The Ultra-Low Power buck, TPS62737, and input output signal selection levels

CHAMKHI HAITHEM

Other Parts Discussed in Thread: TPS62737, TPS62736, TS5A9411

Hi,

I'm using the TPS62737, Ultra-Low Power Buck Converter, to convert a lithuim coin cell rechargeable battery to an 2.5V to feed the circuits on my board. Here's the datasheet : www.ti.com/.../slvsbo4c.pdf

the input voltage is variable, starting from 4.2V when the coin cell is fully charged to 2.75V when the battery is discharged. here's the battery datasheet : www.ti.com/.../slvsbo4c.pdf

the desired output voltage is 2.5v to feed the microcontrollers and other circuit and the VIN_OK threshold is about 3.35v. for that i use the 3 resistors methode using these values R1 = 4.7M, R2 = 1.6M, R3 = 6.7M. using

So i have 2 question :
1/ to put the TPS62737 into the normal mode ,meaning Buck mode ON and VIN_OK enabled, i have to put the EN1 pin to the Gnd and the EN2 to the Vdd. but i don't know which vdd should i use. the VDD of the VIN (battery voltage) or the output voltage 2.5V ??

2/ the VIN_OK output signal which indicate to the microcontroller that the input voltage is OK. i don't know if i have to use an external Pull-Up resitor and connect it to the Vout, or the VIN_OK has an internal Pull-Up resistor and in this case i have to use an external transistor to match the voltage level? if that correct which transistor should i use to minimize the power consumption ?

here's a picture of the circuit :

Thanks for the help,

over 10 years ago

0 Lubomir over 10 years ago

TI__Intellectual 2415 points

Dear Mr. Haithem,

please find my answer below:

I recommend to connect EN2 to input voltage like it is in evaluation module for TPS62736:
VIN_OK is pulled to VIN pin. It is not necessary to use pull up resistor. The logic high level of the signal VIN_OK is equal to input voltage. It is necessary to use BJT or another component to match the voltage level (output voltage) for microcontroller. I believe that you can achieve lower consumption of generating OK signal for microcontroller with analog switch for example: TS5A941: http://www.ti.com/lit/ds/symlink/ts5a9411.pdf comparing to BJT solution.

Best regards

Lubomir Fenic

0 CHAMKHI HAITHEM over 10 years ago in reply to Lubomir

Prodigy 110 points

Thx1. so the EN1 & 1 input and the Vout_OK are matched to the Vin output as i understand

2. is that correct the schema below using the TS5A9411 circuit.

Thx,

0 Lubomir over 10 years ago in reply to CHAMKHI HAITHEM

TI__Intellectual 2415 points

Dear Mr. Haithem,

TPS62737 doesn't have Vout_OK pin. VIN_OK is pulled up to VIN pin.
Yes, schema for TS5A9411 is correct.

Best regards

Lubomir Fenic

0 CHAMKHI HAITHEM over 10 years ago in reply to CHAMKHI HAITHEM

Prodigy 110 points

Hi, thx for the quick answer,

i wan to know if i can also use the TS5A9411 to drive a buzzer ??

0 Lubomir over 10 years ago in reply to CHAMKHI HAITHEM

TI__Intellectual 2415 points

Dear Mr. Haithem,

I think that you can use it but be careful with the current require for driving buzzer. You can find ON resistance in D/S of TS5A9411 and calculate maximum power losses. Thermal impedance of the package DCK is 259°C/W.

Best regards

Lubomir Fenic

0 Chancey Kelley over 8 years ago

Prodigy 30 points

I see that you are trying to use the VIN_OK pin as a digital indicator. Instead of using it in that manner, why not use it as an analog input via a voltage divider? That way you can monitor the LIR2450's voltage directly? Using resistors in the MegOHM range would keep discharge to a minimum and allow you to control the state of your micro (deep sleep, warning indicator, etc...).

As per the datasheet (pg 7, "EN1 and EN2") "VIH Voltage for EN High setting. Relative to VIN -> VIN – 0.2".

Good Luck.

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The Ultra-Low Power buck, TPS62737, and input output signal selection levels