Maxim > Design=20 support > App = notes=20 > Analog=20 Switches and Multiplexers > APP = 638
Maxim > Design = support >=20 App = notes=20 > Audio=20 Circuits > APP 638
Maxim > Design = support >=20 App = notes=20 > Automotive=20 > APP 638

Sep 03, = 2002

Keywords: CMOS, analog switch, analogue = switch,=20 capacitive gate current ,MUX, multiplexers, = on-resistance, RON=20 flatness, THD, charge injection, ESD protected = multiplexers,=20 fault-protection, ESD protection, force-sense = switches=20
Related=20 parts

Download,=20 PDF format (143kB)
Download,=20 MOBI format (Kindle) [?] =

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APPLICATION NOTE 638

Selecting the Right CMOS Analog = Switch

Abstract: This=20 tutorial outlines the basic construction, operation, = and=20 applications of analog switches. On-resistance, = flatness, and=20 charge-injection, each a performance-related = specification,=20 are defined. Application-specific features including=20 ESD-protection, fault-protection, and force-sense = capability=20 are explained.

Attend=20 this brief webcast by Maxim on=20 = TechOnline

Also=20 see application note 4653, "FAQs about = analog=20 switches."

Introduction

First developed about 25 years = ago,=20 integrated analog switches often form the interface = between=20 analog signals and a digital controller.=20 This tutorial presents the theoretical basis for = analog=20 switches and describes some common applications for = them. The=20 special features of calibration multiplexers = (cal-muxes),=20 fault-protected switches, and force-sense=20 switches are discussed as well.

In recent = years,=20 integrated analog switches have offered better = switching=20 characteristics, lower supply voltages, and smaller = packages.=20 Because so many performance options and special = functions are=20 available, the well-informed product designer can = usually find=20 the right part for a particular application.

Standard Analog Switches

CMOS=20 analog switches are easy to use, so most designers = take them=20 for granted. But one should not forget that these = switches=20 solve specific engineering problems. Conventional = analog=20 switches like the early CD4066 or the MAX4066 = are now=20 offered by many semiconductor=20 manufacturers; their structure is shown in Figure = 1.=20 Maxim also offers devices such as the MAX4610, = which is=20 pin-for-pin compatible with the industry standard but = offers=20 better performance.

F= igure=20 1. The internal construction of a typical analog = switch=20 features parallel n- and p-channel=20 MOSFETs.

Connecting an n-channel MOSFET in = parallel=20 with a p-channel MOSFET allows signals to pass in = either=20 direction with equal ease. Whether the n- or the = p-channel=20 device carries more signal current depends on the = ratio of=20 input to output voltage. Because the switch has no = preferred=20 direction for current flow, it has no preferred input = or=20 output. The two MOSFETs are switched on and off by = internal=20 inverting and noninverting amplifiers. These = amplifiers=20 level-shift the digital input signal as required, = according to=20 whether the signal is CMOS- or TTL-logic-compatible = and=20 whether the analog supply voltage is single or = dual.

Low-Resistance Switches

Taking the p- and = n-channel=20 on-resistances (R_ON) in parallel (product = over sum)=20 for each level of V_IN yields a composite=20 on-resistance characteristic for the parallel = structure=20 (Figure 2). This plot of R_ON versus=20 V_IN can be described as linear=20 if you exclude the effects of temperature,=20 power-supply voltage, and R_ON variation = with analog=20 input voltage. You should be aware that these effects=20 represent disadvantages and that minimizing them is = often the=20 primary purpose of new products. See Table=20 1.

F= igure=20 2. The n-channel and p-channel on-resistances of = Figure 1 form=20 a low-valued composite=20 = on-resistance.

=

Ta= ble=20 1. Low-resistance switches=20 I_COM(OFF)/I_D(OFF)=20 (nA max) = = = = =

