參數(shù)資料
型號: M41T00AUDD1E
廠商: STMICROELECTRONICS
元件分類: 時(shí)鐘/數(shù)據(jù)恢復(fù)及定時(shí)提取
英文描述: REAL TIME CLOCK, DSO16
封裝: 5 X 4 MM, ROHS COMPLIANT, DFN-16
文件頁數(shù): 16/42頁
文件大?。?/td> 333K
代理商: M41T00AUDD1E
M41T00AUD
M41T00AUD clock operation
5.5
Trickle charge circuit
The M41T00AUD includes a trickle charge circuit to be used with a backup capacitor. It is
illustrated in Figure 14. VBACK is a bi-directional pin. Its primary function is as the backup
supply input. (The input nature is not depicted in the figure.) The trickle charge output
function is a secondary capability, and reduces the need for external components.
To enable trickle charging, two switches must be closed. A diode is present to prevent
current from flowing backwards from VBACK to VCC. A current limiting resistor is also in the
path.
An additional switch allows the diode to be bypassed through a 20 k resistor. This should
charge the capacitor to a higher level thus extending backup life. This switch automatically
opens when the device switches to backup thus preventing capacitor discharge to VCC.
Furthermore, at switchover to backup, the other switches open as well. The application
must close them after power-up to re-enable the trickle charge function.
The use of two switches in the chain is to protect against accidental, unwanted charging as
might be the case when using battery backup. Additionally, one of the two switches requires
four bits to be changed from the default value before it will close. This prevents single bit
errors from closing the switch. The four bits, TCHE3:TCHE0, reside in register 09h at bits
D3 to D0.
The control bit for the second switch, TCH2, resides in register 08h at bit D5. With this bit in
a separate register, two bytes must be written before charging will occur, again protecting
against inadvertent charging due to errors.
The control bit for the bypass switch, TCFE, resides in register 09h at bit D6.
To enable trickle charging, the user must set TCHE3:TCHE0 to 5h, and TCH2 to 1. To
bypass the diode, TCFE must be set to 1. All three fields must be enabled after each power-
up.
Figure 14.
Trickle charge circuit
TCHE
VCC
TCHE/ = 5h
OPEN
TCHE = 5h
CLOSED
VBACK
TCH2
TCH2 = 0
OPEN
TCH2 = 1
CLOSED
TCFE
TCFE = 0
OPEN
TCFE=1
CLOSED
ai13327
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