have a prebias start-up function?

Shut down of LM3481 not working

Rob vreden — Fri, 17 May 2013 15:09:31 GMT

Hello TI support,

Can you please help me with the LM3481? I still have not solved an isue I have using the Sut down pin.

The stepup used is to boost 12Volt to 24 Volts. All works well. But when I connect the SD pin to 5 Volts, it will not shut down. what happens is that the output Voltages drops from 24 Volts to 11Volts. in the datasheet it is stated that it will go into sleepmode and draws only a few uA.

I use a 68k normally to gnd. I have put in series with the 68k resistor a 10k to plus 5Volt. when I connect this 78K to plus 5 Volt, it lowers to 11Volts.

when I connect the junction 10k-|-68k to the gnd, it delivers 24Volts again.

I also connected the pin directly( via 10k) to 5Volts, but the outcome is the same( 11Volts)

I can share the schematics and pcb layout if needed. but the schematic is standard and derived from Webench.

kind regards,

Rob van VReden

TPS6122x Minimum ON time

Kevin Braswell — Wed, 22 May 2013 17:11:56 GMT

I'm looking at using TPS61222 in a customer's application. Here are the relevant specs of the design.

- Vin=4V

- Vout=5V

- L = 4.7uH

- Iload = 100mA(max), no minimum specified

The customer is understandably concerned about possible noise and they wanted to know the following.

1. What is the switching frequency.

2. What is the minimum on time.

For item #1, I referenced the datasheet AND SwitcherPro. Both indicated a switching frequency of ~900kHz (based on the inductor). The switching frequency does not change notably over load.

For item #2, the datasheet provides NO guidance. SwitcherPro indicates the "duty cycle" drops with the load current (down to ~7% at 10mA). Since the frequency stays the same, there seems to be 2 ways to interpret this duty cycle results

- One interpretation is that the switcher is only active ~7% of the time (the remaining ~93% of the time the switcher is inactive and the load current is supplied from the output capacitance). When the switcher is active, it presumably runs at ~50% duty cycle, so the minimum on time would be (0.5 / 900kHz = ~0.6us), which would not vary over load.

- Another interpretation is that the switcher is practically always active, with the ON pulses getting narrower (reducing the duty cycle). This duty cycle value indicates the on time is shortest at light loads and can be as low as ~75ns at 10mA (and even shorter at less load). This does not seem to be a feasible interpretation as it implies some amazingly short on times, especially as the load drops below 10mA.

I'd just like confirmation which is the correct interpretation of "duty cycle" and what the minimum ON time is.

Thanks!

TPS55340 not switching; input equals output

Armand Feynrich — Tue, 09 Apr 2013 03:58:20 GMT

I'm attempting to prototype a boosting power supply based on the TPS55340. The issue I'm having is that the whole system seems to have a voltage gain of one: the output voltage is not boosted beyond the input, i.e. the inductor is behaving like short. This leads me to believe that the chip is not switching as it should.

I've tried ramping up the feedback network to force greater gain in the error amplifier, but no change. I've moved caps around, swapped cap dielectrics and chemistries, used higher precision resistors, triple checked connections, and swapped ICs. All attempts had no effect.

I'm beginning to think that either I'm just missing something simple, or this chip simply an't be prototyped without fabricating a PCB first.

The circuit is built on a prototyping board (not a PCB). I'm aware that the layout of switching converters is quite important, and I've done my best to follow what I know to be best practices (components close to pins, small traces, etc.) however I do not know if this is enough. In the past I've been able to build buck-boost converters on a proto-board before ordering a PCB, but these were not TI chips.

I did the design calculations by hand, but they match almost exactly with the component values I get from the excel design helper:

So: can anybody think of what I might be doing wrong, based on my symptoms?

TPS40210 Current Output Too Low / Early Overcurrent Shutdown

Thomas Schmit — Tue, 30 Apr 2013 21:57:35 GMT

Hello,

The circuit takes a 24 volt input and bumps it up to a nominal 48 volts. The designed output current using SwitcherPro Desktop is 4.2 amps. The schematic is inserted below as an image. However, when the output is connected to a test load, the switching stops. If the load is gradually ramped down, I can draw at most about 2.1 amps before it goes into overcurrent mode. Typically, it stops switching at about 1.4 amps.

