MC75i Hardware Interface Description
3.2 Power Supply
71
MC75i_HD_v01.100a
Page 25 of 122
2009-08-13
Confidential / Released
3.2
Power Supply
MC75i needs to be connected to a power supply at the board-to-board connector (5 lines each
BATT+ and GND).
The power supply of MC75i has to be a single voltage source at BATT+. It must be able to pro-
vide the peak current during the uplink transmission.
All the key functions for supplying power to the device are handled by the power management
section of the analog controller. This IC provides the following features:
•
Stabilizes
the supply voltages for the GSM baseband using low drop linear voltage regula-
tors and a DC-DC step down switching regulator.
•
Switches the module's power voltages for the power-up and -down procedures.
•
Delivers, across the VEXT line, a regulated voltage for an external application. This voltage
is not available in Power-down mode.
•
SIM switch to provide SIM power supply.
3.2.1
Minimizing Power Losses
When designing the power supply for your application please pay specific attention to power
losses. Ensure that the input voltage V
BATT+
never drops below 3.2V on the MC75i board, not
even in a transmit burst where current consumption can rise to typical peaks of 2A. It should
be noted that MC75i switches off when exceeding these limits. Any voltage drops that may oc-
cur in a transmit burst should not exceed 400mV.
The measurement network monitors outburst and inburst values. The drop is the difference of
both values. The maximum drop (Dmax) since the last start of the module will be saved. In IDLE
and SLEEP mode, the module switches off if the minimum battery voltage (V
batt
min) is reached.
Example:
V
I
min = 3.2V
Dmax = 0.4V
V
batt
min = V
I
min + Dmax
V
batt
min = 3.2V + 0.4V = 3.6V
The best approach to reducing voltage drops is to use a board-to-board connection as recom-
mended, and a low impedance power source. The resistance of the power supply lines on the
host board and of a battery pack should also be considered.
Note:
If the application design requires an adapter cable between both board-to-board connectors,
use a flex cable as short as possible in order to minimize power losses.
