A p p l i c at i o n N o t e AN3008 Renesas Solid State Relays for ATE Applications Authors: Van N. Tran Larry Sisken Wei Z. Jiang CEL Staff Application Engineer, CEL Opto Semiconductors CEL Product Marketing Manager, CEL Opto Semiconductors Graduate Intern (MSEE), SJSU 2.2 Reed Relays 1. Introduction A relay is used to isolate one electrical circuit from another. It uses a low current control circuit to make or break an electrically isolated high current circuit path. Relays come in a variety of forms, package styles, and technologies. For automatic test equipment (ATE) applications, the most common types are: Electro-Mechanical Relays (EMRs) Reed Relays Solid State Relays This Application Note will discuss the different types of relays and how Renesas addresses the technical demands and requirements of an expanding ATE market. 2. Overview: Types of Relays Coil Reed Reed Contact Figure 2-2 Reed Relay Switching in Reed Relays is also controlled by electromagnets. They differ from EMRs in that the electromagnets work directly on the contacts, rather than on anarmature. Two overlapping reeds are sealed in a long, narrow glass tube to protect the contacts from corrosion. A coil wraps the tube and when current is applied, the resulting magnetic field mechanicallly pulls the reeds together, closing the contacts and completing the circuit. 2.1 Electro-Mechanical Relays (EMRs) 2.3 Solid State Relays (SSRs) High Current Circuit Control Current Circuit Figure 2-1 Electro-Mechanical Relay An alternative to mechanical switching , Renesas solid state relays feature an infrared emitting diode (IRED) on their input side and a photo voltaic diode array (PVD), charge control circuitry and MOSFET switches on the output. Since they have no moving parts, SSRs are much more dependable and have a much longer lifetime than EMR or Reed relays. Infrared Emitting Diode (IRED) Photovoltaic Diode Array (PVD) MOSFET Output An EMR is an electromagnetic switch designed to open and close contacts. When current flows through the EMR’s coil, the resulting magnetic field mechanically moves an armature fitted with a contact. When this moving contact makes connecton with a fixed contact, the circuit is completed. When the current is removed, the armature returns to its relaxed position and the contacts are opened. EMRs are available in both latching and non-latching varieties. Non-latching relays require continuous current flow through the coil to keep the relay actuated. Latching relays employ permanent magnets to keep the armature in position, even after the drive current is removed from the coil. Figure 2-3 Solid State Relay 1 AN3008 2.4 SSRs vs EMRs/Reed Relays EMR and Reed relays are a good choice for applications that require high currents and very high voltages. But for designs requiring fast switching speeds, long service life, and a miniature footprint, SSRs have the advantage: Solid State Relays SSRs EMRs and Reed Relays AC Output Drive Excellent Excellent Small Analog Signal Excellent Good FEATURE Contol Large Current Good Excellent ON Resistance Good Excellent Switching Speed Good (µs–ns) Fair (ms) Low Input Drive Excellent (3–5mW) Poor (50–100 mW) CMR Excellent Poor Service Life Excellent Poor Size/Weight Small/Light Large/Heavy and the PVD voltage drops. In this condition, the charge stored in the MOSFET gate is not released quickly; the FET remains conductive until V2 - V1 is less than 0.7 V (See Figure 4-1 below). To speed switching, the thyristor/charge control turns on and quickly depletes the MOSFET gate charge, effectively dropping the gate voltage below the threshold level, and turning OFF the FET switch. Infrared Emitting Diode (IRED) Form A Relay: Single-Pole, Single-Throw, Normally Open Form B Relay: Single-Pole, Single-Throw, Normally Closed Form C Relay: Single-Pole, Double-Throw (Break-Before-Make) COUT: Off-state capacitance that results in isolation losses for high frequency signals RON: Finite on-channel resistance that results in power dissipation and current limitations 4. Normally-Open Relay: Theory of Operation When current is applied to the input, the IRED emits in frared light. Some of this light directly enters the PVD via a transparent silicon layer. The remaining light reaches the PVD after reflecting off this silicon layer’s surface. The PVD then generates a current corresponding to the amount of light radiation received. This current then passes through the charge control section of the SSR, raising the gate voltage on the output MOSFET switch. When this gate voltage reaches a threshold value, current flows between the MOSFET drain and source, and the external load circuit across the output terminals is closed or ON. When