Part Number	Function	R_DS(ON) (=CE=A9 max)	R_ON = Match (=CE=A9 max)	R_ON = Flatness (=CE=A9 max	t_ON/t_OFF (ns=20 max)	Charge Injection (pC = typ)	Supply Voltage Range = (V)	Pin- Package
MAX312/MAX313/MAX314	4 SPST NC/NO/NO,NC	10	0.5	1.5	2	225/185	30	=C2=B14.5 to =C2=B120	16-DIP\|SO
MAX4614/MAX4615/MAX4616	4 SPST NO/NC/NO,NC	10	1	1	1	12/10	6.5	+2 to +5.5	14-DIP/SO/16-QSOP
MAX4617	8X1 Mux	10	1	1	1	15/10	3	+2 to +5.5	16-DIP/SO/QSOP
MAX4618	Dual 4X1 Mux	10	1	1	-	15/10	3	+2 to +5.5	16-DIP/SO\|QSOP
MAX4619	3 SPDT	10	1	1	-	15/10	3	+2 to +5.5	16-DIP\|SO\|6/QSOP
MAX4621	2 SPST NO	5	0.5	0.5	0.5	250/200	80	=C2=B14.5 to =C2=B120 or +4.5 to +36	16-DIP/SO
MAX4622	2 SPDT	5	0.5	0.5	0.5	250/200	80	=C2=B14.5 to =C2=B120 or +4.5 to +36	16-DIP/SO
MAX4623	2 DPST=20	5	0.5	0.5	0.5	250/200	80	=C2=B14.5 to =C2=B120 or +4.5 to +36	16-DIP/SO
MAX4661/MAX4662/MAX4663	4 SPST NO/NC/NO,NC	2.5	0.5	-	0.4	250/200	120	=C2=B14.5 to =C2=B120 or +4.5 to +36	16-DIP/SO\|/SSOP
MAX4664/MAX4665/MAX4666	4 SPST NO/NC/NO,NC	4	0.5	0.5	0.5	300/200	300	=C2=B14.5 to =C2=B120 or +4.5 to +36	16-DIP\|/SO
MAX4667/MAX4668/MAX4669	2 SPST NO/NC/NO,NC	2.5	0.5	0.4	0.4	300/200	450	=C2=B14.5 to =C2=B120 or +4.5 to +36	16-DIP/SO
MAX4680/MAX4690/MAX4694	2 SPST NO	1.25	0.5	0.25	0.3	275/200	-60	=C2=B14.5 to =C2=B120 or +4.5 to +36	16-DIP/WID SO/SSOP
MAX4734	1 4:1 MUX	0.8	1	0.2	0.1	25/20	60	+1.6 to +3.6	10-=C2=B5MAX=C2=AE 12-TQFN
MAX4741	2 SPST	0.8	1	0.08	0.18	24/16	28	1.6 to +3.6	8-SOT23
MAX4751	4 SPST NO	0.9	2.5	0.12	0.1	30/25	21	+1.6 to +3.6	14-TSSOP 16-QFN
MAX4756	4 SPDT=20 NO/NC	0.85	3	0.35	0.4	150/40	50	+1.8 to +5.5	36-UCSP=E2=84=A2 36-TQFN
MAX4780	4 2:1 MUX	1	1	0.15	0.2	25/10	5	+1.6 to +4.2	16-TQFN 16-TSSOP
MAX4781	1 8:1 MUX	1	2	0.4	0.2	25/15	40	+1.6 to +3.6	16-QFN 16-TSSOP
MAX4855	2 SPST NO/NC	1	2	0.12	0.27	60/40	170	+2 to +5.5	16-TQFN 16-TSSOP

The first=20 analog switches operated on =C2=B120V supply voltages = and had=20 several hundred ohms of R_ON. Recent = products (the=20 MAX4601, for=20 example) achieve 2.5=CE=A9 maximum R_ON with = a much lower=20 supply voltage. Supply voltage has a substantial = effect on=20 R_ON (Figure 3). The MAX4601 = specifies signal=20 and supply voltages from 4.5V to 36V or from = =C2=B14.5V to =C2=B120V. As=20 you can see, R_ON increases for lower supply = voltages. The max R_ON is about 8=CE=A9 at = 5V, 3=CE=A9 at 12V,=20 and only 2.5=CE=A9 at 24V. Many new analog switches = specify=20 low-voltage operation for supply voltages down to 2V. = For 5V=20 supplies, Figure 4 compares the Maxim switches = with=20 older types.

F= igure=20 3. Higher supply voltage causes lower = on-resistance.=20

=20
Figure 4. At +5V supply voltage, = later-generation=20 analog switches have lower = on-resistance.

When=20 selecting switches for single-supply systems, try to = choose=20 from those intended for single-supply use. Such = devices save=20 one pin, because they do not require separate V- and = ground=20 pins. As a result, this economy of pins enables a=20 single-pole/double-throw (SPDT) switch to fit into a = miniscule=20 6-pin SOT23 package. Similarly, low-voltage = dual-supply=20 applications call for dual-supply switches. These = switches=20 require a V- pin in addition to the ground pin, and = typically=20 specify a logic interface with standard CMOS and TTL=20 levels. The SPST MAX4529, for example, is also = available in a=20 6-pin SOT23 package.

Many high-performance = analog=20 systems still rely on higher-level bipolar supplies = such as=20 =C2=B115V or =C2=B112V. The interface to these = voltages requires an=20 additional supply pin commonly labeled V_L = (shown in=20 the MAX318 data=20 sheet). The V_L supply connects to the = system logic=20 voltage, which is usually 5V or 3.3V. Having the input = logic=20 signals referenced to the actual logic levels = increases the=20 noise margin and prevents excessive power=20 dissipation.

