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LMH1983SQ

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LMH1983SQ 数据手册

National Semiconductor

Application Note 2108

Mark Sauerwald

Generating 44.1 kHz Based

Clocks with the LMH1983

December 15, 2010

Introduction

The LMH1983 is a highly integrated programmable audio / video (A/V) clock generator intended for broadcast and professional

applications. The programmable features allow for the generation of many different clocks and control signals. This application

note describes how to generate a 44.1 kHz audio clock using PLL4.

To generate a 44.1 kHz based clock with the LMH1983, make the following writes to the PLL4 Advance Control registers:

0x35 (Charge Pump Current): 0F'h

0x36 (R Counter): 7D'h

0x37 ( N Counter MSB): 03'h

0x38 ( N Counter LSB): 10'h

0x39 ( VCO Frequency): 66'h

To calculate these numbers you need to match the frequencies coming in to the phase comparator — the first of these fre-

quencies is 27 MHz / R. The second frequency is 44.1 kHz x 512 x 4 x 5 x 3 / (N*8) (assuming that the IS125 bit and the

PLL_DIV registers have not been changed from their default vaules.)

Setting these two equal to each other gives:

27 MHz * 8 * N = 44.1 kHz x 512 x 4 x 3 x R

Break 27 MHz and 44.1 kHz down into their prime factors:

27 MHz = 2⁶* 3³* 5⁶

44.1 kHz = 2²* 3²* 5²* 7²

therefore:

2⁹* 3³* 5⁶* N = 2¹³* 3³* 5³* 7²x R

simplifying:

5³* N = 2⁴* 7²* R

Therefore the following values were selected:

5³= 125 = 7D'h for R

2⁴* 7²= 784 = 0310'h for N

Since the frequency coming into the charge pump is about one half the default value, increase the charge pump current to

about twice the default value to compensate, then adjust the VCO center frequency to main stable lock.

301449

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型号	品牌	获取价格	描述	数据表
LMH1983SQ/NOPB	TI	获取价格	具有音频时钟的 3G/高清/标清视频时钟发生器 \| RTA \| 40 \| -40 to 8
LMH1983SQE/NOPB	TI	获取价格	具有音频时钟的 3G/高清/标清视频时钟发生器 \| RTA \| 40 \| -40 to 8
LMH1983SQX	NSC	获取价格	IC VIDEO CLOCK GENERATOR, QCC40, 6 X 6 MM, LLP-40, Clock Generator
LMH1983SQX/NOPB	TI	获取价格	具有音频时钟的 3G/高清/标清视频时钟发生器 \| RTA \| 40 \| -40 to 8
LMH2	CREE	获取价格	LMH2 LED Modules Family
LMH2100	NSC	获取价格	50 MHz to 4 GHz 40 dB Logarithmic Power Detector for CDMA and WCDMA
LMH2100	TI	获取价格	用于 CDMA 和 WCDMA 的 50MHz 至 4GHz 40dB 对数功率检测器
LMH2100TM	NSC	获取价格	50 MHz to 4 GHz 40 dB Logarithmic Power Detector for CDMA and WCDMA
LMH2100TM/NOPB	TI	获取价格	用于 CDMA 和 WCDMA 的 50MHz 至 4GHz 40dB 对数功率检测器 \|
LMH2100TMX	NSC	获取价格	50 MHz to 4 GHz 40 dB Logarithmic Power Detector for CDMA and WCDMA