MC33993DWB Ver la hoja de datos (PDF) - Motorola => Freescale

Número de pieza

componentes Descripción

Fabricante

MC33993DWB

MULTIPLE SWITCH DETECTION INTERFACE

Motorola => Freescale 

VBAT

33993

SP0

SP1

VPWR

VDD

VBAT

I1

2.0 mA

VDD

SP7

SG0

SG1

VPWR VPWR

16

2.0

mA

mA

SG12

WAKE

SI

SCLK

CS

SO

INT

AMUX

R1

VPWR VPWR

Analog Sensor

or Analog Switch

16

mA

2.0

mA

SG13

MCU

MOSI

SCLK

CS

MISO

INT

AN0

Analog

Ports

I2

2.0 mA

4.54 V to 5.02 V

2.39 kΩ

0.1%

R2

VREF(H)

VREF(L)

Figure 11. Analog Ratiometric Conversion

To read a potentiometer sensor, the wiper should be

grounded and brought back to the module ground, as illustrated

in Figure 11. With the wiper changing the impedance of the -

sensor, the analog voltage on the input will represent the

position of the sensor.

Using the Analog feature to provide 2.0 mA of pull-up current

to an analog sensor may induce error due to the accuracy of the

current source. For this reason, a ratiometric conversion must

be considered. Using two current sources (one for the sensor

and one to set the reference voltage to the A/D converter) will

yield a maximum error (owing to the 33993) of 4%.

Higher accuracy may be achieved through module level

calibration. In this example, we use the resistor values from

Figure 11 and assume the current sources are 4% from each

other. The user may use the module end-of-line tester to

calculate the error in the A/D conversion. By placing a 2.0 kΩ,

0.1% resistor in the end-of-line test equipment and assuming a

perfect 2.0 mA current source from the 33993, a calculated A/D

conversion may be obtained. Using the equation yields the

following:

I1 x R1

ADC =

x 225

I2 x R2

2.0 mA x 2.0 kΩ

ADC =

x 225

2.0 mA x 2.39 kΩ

ADC = 213 counts

The ADC value of 213 counts is the value with 0% error

(neglecting the resistor tolerance and AMUX input offset

voltage). Now we can calculate the count value induced by the

mismatch in current sources. From a sample device the

maximum current source was measured at 2.05 mA and

minimum current source was measured at 1.99 mA. This yields

3% error in A/D conversion. The A/D measurement will be as

follows:

1.99 mA x 2.0 kΩ

ADC =

x 225

2.05 mA x 2.39 kΩ

ADC = 207 counts

This A/D conversion is 3% low in value. The error correction

factor of 1.03 may be used to correct the value:

ADC = 207 counts x 1.03

ADC = 213 counts

An error correction factor may then be stored in E2 memory

and used in the A/D calculation for the specific input. Each input

used as analog measurement will have a dedicated calibrated

error correction factor.

Power MOSFET/LED Driver and Monitor

Because of the flexible programming of the 33993 device, it

may be used to drive small loads like LEDs or MOSFET gates.

It was specifically designed to power up in the Normal mode

with the inputs tri-state. This was done to ensure the LEDs or

MOSFETs connected to the 33993 power up in the off-state.

The Switch Programmable (SP0–SP7) inputs have a source-

and-sink capability, providing effective MOSFET gate control.

To complete the circuit, a pull-down resistor should be used to

keep the gate from floating during the Sleep modes. Figure 12,

page 22, shows an application where the SG0 input is used to

monitor the drain-to-source voltage of the external MOSFET.

The 1.5 kΩ resistor is used to set the drain-to-source trip

voltage. With the 2.0 mA current source enabled, an interrupt

will be generated when the drain-to-source voltage is

approximately 1.0 V.

MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA

33993/D

21

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