Often misunderstood is the = analog-switch=20 concept pertaining to input logic levels and their = effect on=20 supply current. If the logic inputs are at ground or=20 V_CC (or V_L when available), = analog=20 switches have essentially no supply current. Applying = TTL=20 levels to a 5V switch, however, can cause the supply = current=20 to increase more than 1000 times. To avoid unnecessary = power=20 consumption, you should avoid TTL levels, which are = simply a=20 legacy of the 1980s.

Signal Handling

Figure 3 also shows the value = of=20 R_ON versus signal voltage. These curves = fall within=20 the specified range of supply voltage, because analog = switches=20 can only handle analog-signal levels between the = supply=20 voltages. Under- or overvoltage inputs can permanently = damage=20 an protected switch by producing uncontrolled currents = through=20 internal diode=20 networks. Normally, these diodes protect the switch = against=20 short-duration electrostatic=20 discharge (ESD) as high as =C2=B12kV. =

R_ON=20 for a typical CMOS analog switch causes a linear = reduction of=20 signal voltage that is proportional to current passing = through=20 the switch. This might not be a disadvantage for = modest levels=20 of current or if the design accounts for = R_ON=20 effects. However, if you accept a certain level of=20 R_ON, then channel matching and = R_ON=20 flatness can interest you. Channel matching describes = the=20 variation of R_ON for the channels of one = device;=20 R_ON flatness describes the variation of=20 R_ON versus signal range for a single = channel.=20 Typical values for these parameters are 2=CE=A9 to = 5=CE=A9, and only=20 0.5=CE=A9 maximum for very low R_ON switches = (MAX4601,=20 for instance). The smaller the ratio of=20 matching/R_ON or flatness/R_ON is, = the=20 more accurate the switch.

In most applications, = you can=20 avoid excessive switch current by modifying the = circuit=20 design. To change the gain of an op=20 amp by switching between different feedback = resistances,=20 for example, choose a configuration that places the = switch in=20 series with a high-impedance input (Figure 5a). = Because=20 switch currents are insignificant, you can ignore the = value of=20 R_ON and its temperature coefficient. Switch = current=20 in the alternative design (Figure 5b) can be=20 substantial, because it depends on the output=20 voltage.

=20
Figure 5. Gain-control circuits are good (a) or = bad (b)=20 depending on the amount of current through the=20 switch.

Break-Before-Make

Turn-on and turn-off times=20 (t_ON and t_OFF) for most analog = switches=20 vary from below 60ns to as high as 1=C2=B5s. For = Maxim's=20 "clickless" audio switches, t_ON and = t_OFF=20 are in the millisecond range to eliminate the audible = clicks=20 otherwise present when switching audio signals. The = relative=20 magnitudes are also important: t_ON >=20 t_OFF yields break-before-make=20 action, and t_OFF > t_ON yields = make-before-break.=20 This distinction is critical for some=20 applications.

Figure 5a shows that you must = take care=20 in switching between the two gains. One switch is = normally=20 closed in a typical make-before-break application. In = changing=20 gain you must avoid opening both switches at once; = that is,=20 the second switch must close before the first switch = opens.=20 Otherwise, the op amp applies open-loop gain and = drives its=20 output to the rails. The opposite configuration=20 (break-before-make) is also useful in switching among=20 different input signals to a single op amp. To avoid = short=20 circuits between the input channels, a given = connection must=20 be switched off before the next one is switched=20 on.

When a changing signal level modulates the=20 on-resistance, causing a variation in the insertion = loss,=20 analog switches generate total=20 harmonic distortion (THD). Consider a 100=CE=A9 = switch with 10=CE=A9=20 R_ON flatness, for example. Loading this = switch with=20 a 600=CE=A9 termination produces 0.24% of THD. = Consequently, for=20 low THD you should avoid loading the output of an = analog=20 switch.

Charge-Injection Effects

As mentioned above, = low=20 R_ON is not necessary in all applications. = Lower=20 R_ON requires greater chip area. The result = is a=20 greater input capacitance whose charge and discharge = currents=20 dissipate more power in every switching cycle. Based = on the=20 time constant t =3D RC, this charging time depends on = load=20 resistance (R) and capacitance (C). It normally lasts = a few=20 tens of nanoseconds, but low-R_ON switches = have=20 longer-duration on and off periods. = High-R_ON=20 switches are faster.

