open drain/collector driver???

[xczms]

drain collector

I'm designing the application platform of the GPRS module MC35i, now I have some problem on the the design of the pin IGH, the electronical description of this pin are as follows:

signal form and level:
RI ≈ 100k, CI ≈ 1nF
VILmax = 0.5V at Imax = -20µA
VOpenmax = 2.3V
ON ~~~|____|~~~ Active Low >100mS

comment:
This signal switches the
mobile ON.
This line must be driven low
by an Open Drain or Open
Collector driver.

could anyone help me with the open drain/collector driver? how to implement it, can you recommend me some chipsets? thank you

 

[pisoiu]

open drain driver

Just use a BSS138 or similar low treshold voltage mosfet. Put drain in the pin of module, source to gnd, and gate to the controller or whatever you use to control that module. A 0-1-0 pulse on the gate will give desired 1-0-1 pulse to start the module. Just comply with the duration of pulse, as specified in the datasheet. Gate is compatible with both 5v and 3v logic levels.

/pisoiu

 

[xczms]

open drain pin

then could i use the transistor like 9013 ?

 

[pisoiu]

how open-drain driver work

then could i use the transistor like 9013 ?

I don't know the parameters of this transistor, but if it is low power and if its treshold voltage (specified in its datasheet) is under the minimum "1" state voltage of your device used to control the module, you can use it. Of course, you can use also a bipolar transistor instead of mosfet, but for this one you have to add a resistor in series with base.

/pisoiu

 

[xczms]

use of open drain

if i use the BSS138, shoud i use the pull-up resistence on the drain pin? and the VOpenmax=2.3v means the high level that ipnut to the module could not be higher than this, right?

 

[pisoiu]

open drain output

if i use the BSS138, shoud i use the pull-up resistence on the drain pin? and the VOpenmax=2.3v means the high level that ipnut to the module could not be higher than this, right?

Usually, that resistor is inside modem. Check the datasheet, and if it says that pin is pulled up, do NOT use an external resistor between drain and vcc. If the pin is not internally pulled up (somehow I doubt this), then put 1kohm between drain and vcc. Vopenmax=2.3 means that the voltage on that pin must be under 2,3v to sense the commnd. Use BSS138 and it will work. Hope it is clear now.

/pisoiu