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參數(shù)資料
| 型號： | MC68HC05V7 |
| 廠商： | Motorola, Inc. |
| 英文描述： | 8-Bit Microcontroller Units (MCU).(8位微控制器) |
| 中文描述： | 8位微控制器單元（MCU）。（8位微控制器） |
| 文件頁數(shù)： | 3/16頁 |
| 文件大小： | 295K |
| 代理商： | MC68HC05V7 |
AN1257/D
MOTOROLA
3
The power supply control logic enables the primary voltage regulator to be put into the power-conserving
standby mode through software, then to be re-enabled whenever the appropriate external conditions are
detected by the MCU. This enabling and disabling of the primary regulator is referred to as
power moding
.
Although the power supply control logic is always enabled, the small amount of circuitry requires a minimal
amount of current for normal operation, typically less than 100 A. This ensures that the MCU’s current
consumption is held to a minimum when the primary regulator is put into standby mode to conserve power.
The mask option-selectable LVR circuit, when enabled, allows the MCU to be held in a reset state
whenever the voltage at the V
DD
pins, whether supplied internally or externally, drops below the specified
threshold. This helps prevent incorrect operation during power-up, power-down, or brown-out situations.
POWER SUPPLY EXTERNAL CONFIGURATION AND CONTROL
Several MCU pins are directly involved in the operation of the integrated voltage regulator. In addition, a
few external components are recommended to help ensure stable operation of the voltage regulator.
These MCU pins and the external components recommended for proper operation are described below.
Figure 2 illustrates the hardware configuration and external components outlined in the description below.
The pin designations in Figure 2 refer to the MC68HC705V8 in the 68-pin plastic leaded chip carrier
(PLCC) package. This hardware description assumes the voltage regulator circuit has been properly
configured internally.
Voltage Regulator Input
The V
BATT
pin (pin 25) is the 12-volt input to the internal voltage regulator, with the ground return provided
through the two V
SSD
pins (pins 3 and 31). In automotive applications, the V
BATT
pin can be connected
directly to the vehicle’s battery, allowing the internal regulator to provide the 5-volt supply for the MCU.
However, voltage transients exceeding the maximum specifications of the V
BATT
pin are sometimes
encountered in automotive applications. For this reason, additional components may be necessary to
ensure the V
BATT
pin is not damaged if such a situation occurs. The circuit in Figure 2 includes an example
transient protection network between the vehicle’s battery and the V
BATT
pin to protect against this. To help
reduce the effects of temporary fluctuations in the 12-volt supply caused by noise and by changes in
loading on the vehicle's electrical system, a large capacitor (10
μ
F or greater) can be placed between the
12-volt supply and ground. If high frequency noise on the 12-volt supply is a problem, the user also can
add decoupling capacitors between V
BATT
and V
SSD
. Ceramic or polystyrene capacitors should be used to
provide noise rejection over a wide frequency range. If decoupling capacitors on the 12-volt supply are
used, they should be placed as close to the MCU pins as possible.
The V
IGN
pin (pin 29) is used to tell the power supply control logic when to enable the primary regulator.
The V
IGN
pin is an input pin designed to operate over an input voltage range equal to the supply voltage at
the V
BATT
pin. If a rising edge is detected at the V
IGN
pin and the primary regulator is in standby mode, the
primary regulator will transition to the normal operating mode, powering up the MCU. This feature can be
useful in those applications where a component or module is required to remain powered up but inactive
for long periods. This is common in the automotive environment, where a system may be required to
operate whether the vehicle ignition is switched on or not. In this type of application, the V
BATT
pin can be
connected to a constant 12-volt supply while the V
IGN
pin is connected to a switched 12-volt supply. Once
the switched supply is turned off, the application software can put the primary regulator into standby mode,
powering the MCU down to conserve energy until operation is again required. When the switched supply is
turned back on, the rising edge at the V
IGN
pin will cause the primary regulator to exit standby mode and
reactivate the MCU. This type of operation allows the MCU to conserve energy when activity is not
required, but to be reactivated immediately when necessary.
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