전자부품 데이터시트 검색엔진 |
|
FM33256B 데이터시트(PDF) 10 Page - Cypress Semiconductor |
|
FM33256B 데이터시트(HTML) 10 Page - Cypress Semiconductor |
10 / 29 page FM33256B SPI Companion w/ FRAM This product conforms to specifications per the terms of the Ramtron Ramtron International Corporation standard warranty. The product has completed Ramtron’s internal 1850 Ramtron Drive, Colorado Springs, CO 80921 qualification testing and has reached production status. (800) 545-FRAM, (719) 481-7000 www.ramtron.com Rev. 3.0 Aug. 2012 Page 10 of 28 Trickle Charger To facilitate capacitor backup, the VBAK pin can optionally provide a trickle charge current. When the VBC bit (register 18h bit 3) is set to a ‘1’, the VBAK pin will source approximately 80 µA until VBAK reaches VDD. This charges the capacitor to VDD without an external diode and resistor charger. There is a Fast Charge mode which is enabled by the FC bit (register 18h, bit 2). In this mode the trickle charger current is set to approximately 1 mA, allowing a large backup capacitor to charge more quickly. • In the case where no battery is used, the V BAK pin should be tied to VSS and VBC bit cleared. Note: systems using lithium batteries should clear the VBC bit to 0 to prevent battery charging. The VBAK circuitry includes an internal 1 K Ω series resistor as a safety element. The trickle charger is UL Recognized. Calibration When the CAL bit in register 00h is set to a ‘1’, the clock enters calibration mode. The FM33256B employs a digital method for calibrating the crystal oscillator frequency. The digital calibration scheme applies a digital correction to the RTC counters based on the calibration settings, CALS and CAL.4-0. In calibration mode (CAL=1), the ACS pin is driven with a 512 Hz (nominal) square wave and the alarm is temporarily unavailable. Any measured deviation from 512 Hz translates into a timekeeping error. The user measures the frequency and writes the appropriate correction value to the calibration register. The correction codes are listed in the table below. For convenience, the table also shows the frequency error in ppm. Positive ppm errors require a negative adjustment that removes pulses. Negative ppm errors require a positive correction that adds pulses. Positive ppm adjustments have the CALS (sign) bit set to 1, where as negative ppm adjustments have CALS = 0. After calibration, the clock will have a maximum error of ± 2.17 ppm or ± 0.09 minutes per month at the calibrated temperature. The user will not be able to see the effect of the calibration setting on the 512 Hz output. The addition or subtraction of digital pulses occurs after the 512 Hz output. The calibration setting is stored in F-RAM so it is not lost should the backup source fail. It is accessed with bits CAL.4-0 in register 01h. This value only can be written when the CAL bit is set to a 1. To exit the calibration mode, the user must clear the CAL bit to a logic 0. When the CAL bit is 0, the ACS pin will revert to the function according to Table 2. Crystal Type The crystal oscillator is designed to use a 12.5pF crystal without the need for external components, such as loading capacitors. The FM33256B device has built-in loading capacitors that match the crystal. If a 32.768kHz crystal is not used, an external oscillator may be connected to the FM33256B. Refer to Application Note AN407 for recommendations on how to implement this. Layout Recommendations The X1 and X2 crystal pins employ very high impedance circuits and the oscillator connected to these pins can be upset by noise or extra loading. To reduce RTC clock errors from signal switching noise, a guard ring should be placed around these pads and the guard ring grounded. High speed SPI traces should be routed away from the X1/X2 pads. The X1 and X2 trace lengths should be less than 5 mm. The use of a ground plane on the backside or inner board layer is preferred. See layout example. Red is the top layer, green is the bottom layer. |
유사한 부품 번호 - FM33256B |
|
유사한 설명 - FM33256B |
|
|
링크 URL |
개인정보취급방침 |
ALLDATASHEET.CO.KR |
ALLDATASHEET 가 귀하에 도움이 되셨나요? [ DONATE ] |
Alldatasheet는? | 광고문의 | 운영자에게 연락하기 | 개인정보취급방침 | 링크교환 | 제조사별 검색 All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |