Cypress CY25819 Pin.Description, Overview, Input Frequency Range and Selection, Spread% Selection

CY25818/19

Pin.Description

Pin	Name	Description
1	XIN/CLK	Clock, Crystal, or Ceramic Resonator Input Pin.
2	Vss	Power Supply Ground.
3	S0	Digital Spread% Control Pin. 3-Level input (H-M-L). Default = M.
4	SSCLK	Modulated Spread Spectrum Output Clock. The output frequency is referenced to input frequency. Refer
		to Table 2 for the amount of modulation (Spread%).
5	REFCLK	Unmodulated Reference Clock Output. The unmodulated output frequency is the same as the input
		frequency.
6	PD#	Power-Down Control Pin. Default = H (Vdd).
7	Vdd	Positive Power Supply.
8	XOUT	Clock, Crystal, or Ceramic Resonator Output Pin. Leave this pin unconnected if an external clock is used
		at XIN pin.

Overview

The Cypress CY25818/19 products are Spread Spectrum Clock Generator (SSCG) ICs used for the purpose of reducing EMI found in today’s high-speed digital electronic systems. The devices use a Cypress proprietary phase-locked loop (PLL) and Spread Spectrum Clock (SSC) technology to synthesize and modulate the frequency of the input clock. By frequency modulating the clock, the measured EMI at the fundamental and harmonic frequencies is greatly reduced. This reduction in radiated energy can significantly reduce the cost of complying with regulatory agency requirements and improve time to market without degrading system perfor- mance.

The input frequency range is 8–16 MHz for the CY25818 and 16–32 MHz for the CY25819. Both products accept external clock, crystal, or ceramic resonator inputs.

The CY25818/19 provide separate modulated (SSCLK) and unmodulated reference (REFCLK) clock outputs which are the same frequency as the input clock frequency. Down spread frequency modulation can be selected by the user, based on three discrete values of Spread%. A separate power down function is also provided.

Table 2. Spread% Selection

The CY25818/19 products are available in an 8-pin SOIC (150-mil) package with a commercial operating temperature range of 0–70°C. Contact Cypress for availability of –40 to +85°C industrial temperature range operation or TSSOP package versions. Refer to the CY25568, CY25811, CY25812, and CY25814 products for other functions such as clock multiplication of 1×, 2×, or 4× to generate a wide range of Spread Spectrum output clocks from 4 to 128 MHz.

Input Frequency Range and Selection

CY25818/19 input frequency range is 8–32 MHz. This range is divided into two segments, as given in Table 1.

Table 1. Input and Output Frequency Selection

Product	Input/Output Frequency Range
CY25818	8–16 MHz
CY25819	16–32 MHz

Spread% Selection

CY25818/19 SSCG products provide Down-Spread frequency modulation. The amount of Spread% is selected by using 3-Level S0 digital input. Spread% values are given in Table 2.

XIN (MHz)	Product	S0 = 1	S0 = 0	S0 = M
		Down (%)	Down (%)	Down (%)
8–10	CY25818	–3.0	–2.2	–0.7
10–12	CY25818	–2.7	–1.9	–0.6
12–14	CY25818	–2.5	–1.8	–0.6
14–16	CY25818	–2.3	–1.7	–0.5
16–20	CY25819	–3.0	–2.2	–0.7
20–24	CY25819	–2.7	–1.9	–0.6
24–28	CY25819	–2.5	–1.8	–0.6
28–32	CY25819	–2.3	–1.7	–0.5

Document #: 38-07362 Rev. *B Page 2 of 7

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