33975 Datasheet, PDF (24/32 Pages) Freescale Semiconductor, Inc – Multiple Switch Detection Interface with Suppressed Wake-Up and 32mA Wetting Current

TYPICAL APPLICATIONS
OPERATIONAL MODES
VBAT
750 Ω
100 kΩ
SG0
SP0
V_PWR V_PWR
32
4.0
mA
mA
SG0
4.0 V Ref
+
-
To SPI
Comparator
V_PWR V_PWR
32
4.0
mA
mA
SG0
16
mA
4.0 V
Ref
+
-
To SPI
Comparator
2.0 mA
AMUX
SG13
V_PWR V_PWR
32
4.0
mA
mA
SG13
4.0 V Ref
+
-
To SPI
Comparator
Figure 14. 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
wetting current timer (refer to Table 9, page 16).
• metallic command –Set SPn to 16/32 mA or 2.0/4.0 mA
gate drive current (refer to Table 8, page 15).
• settings command –Set SPn as switch-to-battery (refer
to Table 6, page 14).
• tri-state command –Disable tri-state for SPn (refer to
Table 10, page 16).
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 terminal
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 Ω resistor, the analog voltage on the SGn
terminal will be approximately:
V_SGn = I_SGn x 750Ω + V_DS
As the voltage on the drain of the MOSFET increases, so
does the voltage on the SGn terminal. With the SGn terminal
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 V_PWR may damage the IC.
The SP0–SP7 terminals 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.
Table 21. Sleep Mode Power Supply
MCU
VDD
5.0 V
33975
VDD
Comments
5.0 V All wake-up conditions apply. (Refer to Sleep
Mode, page 20.)
5.0 V 0 V ^{SPI wake-up is not possible.}
0 V 5.0 V ^{Sleep mode not possible. Current from CS pull}
up will flow through MCU to VDD that has been
switched off. Negative edge of CS will put 33975
in Normal mode.
0V
0 V ^{SPI wake-up is not possible.}
33975
24
Analog Integrated Circuit Device Data
Freescale Semiconductor