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
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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
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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
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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
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Tel. 408-919-2500
FAX 408-988-0279 www.cel.com
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