Analog Integrated Circuit Device Data
Freescale Semiconductor
25
33975
TYPICAL APPLICATIONS
OPERATIONAL MODES
Figure 15. MOSFET or LED Driver Output
The sequence of commands (from Normal mode with inputs
tri-state) required to set up the device to drive a MOSFET are
as follows:
wetting current timer enable command –Disable SPn
metallic command –Set SPn to 16/32 mA or 2.0/4.0 mA
settings command –Set SPn as switch-to-battery (refer
tri-state command –Disable tri-state for SPn (refer to
After the tri-state command has been sent (tri-state disable),
the MOSFET gate will be pulled to ground. From this point
forward the MOSFET may be turned on and off by sending
the settings command:
settings command –SPn as switch-to-ground
(MOSFET ON).
settings command –SPn as switch-to-battery
(MOSFET OFF).
Monitoring of the MOSFET drain in the OFF state provides
open load detection. This is done by using an input
comparator. With the SGn input in tri-state, the load will pull
up the input to battery. With the load open, the SGn pin is
pulled down to ground through an external resistor. The open
load is indicated by a logic [1] in the SO data bit.
The analog command may be used to monitor the drain
voltage in the MOSFET ON state. By sourcing 4.0 mA of
current to the 750
resistor, the analog voltage on the SGn
pin will be approximately:
As the voltage on the drain of the MOSFET increases, so
does the voltage on the SGn pin. With the SGn pin selected
as analog, the MCU may perform the A/D conversion.
Using this method for controlling unclamped inductive loads
is not recommended. Inductive fly-back voltages greater than
VPWR may damage the IC.
The SP0–SP7 pins of this device may also be used to send
signals from one module to another. Operation is similar to
the gate control of a MOSFET.
For LED applications a resistor in series with the LED is
recommended but not required. The switch-to-ground inputs
are recommended for LED application. To drive the LED use
the following commands:
wetting current timer enable command –Disable SGn
wetting current timer.
metallic command –Set SGn to 32 mA.
From this point forward the LED may be turned on and off
using the tri-state command:
tri-state command –Disable tri-state for SGn (LED ON).
tri-state command –Enable tri-state for SGn (LED
OFF).
These parameters are easily programmed via SPI
commands in Normal mode.
Multiple 33975 Devices in a Module System
Connecting power to the 33975 and the MCU for Sleep mode
operation may be done in several ways.
Table 21 shows
several system configurations for power between the MCU
and the 33975 and their specific requirements for
functionality.
Multiple 33975 devices may be used in a module system. SPI
control may be done in parallel or serial. However when
parallel mode is used, each device is addressed
SP0
SG0
SG13
32
4.0
4.0 V Ref
+
-
Comparator
To SPI
VPWR
SG0
750
LO
A
D
VBAT
AMUX
100k
mA
VPWR
+
-
Comparator
To SPI
4.0 V
Ref
4.0
2.0 mA
16
mA
32
mA
VPWR
SG0
32
4.0
VPWR
mA
VPWR
+
Comparator
To SPI
4.0 V Ref
SG13
-
mA
Table 21. Sleep Mode Power Supply
MCU
VDD
33975
VDD
Comments
5.0V
All wake-up conditions apply. (Refer to
Sleep5.0V
0V
SPI wake-up is not possible.
0V
5.0V
Sleep mode is not possible. Current from the CS
pull-up will flow through the MCU to the VDD
that has been switched off. The negative edge
of CS will put 33975 in Normal mode.
0V
SPI wake-up is not possible.
VSGn = ISGn x 750 + VDS