MC13201 Technical Data, Rev. 1.3,
20 Freescale Semiconductor
8.3 Low Power Considerations
• Program and use the modem IO pins properly for low power operation
— All unused modem GPIOx signals must be used one of 2 ways:
– If the Off mode is to be used as a long term low power mode, unused GPIO should be tied
to ground. The default GPIO mode is an input and there will be no conflict.
– If only Hibernate and/or Doze modes are used as long term low power modes, the GPIO
should programmed as outputs in the low state.
— When modem GPIO are used as outputs:
– Pullup resistors should be provided (can be provided by the MCU IO pin if tied to the MCU)
if the modem Off condition is to be used as a long term low power mode.
– During Hibernate and/or Doze modes, the GPIO will retain its programmed output state.
— If the modem GPIO is used as an input, the GPIO should be driven by its source during all low
power modes or a pullup resistor should be provided.
— Digital outputs IRQ, MISO, and CLKO:
– MISO - is always an output. During Hibernate, Doze, and active modes, the default
condition is for the MISO output to go to tristate when CE is de-asserted, and this can cause
a problem with the MCU because one of its inputs can float. Program Control_B Register
07, Bit 11, miso_hiz_en = 0 so that MISO is driven low when CE is de-asserted. As a result,
MISO will not float when Doze or Hibernate Mode is enabled.
–IRQ - is an open drain output (OD) and should always have a pullup resistor (typically
provided by the MCU IO). IRQ acts as the interrupt request output.
NOTE
It is good practice to have the IRQ interrupt input to the MCU disabled
during the hardware reset to the modem. After releasing the modem
hardware reset, the interrupt request input to the MCU can then be enabled
to await the IRQ
that signifies the modem is ready and in Idle mode; this can
prevent a possible extraneous false interrupt request.
– CLKO - is always an output. During Hibernate CLKO retains its output state, but does not
toggle. During Doze, CLKO may toggle depending on whether it is being used.
• If the MCU is also going to be used in low power modes, be sure that all unused IO are programmed
properly for low power operation (typically best case is as outputs in the low state). The MC13201
is commonly used with the Freescale MC9S08GT/GB 8-bit devices. For these MCUs:
— Use only STOP2 and STOP3 modes (not STOP1) with these devices where the GPIO states are
retained. The MCU must retain control of the MC13201 IO during low power operation.
— As stated above all unused GPIO should be programmed as outputs low for lowest power and
no floating inputs.
3
A wider frequency stability may be acceptable if application uses trimming at production final test.
4
A wider aging tolerance may be acceptable if application uses trimming at production final test.
5
Higher ESR may be acceptable with lower load capacitance.
6
Lower load capacitance can allow higher ESR and is better for low temperature operation in Doze mode.
