LMZ14201 how to drive ENpin with aTTL signal ?

[BeO]

Hello

I am stuck since weeks with a nightmare problem

the LMZ14201 from TI  is a voltage converter with a EN Pin able to driven as an on/off I want and need to drive in sequence by using a sequencer LM3880 with 5 V DC

my problem is the TI doc says :

The logic level is 1.18 V
The floating EN Pin Voltage is 6,5 V

so ??

I need a circuit to be able to drive the EN pin in 5 V without to burn the LM3880

can someone will help that will be really great

Regards

BeO

[chris_leyson]

Not exactly clear from the data sheet, but there is an invernal linear regulator which maybe 7V and the EN pin is pulled high by an internal current source. In the data. Figure 32 Evaluation Board Schematic, there is a 5.1V Zenner connected to the EN pin. You could just connect a 4.7V Zenner to the EN pin and that would protest the LM3880 outputs. I like the LMZxx and LMZMxx parts with the integrated inductor, saves a lot of board space.

Chris

[hli]

According to the data sheet: the LMZ14201 turns on then the voltage at EN is higher than 1.18V. The voltage on EN must not be higher than 6.5V (with 7V as maximum allowed voltage). Usually a voltage divider from the input voltage is used to turn on the LMZ14201 when the input voltage is high enough.
When you want to drive with a logic level: use the voltage divider as suggested, and have a NPN transistor in parallel with the bottom resistor (Renb). When you turn on the transistor, it will drive EN low, thus turning it off. If you need an inverted signal (logic high for turning on, you need an additional PNP transistor as logic inverter).

[BeO]

Hello

thanks for yours answers

I have more question

AS the EN pin is floating and I measure a 6.5 V voltage

Ok for the zener diode to protect the LM3880 but :
 if I do NOT ground the EN pin the LMZ start and I do not want that
if I send Voltage the already voltage is 6.5 V

Can HLI confirm his solution is similar to the linked schematic ?

I have located this schematic on the LMZ14203 doc ( similar to the 14201 ) but I do not understand why the output is connected to the EN pin whatever that a negative generator circuit

If I understand what is requested I need a circuit as an inverter to :

a) Ground the floating pin with a resistor so voltage will drop under 1,18 V and the LMZ will not start Vout = 0 V
OR
b) Drive the EN pin by using the LM3880 output voltage of 5 V

some thing which look as an inverter drive by the LM3880 output signal

Regards

BeO

[hli]

EN is an input. Measuring voltage with just a DMM is misleading - the DMM presents no load, and the voltage might be clamped to the internal regulator. Try the same with e.g. a 100kOhm load on that pin.
The data sheet states, on page 10, ' The enable input provides a precise 1.18V band-gap rising threshold to allow direct logic drive...'. So you can drive it directly from the LM3880, nothing bad will happen. (The transistor solution I explained earlier can be used if you want to combine enable with under-voltage-lockout).
AN-2027 is misleading - the level shifter here are used because in an inverting configuration the signal levels are shifted (the AN explains that too).

[BeO]

Hello HLI

Ok for the input pin voltage I will make a measurement with the 100K resistor

Results are :
with 100 K 0.625 V I have no output V out = ) on the LMZ
without I have 6 V V out on the LMZ


for the LM3880 I have try several time to direct drive the EN PIN that work and I burn the LM3880 so
perhaps the input current is over the LM3880 current
perhaps I don't know I don't know and I don't know 

I will try to install a TC4428 and a double N Mosfet to built a inverter switch one way off on a 100 K this way ON

I post results soon

If you have any comments please post them they will be welcome


Regards

BeO

[hli]

Can you show your schematic for the LMZ14201 and the LM3880?

[BeO]

Hello HLI

I will try to test this schematic updated with two Mosfet to drive the EN pin and one p Chanel to put the EN pin to the ground

IN A will ground through a resistor to force LMZ to 0 V output

IN B will power the EN pin to 5 V

and vise versa following flag level ( flag is in 5 V )



Regards

BeO