LTC1668IG

更新时间： 2024-01-03 22:41:16

品牌	Logo	应用领域
凌特 - Linear		转换器数模转换器光电二极管信息通信管理
页数	文件大小	规格书
16页	731K
描述
16-Bit, 50Msps DAC

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技术参数
数据手册

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LTC1668IG 技术参数

是否无铅：	含铅	是否Rohs认证：	符合
生命周期：	Active	包装说明：	SSOP,
针数：	28	Reach Compliance Code：	compliant
风险等级：	5.14	Is Samacsys：	N
最大模拟输出电压：	1 V	最小模拟输出电压：	-1 V
转换器类型：	D/A CONVERTER	输入位码：	BINARY
输入格式：	PARALLEL, WORD	JESD-30 代码：	R-PDSO-G28
JESD-609代码：	e3	长度：	10.2 mm
最大线性误差 (EL)：	0.0122%	湿度敏感等级：	1
标称负供电电压：	-5 V	位数：	16
功能数量：	1	端子数量：	28
最高工作温度：	85 °C	最低工作温度：	-40 °C
封装主体材料：	PLASTIC/EPOXY	封装代码：	SSOP
封装形状：	RECTANGULAR	封装形式：	SMALL OUTLINE, SHRINK PITCH
峰值回流温度（摄氏度）：	260	认证状态：	Not Qualified
座面最大高度：	2 mm	标称安定时间 (tstl)：	0.02 µs
标称供电电压：	5 V	表面贴装：	YES
技术：	BICMOS	温度等级：	INDUSTRIAL
端子面层：	Matte Tin (Sn)	端子形式：	GULL WING
端子节距：	0.65 mm	端子位置：	DUAL
处于峰值回流温度下的最长时间：	30	宽度：	5.3 mm
Base Number Matches：	1

LTC1668IG 数据手册

LTC1668

W U U

APPLICATIO S I FOR ATIO

For fixed reference voltage applications, C_COMP1should

be 0.1µF or more. The reference control loop small-signal

bandwidthisapproximately1/(2π)•C_COMP1•80or20kHz

for C_COMP1= 0.1µF.

Theory of Operation

The LTC1668 is a high speed current steering 16-Bit DAC

made on an advanced BiCMOS process. Precision thin

film resistors and well matched bipolar transistors result

in excellent DC linearity and stability. A low glitch current

switchingdesigngivesexcellentACperformanceatsample

rates up to 50Msps. The device is complete with a 2.5V

internal bandgap reference and edge triggered latches,

and sets a new standard for DAC applications requiring

very high dynamic range at output frequencies up to

several megahertz.

Internal Reference Output—REFOUT

The onboard 2.5V bandgap voltage reference drives the

REFOUT pin. It is trimmed and specified to drive a 2k

resistor tied from REFOUT to I_REFIN, corresponding to a

1.25mA load (I_OUTFS= 10mA). REFOUT has nominal

output impedance of 6Ω, or 0.24% per mA, so it must be

buffered to drive any additional external load. A 0.1µF

capacitor is required on the REFOUT pin for compensa-

tion. Note that this capacitor is required for stability, even

if the internal reference is not being used.

Referring to the Block Diagram, the DAC contains an array

of current sources that are steered to I_OUTAor I_OUTBwith

NMOS differential current switches. The four most signifi-

cant bits, DB15 to DB12 are made up of 15 current

segmentsofequalweight. Thelowerbits, DB11toDB0are

binary weighted, using a combination of current scaling

and a differential resistive attenuator ladder. All bits and

segments are precisely matched, both in current weight

forDClinearity, andinswitchtimingforlowglitchimpulse

and low spurious tone AC performance.

DAC Transfer Function

The LTC1668 uses straight binary digital coding. The

complementary current outputs, I_{OUT A}and I_{OUT B}, sink

current from 0 to I_OUTFS. For I_OUTFS= 10mA (nominal),

I_{OUT A}swings from 0mA when all bits are low (i.e., Code =

0) to 10mA when all bits are high (i.e., Code = 65535) (deci-

mal representation). I_{OUT B}is complementary to I_{OUT A}

I_{OUT A}and I_{OUT B}are given by the following formulas:

Setting the Full-Scale Current, I_OUTFS

The full-scale DAC output current, I_OUTFS, is nominally

10mA, and can be adjusted down to 1mA. Placing a

resistor, R_SET, between the REFOUT pin, and the I_REFINpin

sets I_OUTFSas follows.

I_{OUT A}= I_OUTFS• (DAC Code/65536)

(2)

(3)

I_{OUT B}= I_OUTFS• (65535-DAC Code)/65536

In typical applications, the LTC1668 differential output

currents either drive a resistive load directly or drive an

equivalent resistive load through a transformer, or as the

feedback resistor of an I-to-V converter. The voltage

outputs generated by the I_{OUT A}and I_{OUT B}output currents

are then:

The internal reference control loop amplifier maintains a

virtual ground at I_REFINby servoing the internal current

source, I_INT, to sink the exact current flowing into I_REFIN

I_INTis a scaled replica of the DAC current sources and

I_OUTFS= 8 • (I_INT), therefore:

I_OUTFS= 8 • (I_REFIN) = 8 • (V_REF/R_SET

)

(1)

V_{OUT A}= I_{OUT A}• R_LOAD

V_{OUT B}= I_{OUT B}• R_LOAD

The differential voltage is:

V_DIFF= V_{OUT A}– V_{OUT B}

(4)

(5)

For example, if R_SET= 2k and is tied to V_REF= REFOUT =

2.5V, I_REFIN= 2.5/2k = 1.25mA and I_OUTFS= 8 • (1.25mA)

= 10mA.

(6)

The reference control loop requires a capacitor on the

COMP1 pin for compensation. For optimal AC perfor-

mance, C_COMP1should be connected to V_SSand be placed

very close to the package (less than 0.1").

= (I_{OUT A}– I_{OUT B}) • (R_LOAD

)

1...3 4 567 8 9...16

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