User's Manual

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Note d’étude / Technical document : URD1– OTL
5665.3 – 003 / 72238 Edition 01
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To avoid any power up issue, here are the rules:

Avoid any over voltage on the buses lines connected to the module.

When the module is off, do not apply any voltage on lines connected to the module.
The over voltage can be avoided by using the same power domain voltage.
 Avoid 5V or 3.3V systems straight connection to 2.8V HiLoNC V2 lines.
 Use level adaptors when the power domain requires it.
When the module is off:
 Powers off the buses lines of the main system that are connected to the module, this avoid any flow back
current (re-injection) and of course help a lot to improve and control the power consumption. This last issue is
important as in off mode there is not control of the current inside the module and can results in a loss of current
by leakage through the I/Os of the module.
4.14.4 EXAMPLE OF A CURRENT RE-INJECTION ON U.A.R.T.
Current re-injection appears when the module is off or not powered and I/Os connected to the module still
powered. Example: UART bus powered from the DTE side before the module is powered. This can result in a
bad starting behaviour.

To avoid current re-injection, simply do not supply the lines connected to the module before the module
switches on. Power up the module first using the POK_IN Line then open the UART lines for the DTE side and
all necessary I/O, this will avoid leakage of current improving the power consumption and avoid any possible
deadlock issue during the power up process.
Figure 32: Digital Pad-out clamp diode

All the digital pads have this structure a current re-injection by supplying the lines with a non compliant
voltage range must be avoided. (From -0.4V up to 2.8V+0.4V)

Reverse currents over 15mA will damage the chip. Avoid this issue. Keep the connected line voltage
between 0 and 2.8V.

For an interface with a CMOS 3.3V system or TTL 5V system, use level adapters powered by 2 supplies:
a 2.8V from a LDO IC which is enabled by VGPIO signal and the other external required voltage 3.3V or 5V.

If a Level shifter is used or a RS232 adapter, use the VGPIO signal as the enable signal to avoid any
current re-injection before the module start.
Power supply domain
Pad_X
IN Buffer
OUT Buffer
Vd = 0.4V
Vd = 0.4V
I max = 15mA
I max = 15mA
Clamp
Diode
Clamp
Diode