User's Manual Part 1

MC75 Hardware Interface Description
Strictly confidential / Draft
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MC75_V00.190a Page 24 of 91 15.02.2005
3.2 Power Up / Power Down Scenarios
In general, be sure not to turn on MC75 while it is beyond the safety limits of voltage and
temperature stated in Chapter 5. MC75 would immediately switch off after having started and
detected these inappropriate conditions. In extreme cases this can cause permanent
damage to the module.
3.2.1 Turn on MC75
MC75 can be started in a variety of ways as described in the following sections:
• Hardware driven start-up by IGT line: starts normal operating state (see Section 3.2.1.1)
• Software controlled reset by AT+CFUN command: starts normal operating state (see
Section 3.2.1.3)
• Hardware driven start-up by VCHARGE line: starts charging algorithm and charge-only
mode (see Section 3.2.1.2)
• Wake-up from Power-down mode by using RTC interrupt: starts Alarm mode
3.2.1.1 Turn on MC75 Using Ignition Line IGT
When the MC75 module is in Power-down mode, it can be started to normal operation by
driving the IGT (ignition) line to ground. This must be accomplished with an open
drain/collector driver to avoid current flowing into this pin.
The module will start up when both of the following two conditions are met:
• The supply voltage applied at BATT+ must be in the operating range.
• The IGT line needs to be driven low for at least 300ms.
Considering different strategies of host application design the figures below show two
approaches to meet this requirement: The example in Figure 5 assumes that IGT is activated
after BATT+ has already been applied. The example in Figure 6 assumes that IGT is held
low before BATT+ is switched on. In either case, to power on the module, ensure that low
state of IGT takes at least 300ms from the moment the voltage at BATT+ is available.