SGM4583 Datasheet, PDF (11/17 Pages) SG Micro Corp – CMOS Analog Switch

SGM4583
APPLICATION INFORMATION
Power-Supply Considerations
Overview
The SGM4583 construction is typical of most CMOS analog
switch. It has three supply pins: VCC, VEE, and GND. VCC and
V_EE are used to drive the internal CMOS switches and set the
limits of the analog voltage on any switch. Reverse ESD
protection diodes are internally connected between each
analog-signal pin and both VCC and VEE. If any analog signal
exceeds V_CC or V_EE, one of these diodes will conduct. During
normal operation, these and other reverse-biased ESD diodes
leak, forming the only current drawn from V_CC or V_EE.
Virtually all the analog leakage current comes from the ESD
diodes. Although the ESD diodes on a given signal pin are
identical and therefore fairly well balanced, they are reverse
biased differently. Each is biased by either VCC or VEE and the
analog signal. This means their leakages will vary as the signal
varies. The difference in the two diode leakages to the VCC and
V_EE pins constitutes the analog-signal-path leakage current. All
analog leakage current flows between each pin and one of the
supply terminals, not to the other switch terminal. This is why
both sides of a given switch can show leakage currents of either
the same or opposite polarity.
There is no connection between the analog-signal paths and
GND. VCC and GND power the internal logic and logic-level
translators, and set the input logic limits. The logic-level
translators convert the logic levels into switched VCC and VEE
signals to drive the gates of the analog signals. This drive signal
is the only connection between the logic supplies and signals
and the analog supplies. V_CC and V_EE have ESD-protection
diodes to GND.
Bipolar Supplies
This device operates with bipolar supplies between ±1.8V and
±5.5V. The VCC and VEE supplies need not be symmetrical, but
their sum cannot exceed the +13.2V absolute maximum rating.
Single Supply
This device operates from a single supply between +3.6V and
+11V when V_EE is connected to GND. All of the bipolar
precautions must be observed. At room temperature, it actually
“works” with a single supply near or below +2.5V, although as
supply voltage decreases, switch on-resistance and switching
times become very high.
High Voltage, CMOS Analog Switch
Over-Voltage Protection
Proper power-supply sequencing is recommended for the
CMOS device. Do not exceed the absolute maximum ratings
because stresses beyond the listed ratings can cause
permanent damage to the devices. Always sequence VCC on
first, then V_EE, followed by the logic inputs and analog signals. If
power-supply sequencing is not possible, add two small signal
diodes (D1, D2) in series with the supply pins for over-voltage
protection (Figure 1). Adding diodes reduces the analog-signal
range to one diode drop below V_CC and one diode drop above
VEE, but does not affect the device’s low switch resistance and
low leakage characteristics. Device operation is unchanged,
and the difference between VCC and VEE should not exceed
13.2V. These protection diodes are not recommended when
using a single supply if signal levels must extend to ground.
SGM4583
VCC
D1
EXTERNAL
BLOCKING DIODE
*
X,Y,Z
*
*
X_,Y_,Z_
*
D2
EXTERNAL
BLOCKING DIODE
*INTERNAL PROTECTION DIODES
Figure 1. Over-Voltage Protection Using External Blocking Diodes
SG Micro Corp
11
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