Maxim offers both types of = switches, each with the same pinout in the same = miniature=20 SOT23 package. The MAX4501 and the MAX4502 specify = higher=20 on-resistance but shorter on/off times. The MAX4514 = and the=20 MAX4515 have lower on-resistance but longer switching = times.=20 Another negative consequence of low on-resistance can = be the=20 higher charge injection caused by higher levels of = capacitive=20 gate current. A certain amount of charge is added to = or=20 subtracted from the analog channel with every on or = off=20 transition of the switch (Figure 6). For = switches=20 connected to high-impedance outputs, this action can = cause=20 significant changes in the expected output signal. A = small=20 parasitic capacitor (C_L) with no other load = adds a=20 variation of =CE=94V_OUT, so charge = injection can be=20 calculated as Q =3D = =CE=94V_OUTC_L.

F= igure=20 6. Charge injection from the switch-control signal = causes a=20 voltage error at the analog output.

A = track/hold amplifier,=20 which maintains a constant analog output during = conversion by=20 an A/D=20 converter, offers a good example of this = (Figure=20 7). Closing S1 charges the small buffer capacitor = (C) to=20 the input voltage (V_S). The value of C is = only a=20 few picofarads, and V_S remains stored on C = when S1=20 opens. The held voltage (V_H) is applied to = the=20 buffer by closing S2 at the beginning of a conversion. = The=20 high-impedance buffer then maintains V_H = constant=20 over the ADC's conversion time. For short acquisition = times,=20 the track/hold's capacitor must be small and S1's=20 on-resistance must be low. On the other hand, charge = injection=20 can cause V_H to change by = =C2=B1=CE=94V_OUT (a few=20 millivolts), thereby affecting the accuracy of the = following=20 ADC.

F= igure=20 7. A typical track/hold function requires precise = control of=20 the analog switches.

Having reviewed these=20 fundamentals, we now focus on innovative switches for = special=20 applications.

T-Switches for Higher Frequencies

The T-switch = is=20 suitable for video and other frequencies above 10MHz. = It=20 consists of two analog switches in series, with a = third switch=20 connected between ground and their joining node. This=20 arrangement provides higher off-isolation than a = single=20 switch. The capacitive=20 crosstalk for a T-switch turned off typically = rises with=20 frequency due to the parasitic capacitances in = parallel with=20 each of the series switches (Figure 8). The = problem in=20 operating a high-frequency switch does not lie in = turning it=20 on, but in turning it off.

When the T-switch is = turned=20 on, S1 and S3 are closed and S2 is open. In the off = state, S1=20 and S3 are open and S2 is closed. In that case (the = off state)=20 the signal tries to couple through the off-capacitance = of the=20 series MOSFETs, but is shunted to ground by S3. If you = compare=20 the off isolation at 10MHz for a video T-switch = (MAX4545) and=20 a standard analog switch (MAX312), the result is = dramatic:=20 -80dB versus -36dB for the standard = switch.

F= igure=20 8. The T-switch configuration attenuates RF = frequencies that=20 couple through the stray capacitance between the = source and=20 the drain of an open (off) switch.

Smaller Packages

Other advantages for CMOS = analog=20 switches include small packages, such as the 6-pin = SOT23, and=20 no mechanical parts (unlike reed relays). Maxim offers = a small=20 video switch (MAX4529) as well as a standard, = low-voltage SPDT=20 switch (MAX4544). Both come in 6-pin SOT23 packages = and=20 operate from supply voltages in the 2.7V to 12V range. = The=20 MAX4544 is the smallest SPDT analog switch currently=20 available. See Table 2.

Table 2. = Small=20 packages
I_COM(OFF)/I_D(OFF)(nA=20 max) =

Part Number	Function	R_DS(ON)(=CE=A9 max)	R_ON = Flatness (=CE=A9=20 max)	t_ON/t_OFF (ns=20 max)	Charge Injection (pC = max)	Off-Isolation (dB = max)/Frequency (MHz)	Supply Voltage Range = (V)	Pin- Package
MAX4501/MAX4502	SPST NO/NC	250	1	-	75/50	10	-100/0.1	+2 to +12	5-SOT23-5\|8-DIP/SO
MAX4503/MAX4504	SPST NO/NC	250	1	-	150/100	10	-90/0.1	=C2=B11 to =C2=B16	5-SOT23-5\|8-DIP/SO
MAX4514/MAX4515	SPST NO/NC	20	1	3	150/100	10	-90/0.1	+2 to +12	5-SOT23-5\|8-DIP/SO
MAX4516/MAX4517	SPST NO/NC	20	1	4	100/150	20	-86/0.1	=C2=B11 to =C2=B16	5-/SOT23-5\|8-DIP/SO
MAX4529	SPST NC	70	1	10	75/75	10	-80/10	=C2=B12.7 to =C2=B16 or +2.7 to +12	6-SOT23-6\|8-DIP/SO//=C2=B5MAX
MAX4544	SPDT	60	0.1	6	100/75	5	-76/-90	+2.7 to +12	6-SOT23-6\|8-DIP/SO/=C2=B5MAX
MAX4707	1 SPDT NO	3	1	0.85	20/15	5	-82/1	+1.8 to +5.5	5-SC70 6-SC70
MAX4719	2 SPDT	20	0.5	1.2	80/40	18	-80/1	+1.8 to +5.5	10-=C2=B5MAX 12-USCP
MAX4723	2 SPDT NO/NC	4.5	0.5	1.2	80/40	18	-80/1	+1.8 to +5.5	8-=C2=B5MAX 9-USCP
MAX4730	1 SPDT	5.5	-	0.95	45/26	3	-67/1	+1.8 to +5.5	6-SC70
MAX4733	2 SPDT NO/NC	50	0.1	9	150/60	7.5	-72/1	+2 to +11	8-=C2=B5MAX 9-/USCP

