33972_09 Datasheet, PDF (23/32 Pages) Freescale Semiconductor, Inc – Multiple Switch Detection Interface with Suppressed Wake-up

TYPICAL APPLICATIONS
INTRODUCTION
VBAT
current to the 1.5 kΩ resistor, the analog voltage on the SGn
pin will be approximately:
1.5kΩ
100kΩ
SG0
V_PWR V_PWR
16
2.0
mA
mA
SG0
SP0
4.0V Ref
+
-
To SPI
Comparator
V_PWR V_PWR
16
2.0
mA
mA
SG0
4.0V
+
-
To SPI
16
Ref
Comparator
mA
2.0mA
AMUX
SG13
V_PWR V_PWR
16
2.0
mA
mA
SG13
4.0V Ref
+
-
To SPI
Comparator
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
wetting current timer (refer to Table 9, page 15).
• metallic command –Set SPn to 16 or 2.0 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 SGn input
comparator. With the SGn input in tri-state, the load will pull
up the SGn input to battery. With open load 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 2.0 mA of
V_SGn = I_SGn x 1.5kΩ + V_DS
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 flyback voltages greater
than V_PWR 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 16 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 33972 DEVICES IN A MODULE SYSTEM
Connecting power to the 33972 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 33972 and their specific requirements for
functionality.
Table 21. Sleep Mode Power Supply
MCU
V_DD
5.0 V
33972
V_DD
5.0 V
Comments
All wake-up conditions apply. (Refer to Sleep
Mode, page 19.)
5.0 V
0V
0V
5.0 V
SPI wake-up is not possible.
Sleep mode not possible. Current from CS pull-
up will flow through MCU to V_DD that has been
switched off. Negative edge of CS will put
33972 in Normal mode.
0V
0 V SPI wake-up is not possible.
Multiple 33972 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
independently (refer to MCU Interface Description, page 13).
Therefore when sending the sleep command, one device will
enter sleep before the other. For multiple devices in a system,
it is recommended that the devices are controlled in serial (S0
Analog Integrated Circuit Device Data
Freescale Semiconductor
33972
23