Datasheet > 1338

1338

更新时间： 2023-12-20 18:46:33

品牌	Logo	应用领域
瑞萨 - RENESAS		电池
页数	文件大小	规格书
24页	1033K
描述
Real-Time Clock With Battery Backed Non-Volatile RAM

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1338 数据手册

1338 Datasheet

Typical Operating Circuit

CRYSTAL

V_CC

10k

SCL

SQW/OUT

CPU

IDT1338

V_BAT

SDA

GND

Detailed Description

The following sections discuss in detail the Oscillator

block, Power Control block, Clock/Calendar Register

Block and Serial I²C block.

Oscillator Block

Selection of the right crystal, correct load capacitance

and careful PCB layout are important for a stable crystal

oscillator. Due to the optimization for the lowest possible

current in the design for these oscillators, losses caused

by parasitic currents can have a significant impact on the

overall oscillator performance. Extra care needs to be

taken to maintain a certain quality and cleanliness of the

PCB.

Crystal Selection

The key parameters when selecting a 32 kHz crystal to

work with 1338 RTC are:

In the above figure, X1 and X2 are the crystal pins of our

device. Cin1 and Cin2 are the internal capacitors which

include the X1 and X2 pin capacitance. Cex1 and Cex2

are the external capacitors that are needed to tune the

crystal frequency. Ct1 and Ct2 are the PCB trace

capacitances between the crystal and the device pins.

CS is the shunt capacitance of the crystal (as specified in

the crystal manufacturer's datasheet or measured using a

network analyzer). Cex1 and Cex2 are not needed if the

crystal circuit uses the recommended crystal with

specified load capacitance (CL) of 12.5pF.

• Recommended Load Capacitance

• Crystal Effective Series Resistance (ESR)

• Frequency Tolerance

Effective Load Capacitance

Please see diagram below for effective load capacitance

calculation. The effective load capacitance (CL) should

match the recommended load capacitance of the crystal

in order for the crystal to oscillate at its specified parallel

resonant frequency with 0ppm frequency error.

Note: 1338CSRI integrates a standard 32.768 kHz

crystal in the package and contributes an additional

frequency error of 10ppm at nominal V_CC(+3.3 V) and

T_A=+25°C.

February 3, 2023

1 234 5 6 7...24

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