LMZ14201 how to drive ENpin with aTTL signal ? - Page 1
Forum section: electronics / beginners

author: BeO
author_rank: Contributor
timestamp: July 03, 2018, 05:27:16 pm
content: HelloI am stuck since weeks with a nightmare problemthe 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 DCmy problem is the TI doc says :The logic level is 1.18 VThe floating EN Pin Voltage is 6,5 Vso??I need a circuit to be able to drive the EN pin in 5 V without to burn the LM3880can someone will help that will be really greatRegardsBeO

author: chris_leyson
author_rank: Super Contributor
timestamp: July 03, 2018, 05:43:39 pm
content: 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

author: hli
author_rank: Frequent Contributor
timestamp: July 04, 2018, 08:49:11 am
content: 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).

author: BeO
author_rank: Contributor
timestamp: July 04, 2018, 10:06:48 am
content: Hellothanks for yours answersI have more questionAS the EN pin is floating and I measure a 6.5 V voltageOk 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 thatif I send Voltage the already voltage is 6.5 VCan HLI confirm his solution is similar to the linked schematic ?I have located this schematic on the LMZ14203 doc ( similar to the 14201 ) butI do not understand whythe output is connected to the EN pin whatever that a negative generator circuitIf 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 VORb) Drive the EN pin by using the LM3880 output voltage of 5 Vsome thing which look as an inverter drive by the LM3880 output signalRegardsBeO

author: hli
author_rank: Frequent Contributor
timestamp: July 04, 2018, 09:56:59 pm
content: 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).

author: BeO
author_rank: Contributor
timestamp: July 05, 2018, 08:40:18 am
content: Hello HLIOk for the input pin voltage I will make a measurement with the 100K resistorResults are :with 100 K 0.625 V I have no output V out = ) on the LMZwithout I have 6 V V out on the LMZfor the LM3880 I have try several time to direct drive the EN PIN that work and I burn the LM3880 soperhaps the input current is over the LM3880 currentperhaps I don't know I don't know and I don't knowI 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 ONI post results soonIf you have any comments please post them they will be welcomeRegardsBeO

author: hli
author_rank: Frequent Contributor
timestamp: July 05, 2018, 09:01:33 am
content: Can you show your schematic for the LMZ14201 and the LM3880?

author: BeO
author_rank: Contributor
timestamp: July 06, 2018, 12:06:55 pm
content: Hello HLII 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 groundIN A will ground through a resistor to force LMZ to 0 V outputIN B will power the EN pin to 5 Vand vise versa following flag level ( flag is in 5 V )RegardsBeO