As=20 mentioned earlier, Maxim offers many variations of = popular=20 analog switches like the CD4066, including a family of = low-cost quad analog switches = (MAX4610=E2=80=93MAX4612). The MAX4610=20 is a pin-compatible improvement over the = industry-standard=20 4066, but with lower supply voltage (as low as 2V) and = higher=20 accuracy: channel matching to within 4=CE=A9 maximum = and channel=20 flatness to within 18=CE=A9 maximum. This family of = parts offers=20 three switch configurations, and their lower = on-resistance=20 (< 100=CE=A9 at 5V) suits low-voltage applications. = A tiny=20 14-pin TSSOP=20 package (6.5 x 5.1 x 1.1mm =C2=B3 max) solves the = problem of board=20 space.

ESD-Protected Switches

Based on the success of = Maxim's=20 ESD-protected interface products, =C2=B115kV ESD=20 protection was added to some of the more recent = analog=20 switches (Table 3). Maxim now offers the first = switches=20 with =C2=B115kV ESD protection per IEC 1000-4-2 Level = 4 (the=20 highest level). All analog inputs are ESD-tested using = the Human=20 Body Model, as well as the Contact and Air-Gap = Discharge=20 methods specified in IEC 1000-4-2. The = MAX4551/MAX4552/MAX4553=20 switches are pin-compatible with many standard = quad-switch=20 families such as the DG201/211 and the MAX391 types. = To=20 augment standard multiplexer=20 families like the 74HC4051 and the MAX4581, Maxim also = released ESD-protected multiplexers. You no longer = need to use=20 costly TransZorbs=C2=AE to protect your analog=20 inputs.

Table 3. =C2=B115k ESD per IEC = 1000-4-2, in=20 16-pin DIP,=20 SO, and QSOP=20 packages
I_COM(OFF)/I_D(OFF)(nA=20 max)

Part Number	Function	R_DS(ON) (=CE=A9 max)	R_ON = Match (=CE=A9 max)	R_ON = Flatness (=CE=A9=20 max)	t_ON/t_OFF (ns=20 max)	Charge Injection (pC = typ)	100kHz = OFF-Isolation/Crosstalk (dB=20 typ)	Supply Voltage Range = (V)
MAX4551	4 SPST NO	120	=C2=B11	4	8	110/90	2	-90/-90	=C2=B12 to =C2=B16 or +2 to +12
MAX4552	4 SPST NC	120	=C2=B11	4	8	110/90	2	-90/-90	=C2=B12 to =C2=B16 or +2 to +12
MAX4553	4 SPST NO, NC	120	=C2=B11	4	8	110/90	2	-90/-90	=C2=B12 to =C2=B16 or +2 to +12
MAX4558	8 x 1 Mux	160	=C2=B11	6	8	150/120	2.4	-96/-93	=C2=B12 to =C2=B16 or +2 to +12
MAX4559	Dual 4 x 1 Mux	160	=C2=B11	6	8	150/120	2.4	-96/-93	=C2=B12 to =C2=B16 or +2 to +12
MAX4560	3 SPDT	160	=C2=B11	6	8	150/120	2.4	-96/-93	=C2=B12 to =C2=B16 or +2 to +12
MAX4569	1 SPST NO	70	=C2=B10.5	2	4	150/80	6	-75	=C2=B12 to =C2=B16 +2 to +12
MAX4577	2 SPST	70	=C2=B10.5	2	4	150/80	4	-75/90	=C2=B12 to =C2=B16 +2 to +12
MAX4620	4 SPST NO	70	=C2=B10.5	2	4	150/80	5	-75/90	=C2=B12 to =C2=B16 +2 to = +12

Fault-Protected Switches

As mentioned under = "Signal=20 Handling" above, the supply-voltage rails for an = analog switch=20 restrict the allowed range for input signal voltage. = Normally=20 this restriction is not a problem, but in some cases = the=20 supply voltage can be turned off with analog signals = still=20 present. That condition can permanently damage the = switch, as=20 can transients outside the normal range of the power = supply.=20 Maxim's fault-protected switches and multiplexers = guarantee overvoltage=20 protection of =C2=B125V and power-down protection = of =C2=B140V,=20 along with rail-to-rail signal handling and the low=20 on-resistance of a normal switch (Figure 9). = The input=20 pin, moreover, assumes a high impedance=20 during fault conditions regardless of the switch state = or load=20 resistance. Only nanoamperes of leakage current can = flow from=20 the source.

