0.5
Ω
/0.8
Ω
Low-Voltage, Dual SPDT
Analog Switches in UCSP
MAX4684/MAX4685
Pin Description
PIN
NAME
UCSP
NC_
IN_
COM_
NO_
V+
GND
A1, C1
A2, C2
A3, C3
A4, C4
B4
B1
µMAX
5, 7
4, 8
3, 9
2, 10
1
6
Analog Switch—Normally Closed Terminal
Digital Control Input
Analog Switch—Common Terminal
Analog Switch—Normally Open Terminal
Positive Supply Voltage Input
Ground
FUNCTION
Detailed Description
The MAX4684/MAX4685 are low on-resistance, low-
voltage, dual SPDT analog switches that operate from a
+1.8V to +5.5V supply. The devices are fully specified
for nominal 3V applications. The MAX4684/MAX4685
have break-before-make switching and fast switching
speeds (t
ON
= 50ns max, t
OFF
= 40ns max).
The MAX4684 offers asymmetrical normally closed
(NC) and normally open (NO) R
ON
for applications that
require asymmetrical loads (examples include speaker
headsets and internal speakers). The part features a
0.5Ω max R
ON
for its NC switch and a 0.8Ω max RON
for its NO switch at the 2.7V supply. The MAX4685 fea-
tures a 0.8Ω max on-resistance for both NO and NC
switches at the +2.7V supply.
Power-Supply Sequencing and
Overvoltage Protection
Caution: Do not exceed the absolute maximum rat-
ings because stresses beyond the listed ratings
may cause permanent damage to devices.
Proper power-supply sequencing is recommended for
all CMOS devices. Always apply V+ before applying
analog signals, especially if the analog signal is not
current limited. If this sequencing is not possible, and if
the analog inputs are not current limited to <20mA, add
a small signal diode (D1) as shown in Figure 1. Adding
a protection diode reduces the analog range to a diode
drop (about 0.7V) below V+ (for D1). R
ON
increases
slightly at low supply voltages. Maximum supply volt-
age (V+) must not exceed +6V. Protection diode D1
also protects against some overvoltage situations. No
damage will result on Figure 1’s circuit if the supply
voltage is below the absolute maximum rating applied
to an analog signal pin.
Applications Information
Digital Control Inputs
The MAX4684/MAX4685 logic inputs accept up to
+5.5V regardless of supply voltage. For example, with
a +3.3V supply, IN_ may be driven low to GND and
high to 5.5V. Driving IN_ rail-to-rail minimizes power
consumption. Logic levels for a +1.8V supply are 0.5V
(low) and 1.4V (high).
POSITIVE SUPPLY
D1
V+
Analog Signal Levels
Analog signals that range over the entire supply volt-
age (V+ to GND) are passed with very little change in
on-resistance (see
Typical Operating Characteristics).
The switches are bidirectional, so the NO_, NC_, and
COM_ pins can be either inputs or outputs.
NO
Vg
COM
MAX4684
MAX4685
GND
Figure 1. Overvoltage Protection Using Two External Blocking
Diodes
6
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