The voltage on the Isens pin reaches a maximum of 40 mV, at which point it stops switching. During the overcurrent situation, the voltage on this pin falls to roughly 1 mV and stays there until retry. I attempted to short this pin to ground in order to see if I could draw more current. While shorted to ground, the controller stopped switching at less than 0.8 amps.

While there is no load, the FB pin is at 701 mV. As I apply a load, this voltage increases until reaching a maximum of about 737 mV when the controller stops switching.

These values were measured with a Keithley 197A DMM. The voltage on the Isens pin as measured by a scope is very noisy. I increased the capacitance from 180 pF to 1000 pF, which reduced some of the noise on the signal but did not improve the situation.

Any help would be greatly appreciated.

TPS5450 Ringing PH(Switching Node)

Fernando Santiago — Tue, 21 May 2013 20:25:17 GMT

I have some problems with the device TPS5450.

Attached follows the design report generated with SwitcherPro. We mounted exactly the same circuit designed on this report but we found some problems on the functional and high current tests.

Connecting a 5A load on the output, a noise appear on my DC signal (regulated to 5V), the source of this noise is the PH(Switching node) pin.

Of course, I have low ESR output Capacitors and the lowest loop between the Vin, PH and GND. I prefered to use little components to decrease the parasite inductance on the circuit.

In my tests, the Ringing on PH pin is very elevated when the input voltage is low (around 9V to 12V).

So, the diode recommended by the Switcher PRO have a slight high capacitance .I tested the circuit with a lower capacitance diode and results were best. The ringing level and the propagation time were decreased.

The screens show these tests.

The First and the second pictures show the signal on the PH pin using the diode STPS5L60S(Capacitance ~ 280pf) similar to the recommended diode. The test conditions are: Vin = 8,5V and Load Output ~2,5A.

The third and fourth pictures show the signal on the PH pin using the diode STPS340S(Capacitance ~100pf) and the same test conditions.

My guess about the source of the problem is the diode.

Anyone had any problem similar to this?

(Please visit the site to view this file)

What if PH pin volatge under specification of TPS5432?

Hedy Hung — Wed, 22 May 2013 09:21:04 GMT

Dears,

What damage will be caused if PH voltage is under spec's minimum voltage? There are two application of TPS5432 on my board, one is 5V transfer 3.3V, another is 5V transfer 1.2V. Since I measured PH pin voltage (corss IC's pin3) is -2.6V and -2.52V, but PH voltage of specification is -0.6V. I'm afraid any risk been caused! Please help and advise me, thanks.

TPS63030 unstable

eli — Wed, 22 May 2013 08:12:45 GMT

When we check it the TPS63030EVM-417 as is (the power-saving mode disabled) we can see that:

At No Load – Switching frequency = 800khz.

Up to 0.13A – Switching frequency unstable.

More than 0.13A – Switching frequency = 2.4Mhz.

No additional Cin/Cout help.

Our load will be 0.05A (Switching frequency unstable).

Is it normal operation?

TPS40304 Soft Start Feature

Adam Elias — Thu, 02 May 2013 02:51:31 GMT

Hello,

I'm designing a power supply to step down a voltage from 4V to 15V down to 3.3V. I have the design in the lab working well, but I have an issue with the soft-start circuit where I believe the FSS resistor connected from EN/SS to BP is biasing the soft-start capacitor as well as the intentional 10µA current source. This in turn is cutting my desired soft start time by at least 3, hence triggering the over-current upon start-up.

Can someone verify that I am correct in this thinking? With a 0.33µF capacitor on the EN/SS I expect ~20ms of soft start. When the FSS 267k resistor is attached from EN/SS to BP this turns into ~7ms of soft-start.

If this is the case, nothing is stated in the datasheet. I would expect somewhere in the datasheet to state, "Hey, if you use the FSS resistor use this equation for your soft start calculation" I don't know the equation since I just simulated in SPICE instead to obtain my above example numbers.

Lastly, the block diagram does not do a good job in showing the LDRV and HDRV over current sensing. If I read the data sheet correctly this is a measurement of the VDS voltage on the upper and lower MOSFET during a switch cycle. I'm taking it that is a measurement from VDD? - SW for the high side and SW - GND for the low side. The block diagram doesn't show this well, and I can't imagine it being terribly accurate since VDD could be pretty far from the high side MOSFET. The low side MOSFET should be a little a more accurate.