F= igure=20 9. This internal structure shows the special circuitry = in a=20 fault-protected analog switch.

If the = switch (P2 or=20 N2) is on, the COM output is clamped to the supply by = two=20 internal 'booster' FETs. Thus, the COM output remains = within=20 the supply rails and delivers a maximum of =C2=B113mA = depending on=20 the load, but without a significant current at the = NO/NC pin.=20 The fault-protected switches, MAX4511/MAX4512/MAX4513, = are=20 pin-compatible with the DG411=E2=80=93DG413 and = DG201/DG202/DG213=20 types (Table 4). Note that signals pass equally = well in=20 either direction through an ESD- and fault-protected = switch,=20 but these protections apply only to the input side.=20

Table 4. Fault protection with=20 rail-to-rail signal swings
I_COM(OFF)/I_D(OFF)
(nA=20 MAX) t_ON/t_OFF
(ns=20 max) =

Part Number	Function	R_DS(ON) (=CE=A9 max)	R_ON Match = (=CE=A9 max)	Overvoltage = Supplies ON/OFF=20 (V)	Charge Injection (pC = max)	Supply = Voltage Range(V)	Pin- Package
MAX4505	1 Line Protector	100	=C2=B10.5	-	-	=C2=B136/=C2=B140	-	=C2=B18 to =C2=B118 or +9 to +36	5-SOT\|8-=C2=B5MAX
MAX4506	3 Line Protector	100	=C2=B10.5	7	-	=C2=B136/=C2=B140	-	=C2=B18 to =C2=B118 or +9 to +36	8-DIP/SO/CERDIP
MAX4507	8 Line Protector	100	=C2=B10.5	7	-	=C2=B136/=C2=B140	-	=C2=B18 to =C2=B118 or +9 to +36	18-/DIP/SO/20-SSOP
MAX4508	8 x 1 Mux	400	=C2=B10.5	15	275/200	=C2=B125/=C2=B140	10	=C2=B14.5 to =C2=B120 or +9 to +36	16-DIP/SO
MAX4509	4 x 1 Mux	400	=C2=B10.5	15	275/200	=C2=B125/=C2=B140	10	=C2=B14.5 to =C2=B120 or +9 to +36	16-DIP/SO
MAX4511	4 SPST NO	160	=C2=B10.5	6	500/400	=C2=B136/=C2=B140	5	=C2=B18 to =C2=B118 or +9 to +36	16-DIP/SO/CERDIP
MAX4512	4 SPST NC	160	=C2=B10.5	6	500/400	=C2=B136/=C2=B140	5	=C2=B18 to =C2=B118 or +9 to +36	16/-DIP\|16/SO\|16/CERDIP
MAX4513	4 SPST NO, NC	160	=C2=B10.5	6	500/400	=C2=B136/=C2=B140	5	=C2=B18 to =C2=B118 or +9 to +36	16-DIP/SO/CERDIP
MAX4533	4 SPDT	175	=C2=B10.5	6	250/150	=C2=B125/=C2=B140	5	=C2=B14.5 to =C2=B120 or +9 to +36	20-Wide SO/SSOP
MAX4631	2 SPST NO	85	=C2=B10.5	6	150/100	=C2=B136/=C2=B140	10	=C2=B14.5 to =C2=B120 or +9 to +36	16-DIP/SO/CERDIP
MAX4632	2 SPDT	85	=C2=B10.5	6	150/100	=C2=B125/=C2=B140	10	=C2=B14.5 to =C2=B120 or +9 to +36	16-DIP/SO/CERDIP
MAX4633	2 DPST NO	85	=C2=B10.5	6	150/100	=C2=B136/=C2=B140	10	=C2=B14.5 to =C2=B120 or +9 to +36	16-DIP/SO/CERDIP
MAX4510	1 SPST NC	160	=C2=B10.5	-	500/175	=C2=B136/=C2=B140	5	+9 to +36 =C2=B14.5 to =C2=B120	6-/SOT23 8-=C2=B5MAX
MAX4520	2 SPDT NO	160	=C2=B10.5	-	500/175	=C2=B136/=C2=B140	5	+9 to +36 =C2=B14.5 to =C2=B120	6-SOT23 8-=C2=B5MAX
MAX4534	1 2:1MUX	275	=C2=B12	10	275/200	=C2=B125/=C2=B140	10	+9 to +36 =C2=B14.5 to =C2=B120	14-TSSOP/SO/DIP
MAX4535	2 2:1MUX	275	=C2=B12	10	275/200	=C2=B125/=C2=B140	10	+9 to +36 =C2=B14.5 to =C2=B120	14-TSSOP/SO/DIP
MAX4711	4 SPST NC	25	=C2=B10.5	1	125/80	=C2=B17/=C2=B112	25	+2.7 to +11 =C2=B12.7 to =C2=B15.5	8-=C2=B5MAX 9-UCSP

