参数资料
型号: LM8500IMT9/NOPB
厂商: NATIONAL SEMICONDUCTOR CORP
元件分类: 消费家电
英文描述: SPECIALTY CONSUMER CIRCUIT, PDSO48
封装: TSSOP-48
文件页数: 7/20页
文件大小: 327K
代理商: LM8500IMT9/NOPB
13.0 Brownout Reset (Continued)
The internal reset will not be turned off until t
id counts down
to zero. The internal reset will perform the same functions as
external reset. The device is guaranteed to operate at the
specified frequency down to the specified brownout voltage.
After the underflow, the logic is designed such that no addi-
tional internal resets occur as long as V
CC remains above
the brownout voltage.
The device is relatively immune to short duration negative
going V
CC transients (glitches). Proper filtering of the VCC
power supply voltage is essential for proper brownout func-
tionality. Power supply decoupling is vital even in battery
powered systems.
There are two optional brownout voltages. The part numbers
for the two versions of this device are:
LM8500, V
bor = high voltage range.
LM8300, V
bor = low voltage range.
Refer to the device specifications for the actual V
bor volt-
ages.
High brownout voltage devices are guaranteed to operate at
10MHz down to the high brownout voltage. Low brownout
voltage devices are guaranteed to operate at 3.33MHz down
to the low brownout voltage. Low brownout voltage devices
are not guaranteed to operate at 10MHz down to the low
brownout voltage.
Under no circumstances should the RESET pin be allowed
to float. The RESET input may be connected to an external
pull-up resistor to V
CC or to other external circuitry. The
output of the brownout reset detector will always preset t
id to
a value between 120-128s for the LM8500 and 360-384s
for the LM8300. At this time, the internal reset will be gener-
ated.
The device has a built in watchdog monitoring module to
prevent runaway code. To use the watchdog feature, the
WD_OUT pin must be connected to the RESET pin. The
WD_OUT pin has an internal weak pull-up so that, when the
WD_OUT pin is connected to the RESET pin, the RESET pin
does not require an external pull-up resistor to V
CC.
14.0 Calibration
The device supports two, five, and thirteen point calibration.
If desired, the calibration points can be stored internally in
the non-volatile storage element. During calibration time, the
device has the unique ability to check if the calibration points
make sense. For instance, if the desired calibration point
was to be at the upper left hand corner, but by accident, the
actual point detected was at the lower right hand corner, the
device will reject this point. This ensures the calibration
process is not performed incorrectly.
The calibration checking, can be enabled or disabled. If the
calibration checking is enabled, the controller will always
check the current calibration point being done against the
theoretical point and determine if the value is within ±127 of
the raw A/D values. If this option is desired, the touch screen
driver must perform the calibration according to the calibra-
tion mapping for the two, five, and thirteen points as shown
in Figure 5, Figure 6, and Figure 7, respectively. The theo-
retical values for the two, five, and thirteen points are shown
20037206
FIGURE 4. Brownout Reset Operation
LM8300/LM8500
www.national.com
15
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