DS1308U-3+【PDF 16/16 页】IC RTC 56BYTE NVRAM I2C 8UMAX

收藏本站

您好，
买卖IC网欢迎您。
请登录
免费注册

买卖IC网

Sheet目录1993

12页 13页 14页 15页 [16页]

DS1308

Low-Current I2C RTC with 56-Byte NV RAM

Maxim Integrated

Freshness Seal Mode

When a battery is first attached to the device, the device

does not immediately provide battery-backup power to

the RTC or internal circuitry. After VCC exceeds VPF,

the devices leave the freshness seal mode and provide

battery-backup power whenever VCC subsequently falls

below VBAT. This mode allows attachment of the battery

during product manufacturing, but no battery capacity is

consumed until after the system has been activated for

the first time. As a result, minimum battery energy is used

during storage and shipping.

Oscillator Circuit

The DS1308 uses an external 6pF 32.768kHz crystal. The

oscillator circuit does not require any external resistors or

capacitors to operate. See Table 2 for the external crystal

parameters. The Functional Diagram shows a simplified

schematic of the oscillator circuit. The startup time is

usually less than 1 second when using a crystal with the

specified characteristics.

Whenever VCC > VPF, a 5Fs glitch filter at the output of

the crystal oscillator is enabled.

Clock Accuracy

The accuracy of the clock is dependent upon the

accuracy of the crystal and the accuracy of the match

between the capacitive load of the oscillator circuit and

the capacitive load for which the crystal was trimmed.

Crystal frequency drift caused by temperature shifts

creates additional error. External circuit noise coupled

into the oscillator circuit can result in the clock running

fast. Figure 3 shows a typical PCB layout for isolating

the crystal and oscillator from noise. Refer to Application

Note 58: Crystal Considerations with Maxim Real-Time

Clocks (RTCs) for detailed information.

Table 1. Power Control

Table 2. Crystal Specifications

Note: The crystal, traces, and crystal input pins should be isolated from RF generat-

ing signals. Refer to Application Note 58: Crystal Considerations for Maxim Real-Time

Clocks (RTCs) for additional specifications.

Figure 3. Typical PCB Layout for Crystal

SUPPLY CONDITION

READ/WRITE

ACCESS

POWERED

VCC < VPF, VCC < VBAT

VBAT

VCC < VPF, VCC > VBAT

VCC

VCC > VPF, VCC < VBAT

Yes

VCC

VCC > VPF, VCC > VBAT

Yes

VCC

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

Nominal Frequency

32.768

kHz

Series Resistance

ESR

100

Load Capacitance

CRYSTAL

GND

LOCAL GROUND PLANE (LAYER 2)

NOTE: AVOID ROUTING SIGNALS IN THE CROSSHATCHED AREA (UPPER LEFT-HAND

QUADRANT) OF THE PACKAGE UNLESS THERE IS A GROUND PLANE BETWEEN THE

SIGNAL LINE AND THE PACKAGE.

发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

*型号	*数量	厂商	批号	封装

添加更多采购

采购需求

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

我的联系方式