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| 型號： | YKNIFEX4HW |
| 英文描述： | IC APEX 20KE FPGA 100K |
| 中文描述： | 耶洛奈夫參考平臺硬件設(shè)計手冊 |
| 文件頁數(shù)： | 7/24頁 |
| 文件大?。?/td> | 186K |
| 代理商： | YKNIFEX4HW |
Yellowknife X4 Hardware Reference Manual
Page 14 /22
Motorola Inc.
Unrestricted Distribution Permitted
98 Feb 20
The NVRAM is provided by an external battery and an on-board static RAM. This is dif-
ferent from the previous generation of Motorola platforms which used integrated battery/
crystal/NVRAM/RTC modules from various vendors. A four-pin “Berg” header provides
a connection to an external (usually lithium) 4.5V battery pack. The header is designed so
that orientation is unimportant; however it is also diode-protected against reverse connec-
tions in the event the connector is installed offset by one, or if a two-pin header is used on
the battery.
The Super I/O has rather stringent requirements on the relationship of VBAT and VST-
DBY, as follows:
VBAT < VSTDBY - 0.5V
VBAT < VSTDBY * 1.2
Unless all of these requirements are met, the APC will not work. In order to meet these
requirements, Yellowknife uses a voltage divider network to trim the VBAT to an accept-
able level needed by the Super I/O. Since the current requirements are very small (less
than 20 uA), high-valued resistors can be used to minimize wasted power.
FIGURE 7. VBAT Trim
The protected, trimmed battery voltage is connected to the APC of the Super I/O control-
ler, which maintains the real-time clock and the power supply controller management.
That subsystem handles the switching between battery and main power, but similar cir-
cuitry is needed for the external RAM. To maintain storage at lower power, a low-voltage
SRAM is used (made by several vendors in a JEDEC standard package).
The above networks shows that the SRAM is typically powered by the standby voltage of
the ATX power supply, so VBAT drain is minimized as long as the power supply is
plugged in and AC mains are operating. Only when the system is unplugged does VST-
DBY = 0V, and the supply current for the SRAM+RTC+APC drops to less than 5uA.
This low current results in a VF of the Schottky diodes (1N5817) of approximately 0.25V,
so the battery can maintain the system over its expected lifetime as long as the battery
voltage is above 3.0V.
Battery
15K
100K
Conn.
VBAT
VSRAM
VSTDBY
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