Thanks,

Adam

TPS61221 with LDO TPS78230 or TPS72730 in a Row

Thomas Schneider1 — Tue, 21 May 2013 19:08:27 GMT

Hi,

since I posted regarding the usage of the TPS61221 and his inrush current limiting, I come in trouble with this attached configuration.

We would like to get stabilized 3V from a primary lithium cell (2-3.65V) by using the TPS61221 with a 20R in front due to IS, getting 3.3V out of the converter and supplied then the LDO TPS78230 or TPS72730 to get the 3V.

With both LDO behind the DC/DC, we hang up in the start process of the DCDC under several load conditions around 100Ohm(30mA).

We found out, that supplying directly with the DC/DC works fine, but the ripple is too high for our application. So we investigated the LDO more and found out, that the EN treshold of the LDO (min.0.9V) is below the level of 1.8V, which is needed to become the normal current operation mode for the DC/DC. Thats results in hung up of the DC/DC in this mode and an increased current(feed trough) in the system without starting.

If we enabled the LDO by hand later after starting process of the DC/DC, everything works fine.

So, our questions are, do you have any reference designs for that or what can we do, to get this running. We tried already some delay on the enable pin of the LDO and a voltage divider, but these are no reliable solutions for us. Do we the first who needs such a configuration??

Many thanks in foreward!

5V, 0.5A output from LM5010

Hw47343 — Tue, 21 May 2013 14:04:24 GMT

Hi,

Have anybody used LM5010MH for 5V and 0.5A output. I am using this IC for my application (Input is from 20V to 75V) but it blows off.

Kind regards,

Varindra

Power Sequencing with multiple TPS62130 and TPS53319

Peter Watson — Tue, 21 May 2013 12:07:36 GMT

Hello,

The controller I am using on my board requires that the five differnet voltages powering it power up one after the other.

First, the +3.3V generated by a TPS62130

then +2.5V generated by another TPS62130

then +1.2V generated by a third TPS62130

then +0.8V generated by a TPS53319

and last +0.67V generated by a second TPS53319

To meet this requirement, for each voltage regulator I connected the "Power Good" pin to the "Enable" pin of the following voltage regulator. (SEE ATTACHED SCHEMATIC FOR DETAILS)

But now I am facing the problem that the PG pins of the TPS62130s indicate "Power Good" even though the corresponding voltage regulator isn't even enabled yet by its preceding voltage regulator. Why is "Power Good" (high-impedance) indicated by the device if the output voltage is still 0V?

How can I solve this problem and make sure that one power powers up after the other?

Thank you very much for your help!

LM3671-ADJ output voltage limitation

Go — Tue, 21 May 2013 03:39:36 GMT

Hi,

I'd like to ask about the output voltage limitation for LM3671-ADJ (up to 3.3V).

Where does the limitaion come from?

Thanks,

TPS51716 / Example of DDR3 solution

S.Satoshi — Mon, 20 May 2013 16:02:33 GMT

Hi,

Now our customer evaluate TPS51716 to drive three pieces of DDR3 memory in parallel. They are understanding that the required current is depend on the kind of DDR3 device but they would like to know the some example or reference which drive the multiple DDR3 memories in parallel. Do you have some example or reference design?

Best Regards,

Sonoki / Disty in Japan

LM3224 thermal resistance

Scott Kerstein — Thu, 16 May 2013 23:15:06 GMT

Hello,

I’m looking for the thermal resistance from junction to ambient (θja) of the LM3224. In the datasheet, it talks about using θja to calculate power, but it’s not called out anywhere. I need the info quickly because the customer is looking to add a load onto this power supply and I need to know whether it can handle it.

Thank you in advance,

Scott

TPS40400 Vdd=3.3V BP6=? (i.e. What are the MOSFET driver voltages?)

Christopher George — Sat, 18 May 2013 21:08:03 GMT

Hello,

We are trying to determine the applicability/efficiency of the TPS40400 when Vin and Vdd are both tied to a 3.3V voltage rail. The data sheet (page 16) says BP6 is internally generated with a linear regulator, no on-board charge pump capability is mentioned. Will the BP6 voltage (i.e. Hdrv/Ldrv ) equal the Vdd voltage (3.3V) minus the linear regulator drop out voltage? In other words, when Vdd=3.3V what is the BP6 voltage?

Also, is the datasheet's Figure 23 correct? It shows increased efficiency with increased Vin?

Thanks,

Chris