the input signal stops, the IRED stops emitting light MOSFET Output V1 V2 Thyristor / Charge Control Diode Stack Figure 2-4 SSRs vs. EMRs and Reed Relays 3. Common Terms Used with SSRs Photovoltaic Diode Array (PVD) Figure 4-1 Normally-Open Solid State Relay 5. SSR Load Connections Renesas SSRs have two N-Channel-type MOSFETs and can switch both AC and DC loads. With AC, one MOSFET switches the positive phase, the other switches the negative. In controlling a DC load, only one MOSFET is needed. The other can be configured to provide enhanced switching characteristics. Figure 5-1 illustrates the load connections possible: AC/DC Load Connection A 1 2 3 DC Load Connection B1 1 2 3 DC Load Connection B2 1 2 3 DC Load Connection C 1 2 3 6 5 4 AC/DC VL IL 6 5 IL LOAD LOAD + – DC VL 4 6 5 4 IL 6 IL 5 4 IL – LOAD LOAD IL + IL + DC VL + – DC VL Figure 5-1 AC and DC Load Connections using Renesas SSRs 2 AN3008 6. Renesas SSRs in ATE applications 7. Signal Bandwidth and Leakage Renesas has introduced its PS78XX Series of SSRs. Based on a Silicon on Insulator (SOI) process, they feature low CxR values and COUT of 1.0 pF or less. Housed in tiny, Mini Flat-Lead packages, they’re ideal for a variety of ATE applications (Figure 6-1). Depending upon the application, some PS78XX Series SSRs allow signals of up to 2GHz bandwidth to pass through the device without significant power loss (Figure 7-1, Page 4). However, due to the inverse relationship between COUT and RON in a MOSFET switch, there’s a trade-off between the signal that’s allowed through the switch when it’s ON. and the leakage signal when the switch is OFF. In other words, if COUT is high and the signal is allowed to pass through with low loss, the signal leakage will increase. As shown in Figure 7-2 (Page 4), high frequency signals will pass through, even when the SSR is OFF. This is due to the inherent output capacitance across the FET switch. To address the issue, the circuit designer may need to mask the signal through software control or other measures. These two graphs illustrate the relationship between insertion loss in the ON and OFF conditions. By carefully matching the Renesas SSR to the application, in sertion loss can be minimized when ON and maximized when OFF. 1 DUT 2 Test Function Unit 4 3 Parametric Measurement Unit Device Power Supply Figure 6-1 SSR ATE applications For switching high speed signals to a Device Under Test (DUT) - #1 above - Renesas offers highg speed SSRs with Equivalent Rise Times (ERT) of 45 to 50 ps (typ). To force or sense current, voltage, a short, or an open condition of the DUT (Parametric Measurement, #2 above) Renesas offeres SSRs with low C OUT X RON. Low COUT minimizes leakage current from high speed digital test signals, while low RON minimizes the power loss across the switch during testing. To power the DUT (3#), Renesas offers SSRs with low RON to minimize power loss across the switch. In feedback looks (#4), low CxR is required. Renesas offers a choice of SSR devices for this application. The table in Figure 6-2 below provides part numbers. FEATURE High Speed Pulse Response For Signal Integrity Low COUT x RON 1pF or less Low RON Low COUT x RON 1 2 3 8. Summary Key advantages for SSRs are: high reliability, low input power consumption, high packing densities, fast switch ing speeds, and they produce no signal “bouncing.” Renesas offers a variety of SSRs designed to enhance ATE performance and reliability — while reducing the system size, design headaches, and overall cost. 4 PS7801 PS7802A PS7801C PS7801D PS7801F PS7801M PS710B PS710E PS7113 PS720C PS7206 PS7801 PS7804 PS7802A PS7802B Figure 6-2 Recommended Renesas SSRs for ATE applications 3 AN3008 7. Signal Bandwidth and Leakage Figure 7-3 C & R Values Figure 7-1 Insertion loss of PS78XX Series when the IRED is ON, @ PIN = –20 dBm, IF = 5 mA 1 0 PS7802A S21 (dB) -1 PS7801C -2 PS7804 PS7801D Part No. C R PS7802A 11.5 PS7804 27 1.1 1.1 PS7801D 0.6 12 PS7801C 0.5 13 -3 -4 -5 -6 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 4.5 5.0 Frequency (GHz) Figure 7-2 Insertion loss of PS78XX Series when the IRED is OFF, @ PIN = –20 dBm 1 PS7804 0 S21 (dB) -1 PS7802A -2 -3 PS7801D -4 PS7801C -5 -6 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Frequency (GHz) Information and data presented here is subject to change without notice. California Eastern Laboratories assumes no responsibility for the use of any circuits described herein and makes no representations or warranties, expressed or implied, that such circuits are free from patent infringement. © California Eastern Laboratories 07.13 4590 Patrick Henry Drive, Santa Clara, CA 95054-1817 Tel. 408-919-2500 FAX 408-988-0279 www.cel.com 4