Force-Sense Switches

Maxim offers a family of = analog=20 switches with different switch types residing in the = same=20 package. The MAX4554/MAX4555/MAX4556 devices, for = instance,=20 are configured as force-sense switches for Kelvin = sensing in=20 automated test equipment (ATE). Each part contains=20 low-resistance high-current switches for forcing = current and=20 higher-resistance switches for sensing voltage or = switching=20 guard signals. On-resistance for the current switches = is only=20 6=CE=A9, and for the sensing switches is 60=CE=A9 at = =C2=B115V supply=20 voltages. The MAX4556 contains three SPDT switches = with=20 break-before-make action.

Typical force-sense=20 applications are found in high-accuracy systems and in = measurement systems that involve long distances = (Figure=20 10). For 4-wire measurements, two wires force a = voltage or=20 current to the load, and two other wires connected = directly to=20 the load sense the load voltage.

= Figure=20 10. With the 4-wire technique, two wires force and two = other=20 wires sense the measured = voltage.

Alternatively, a=20 2-wire system senses load voltage at the ends of the = force=20 wires opposite the load. Load voltage is lower than = the source=20 voltage, because the forcing voltage or current causes = a=20 voltage drop along the wires. Longer distance between = source=20 and load, larger load current, and higher conductor = resistance=20 all contribute for this degradation. The resulting = signal=20 reduction can be overcome by using a 4-wire technique = in which=20 the two additional voltage-sensing conductors carry = negligible=20 current.

Force-sense switches simplify many=20 applications, such as switching between one source and = two=20 loads in a 4-wire system. They are suitable for use in = high-accuracy measurement systems, such as = nanovoltmeters and=20 femtoammeters, and for 8- or 12-wire force-and-sense=20 measurements using the guard wires of triax cables. = For more=20 information, please see the MAX4554/MAX4555/MAX4556 = data=20 sheet.

Multiplexers

In addition to switches, Maxim = makes a=20 number of multiplexers (muxes). A mux is a special = version of=20 a switch in which two or more inputs are selectively = connected=20 to a single output. A mux can be as simple as an SPDT = switch=20 or come in 4:1, 8:1, 16:1, or even dual 4:1 and 8:1=20 combinations. The digital control for these higher = order muxes=20 is similar to a binary decoder with three digital = inputs=20 required to select the appropriate channel.

A=20 demultiplexer is basically a mux used backwards. That = is, one=20 input connects to two or more outputs based on the = decoded=20 address data.

There are, finally, cross-point = switches.=20 A cross-point switch is usually an M x N device, = whereby any=20 or all of M inputs may be connected to any or all of N = outputs=20 (and vice versa).

Calibration Multiplexers

Calibration = multiplexers=20 (cal-muxes) are used in precision ADCs and other=20 self-monitoring systems. They combine different = components in=20 one package: analog switches for generating accurate = voltage=20 ratios from an input reference voltage; internal = precision=20 resistor-dividers; and a multiplexer for selecting = between=20 different inputs. Maxim introduced this combination of = functions in a single package.

Two of these = devices=20 (MAX4539 and MAX4540) can balance two major errors = associated=20 with an ADC system: offset and gain=20 error. Using the internal precision = voltage-dividers,=20 these devices measure gain and offset in a few steps,=20 controlled trough the serial=20 interface of a microcontroller. The reference = ratios=20 15/4096 and 4081/4096 (with respect to the external = reference=20 voltage) are accurate to 15 bits. The ratios (5/8)(V+ = - V-)=20 and V+/2 are accurate to 8 bits.

The cal-mux = first=20 applies one-half the supply voltage to verify that = power is=20 present. The system then measures zero offset and gain = error,=20 and forms an equation to correct the subsequent = readings. Zero=20 input voltage, for example, should produce a digital = zero=20 output. The cal-mux calibrates for offset error by = applying a=20 very small input voltage of 15/4096 referred to=20 (V_EFHI - _REFLO). For a 12-bit = ADC with=20 4.096V reference, 15/4096 equals 15mV and also 15 = LSBs. The=20 digital output therefore should be binary = 000000001111. To=20 measure offset error, the microcontroller simply = records the=20 difference between binary 000000001111 and the ADC's = actual=20 output.

