33972 datasheet(23/32 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33972

TYPICAL APPLICATIONS

INTRODUCTION

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

current to the 1.5 k

Ω 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 flyback 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 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.

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

SP0

SG0

SG13

2.0

4.0V Ref

Comparator

To SPI

VPWR

SG0

1.5k

VBAT

AMUX

100k

VPWR

Comparator

To SPI

4.0V

Ref

2.0

2.0mA

VPWR

SG0

2.0

VPWR

Comparator

To SPI

4.0V Ref

SG13

Table 21. Sleep Mode Power Supply

MCU

VDD

33972

VDD

Comments

5.0 V

All wake-up conditions apply. (Refer to Sleep

Mode, page 19.)

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

33972 in Normal mode.

0 V

SPI wake-up is not possible.

VSGn = ISGn x 1.5kΩ + VDS

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