MC33298 datasheet(21/28 Pages) FREESCALE

tên linh kiện	MC33298

Giải thích chi tiết về linh kiện	Eight Output Switch with Serial Peripheral Interface I/O

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Analog Integrated Circuit Device Data

Freescale Semiconductor

21

33298

FUNCTIONAL DESCRIPTION

FAULT LOGIC OPERATION

Figure 19. Output OFF Open Load Fault

An Output OFF Open Load Fault is indicates when the

output voltage is less than the Output Threshold Voltage

(VThres) of 0.6 to 0.8 x VDD. Since the 33298 outputs function

as switches, during normal operation, each MOSFET output

should either be completely turned ON or OFF. By design,

the threshold voltage was selected to be between the ON and

OFF voltage of the MOSFET. During normal operation, the

ON state VDS voltage of the MOSFET is less than the

threshold voltage and the OFF state VDS voltage is greater

than the threshold voltage. This design approach provides

using the same threshold comparator for Output Open Load

Detect in the OFF state and Short Circuit Detect in the ON

state. See Figure 18 for an understanding of the Short Circuit

Detect circuit. With VDD = 5.0 V, an OFF state output voltage

of less than 3.0 V will be detected as an Output OFF Open

Load Fault while voltages greater than 4.0 V will not be

detected as a fault.

The 33298 has an internal pull-down current source of

50 µA, illustrated in Figure 17 between the MOSFET drain

and ground. This current source prevents the output from

floating up to VPWR if there is an open load or internal wire

bond failure. The internal comparator compares the drain

voltage with a reference voltage, VThres (0.6 to 0.8 x VDD). If

the output voltage is less than this reference voltage, the

33298 will declare the condition to be an open load fault.

During steady-state operation, the minimum load

resistance (RL) required to prevent false fault reporting during

normal operation can be located using the following equation:

Therefore, the load resistance necessary to prevent false

open load fault reporting is (using Ohm’s Law) equal to 92 k

Ω

or less

.

During output switching, especially with capacitive loads,

a false output OFF Open Load Fault may be triggered. To

prevent this false fault from being reported an internal fault

filter in the range of 25 to 100 µs is incorporated. The duration

in which a false fault may be reported is a function of the load

impedance (RL,CL,LL), RDS(on), and COUT of the MOSFET as

well as the supply voltage (VPWR). The rising edge of CS

triggers a built-in fault delay timer which must time-out (25 or

100 µs) before the fault comparator is enabled to detect at

faulted threshold. The circuit automatically returns to normal

operation once the condition causing the Open Load Fault is

removed.

SHORTED LOAD FAULT

A short load, or over current fault can be caused by any

output being shorted directly to supply, or an output

experiencing a current greater than the current limit.

There are three safety circuits progressively in operation

during load short conditions providing system protection.

They are:

1. The output current of the device is monitored in an

analog fashion using a SENSEFET

™ approach and

current limited.

2. The output current of the device is sensed by

monitoring the MOSFET drain voltage.

3. The output thermal limit of the device is sensed, and

when attained, causes only the specific faulted output

to be latched OFF, allowing all remaining outputs to

operate normally.

Each of the three protection mechanisms are incorporated

in their output providing robust independent output operation.

The analog current limit circuit is always active, monitoring

the output drain current. An over current condition causes the

gate control circuitry to reduce the gate-to-source voltage

imposed on the output MOSFET, re-establishing the load

current in compliance with current limit (1.0 to 3.0 A) range.

Time required for the current limit circuitry to act is less than

20 µs. Therefore, currents higher than 1.0 to 3.0 A will never

be seen for more than 20 µs (a typical duration is 10 µs). If

the current of an output attempts to exceed the

predetermined limit of 1.0 to 3.0 A (2.0 A nominal), the VDS

voltage will exceed the VThres voltage and the over current

comparator will be tripped, illustrated in Figure 18.

Figure 20. Short Circuit Detect and

Analog Current Limiting Circuit

The status of SFPD determines whether the 33298 will

shut down immediately, or continue to operate in an analog

VThres

2.5 to 3.5 V

+

–

Low = Fault

50 µA

Output

VPWR

RL

33298

MOSFET OFF

VThres

2.5 to 3.5 V

+

–

High = Fault

Output

VPWR

RL

33298

+

–

MOSFET ON

Digital

Analog

Vref

Số phần tương tự - MC33298

nhà sản xuất	tên linh kiện	bảng dữ liệu	Giải thích chi tiết về linh kiện
Freescale Semiconductor...	MC33298	643Kb / 28P	Eight Output Switch with Serial Peripheral Interface I/O
Motorola, Inc	MC33298	1Mb / 23P	Eight Output Switch with Serial Peripheral Interface I/O
NXP Semiconductors	MC33298	966Kb / 28P	Eight Output Switch with Serial Peripheral Interface I/O Rev. 6.0, 4/2008
Freescale Semiconductor...	MC33298DW	643Kb / 28P	Eight Output Switch with Serial Peripheral Interface I/O
NXP Semiconductors	MC33298DW	966Kb / 28P	Eight Output Switch with Serial Peripheral Interface I/O Rev. 6.0, 4/2008

More results

Mô tả tương tự - MC33298

nhà sản xuất	tên linh kiện	bảng dữ liệu	Giải thích chi tiết về linh kiện
Freescale Semiconductor...	33291L	593Kb / 25P	Eight-Output Switch with Serial Peripheral Interface I/O
NXP Semiconductors	MC33298	966Kb / 28P	Eight Output Switch with Serial Peripheral Interface I/O Rev. 6.0, 4/2008
Motorola, Inc	MC33291	633Kb / 24P	Eight Output Switch with Serial Peripheral Interface I/O
Freescale Semiconductor...	33291	558Kb / 26P	Eight-Output Switch with Serial Peripheral Interface I/O
	MC33298	643Kb / 28P	Eight Output Switch with Serial Peripheral Interface I/O
	33291	1Mb / 27P	Eight-Output Switch with Serial Peripheral Interface I/O
Motorola, Inc	MC33298	1Mb / 23P	Eight Output Switch with Serial Peripheral Interface I/O
Freescale Semiconductor...	33291L	1Mb / 26P	Eight-Output Switch with Serial Peripheral Interface I/O
NXP Semiconductors	MC33291	901Kb / 27P	Eight-Output Switch with Serial Peripheral Interface I/O Rev 5, 07/2008
Freescale Semiconductor...	33880	590Kb / 25P	Configurable Octal Serial Switch with Serial Peripheral Interface I/O

More results

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