To measure gain error, the cal-mux = applies a=20 voltage of 4081/4096 referred to (V_REFHI -=20 V_REFLO). The microcontroller then records = the=20 difference between binary 111111110000 and the ADC's = digital=20 output. Knowing the ADC's offset and gain error, the = system=20 software constructs calibration factors that adjust = the=20 subsequent outputs to produce correct readings. The = cal-mux=20 then serves as a conventional multiplexer, but with = the=20 ability to recalibrate the system = periodically.

USB 2.0 Switches

A universal=20 serial bus (USB) is a high-speed interface for = handheld=20 devices to communicate with computers. Multiple USB = devices=20 can be connected to a computer, and analog switches = are used=20 to route the USB signal to different devices. The USB = 2.0 is a=20 high-speed signal that requires a high-bandwidth and=20 low-capacitance analog switch.

Maxim offers a = good=20 selection of USB 2.0-compliant switches ideal for USB = 2.0=20 high-speed applications. Table 5 shows a few = examples=20 of USB 2.0 switches.

Table 5. USB 2.0 = switches=20

Part	Functions	R_ON (O, max)	R_ON Match (O, = max)	t_ON/t_OFF (ns,=20 max)	I_COM(OFF) (nA, = max)	C_ON (pF, = typ)	C_OFF (pF, = typ)	Charge Injection (pC)	BW (MHz)	Supply Voltage Range = (V)
MAX4906F	2 SPDT	7	1.2	60/30	1000	6	2	5	1000	3.0 to 3.6
MAX4907F	2 SPST NO	7	1.2	60/30	1000	4	2	5	1000	3.0 to 3.6
MAX4906EF	2 SPDT	7	0.8	1.4/35	1000	10	9	20	500	2.7 to 3.6
MAX4899E	3 x 1 MUX	5	0.8	=E2=80=94	1000	15	10.2	25	425	2.7 to 3.6
MAX4899AE	4 x 1 MUX	5	0.8	=E2=80=94	1000	15	10.5	25	425	2.7 to 3.6

High-Voltage Switches

In ultrasound = applications,=20 high-voltage pulses (=C2=B1100V) are applied to = transducers to=20 generate ultrasonic waves. Analog switches are = required for=20 routing these high-voltage signals between the = transducers and=20 the main systems, so the switches must be able to = handle=20 high-voltage signals.

Maxim offers a good = selection of=20 high-voltage analog switches that are ideal for = ultrasound=20 medical applications. Table 6 shows a few=20 examples.

Table 6. High-voltage switches =

Part	Functions	V_SUPPLY (Single, = V)	V_SUPPLY (Single, = V)	V_SUPPLY (Dual, = =C2=B1V)	V_SUPPLY (Dual, = =C2=B1V)	BW (MHz)	I_L(OFF) (nA)	t_ON = (ns)	t_OFF = (ns)	C_ON = (pF)	C_OFF = (pF)
min	max	min	max
MAX4800A/MAX4802A	8 SPST NO	40	200	40	100	20	2000	5000	5000	36	11
MAX14800=E2=80=93MAX14803	16 SPST NO	40	200	40	100	20	2000	3500	3500	36	11

=C2=B5MAX=20 is a registered trademark of Maxim Integrated = Products,=20 Inc.

TRANSZORB = is a=20 registered trademark of Vishay General Semiconductor,=20 LLC.

UCSP is a trademark of Maxim Integrated = Products,=20 Inc.

Related parts =

MAX4066<= /TD>	Low-Cost, = Low-Voltage,=20 Quad, SPST, CMOS Analog Switch	Free=20 samples
MAX4514<= /TD>	Low-Voltage,=20 Low-On-Resistance, SPST, CMOS Analog = Switches	Free=20 samples
MAX4515<= /TD>	Low-Voltage,=20 Low-On-Resistance, SPST, CMOS Analog = Switches	Free=20 samples
MAX4529<= /TD>	Low-Voltage,=20 Bidirectional RF Video Switch	Free=20 samples
MAX4545<= /TD>	Quad/Dual, = Low-Voltage,=20 Bidirectional RF Video Switches	Free=20 samples
MAX4601<= /TD>	2.5=CE=A9, = Quad, SPST, CMOS=20 Analog Switches	Free=20 samples
MAX4610<= /TD>	Low-Voltage, = Quad, SPST=20 CMOS Analog Switches	Free=20 samples=20

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Download,=20 PDF format (143kB)
APP 638: Sep 03, = 2002=20
AN638, AN 638, = APP638,=20 Appnote638, Appnote 638=20 =