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# LTC6404-1 maximum output swing

Hi,

What is the maximum output swing I can get without clipping with a 3.3V / GND asymetrical supply ? I found the datasheet confusing on this point.

I read on datasheet page 4 that minimum V_OUTCMR is 1.1V. Does it mean that I will get clipping if (V_OUT+ + V_OUT-) / 2 < 1.1V ?

You also specify on page 4 "Output Voltage Low, Either Output Pin" (see figure below). Its value is 140mV at 3V 5mA for instance. What does this mean ? Does it mean that I won't get clipping if OUT+ and OUT- single ended voltage are above 140mV ? Is this this characterisitc I should look to evaluate the maximum voltage swing of the op amp ?

To give you some context, I want to use the LTC6404 to drive a 1.8V differential ADC with an input span of 2Vpp, and a common-mode voltage of 0.95V. Currently, the LTC6404 use a 3.3V / -1.8V supply to be sure there is no clipping around ground. Each output of the opamp is swinging between 0.45V and 1.45V, which makes me think there is no clipping, because 0.45V is above 140mV. But, I think that the -1.8V rail is not necessary in the end and that I won't get clipping if I use ground instead. I just need you to clarify the datasheet to make sure of it.

Thank you,

Maxime

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• Hi Maxime.

What is the maximum output swing I can get without clipping with a 3.3V / GND asymetrical supply ? I found the datasheet confusing on this point.

Since the datasheet only specifies parameters for VS = 3V and 5V, where VS = V+ - V-, and the difference of your supply voltages is 3.3V, you may refer to the specifications for VS = 3V to approximate the maximum output voltage swing.

I read on datasheet page 4 that minimum V_OUTCMR is 1.1V. Does it mean that I will get clipping if (V_OUT+ + V_OUT-) / 2 < 1.1V ?

V_OUTCMR is the output DC or bias voltage, and will depend on your input to the VOCM pin and on VS. Again, the V_OUTCMR range given in the datasheet is for VS = 3V and 5V only.

You also specify on page 4 "Output Voltage Low, Either Output Pin" (see figure below). Its value is 140mV at 3V 5mA for instance. What does this mean ? Does it mean that I won't get clipping if OUT+ and OUT- single ended voltage are above 140mV ? Is this this characterisitc I should look to evaluate the maximum voltage swing of the op amp ?

The "Output Voltage Low, Either Output Pin" parameter is the output low level headroom voltage. See note 10 in the succeeding pages of the datasheet. You will notice that this headroom voltage increases as the current load increases. For VS = 3V and IL = 5mA, for instance, the minimum possible VOH would be V+ - 600mV and for VS = 3V and IL = -5mA, the maximum possible VOL will be V- + 260mV. The resulting values will define the minimum possible output voltage swing. Using the typical values will result in a higher VOH and lower VOL, hence larger output voltage swing.

To give you some context, I want to use the LTC6404 to drive a 1.8V differential ADC with an input span of 2Vpp, and a common-mode voltage of 0.95V. Currently, the LTC6404 use a 3.3V / -1.8V supply to be sure there is no clipping around ground. Each output of the opamp is swinging between 0.45V and 1.45V, which makes me think there is no clipping, because 0.45V is above 140mV. But, I think that the -1.8V rail is not necessary in the end and that I won't get clipping if I use ground instead. I just need you to clarify the datasheet to make sure of it.

Please give us the part number of the ADC you are using so we can recommend a better setup for you. Better yet, send us your schematic so we can evaluate further. We also want to know your VIN specs so we can confirm if clipping occurs in your setup.

Regards,
Shine

• ```Version 4
SHEET 1 880 680
WIRE 128 -176 0 -176
WIRE 400 -176 208 -176
WIRE -528 -112 -528 -128
WIRE -432 -112 -432 -128
WIRE -528 -80 -528 -112
WIRE -432 -80 -432 -112
WIRE 160 0 160 -48
WIRE 160 0 96 0
WIRE -528 32 -528 0
WIRE -432 32 -432 0
WIRE 96 32 96 0
WIRE 160 32 160 0
WIRE 400 80 400 -176
WIRE 400 80 352 80
WIRE 448 80 400 80
WIRE 480 80 448 80
WIRE -128 128 -416 128
WIRE 0 128 0 -176
WIRE 0 128 -48 128
WIRE 48 128 0 128
WIRE 480 144 480 80
WIRE -416 176 -416 128
WIRE 0 176 -16 176
WIRE 48 176 0 176
WIRE -416 224 -416 176
WIRE -128 224 -192 224
WIRE 0 224 -48 224
WIRE 48 224 0 224
WIRE 400 272 352 272
WIRE 448 272 400 272
WIRE 480 272 480 224
WIRE 480 272 448 272
WIRE -192 288 -192 224
WIRE -192 336 -192 288
WIRE 160 368 160 320
WIRE -416 480 -416 304
WIRE -192 480 -192 416
WIRE 0 480 0 224
WIRE 128 480 0 480
WIRE 400 480 400 272
WIRE 400 480 208 480
FLAG 160 368 0
FLAG 160 -48 Vcc
FLAG -528 32 0
FLAG -528 -112 Vcc
FLAG 0 176 Vcm
FLAG -432 32 0
FLAG -432 -112 Vcm
FLAG 448 272 Vout+
FLAG 448 80 Vout-
FLAG -192 480 0
FLAG -192 288 Voff
FLAG -416 480 0
FLAG -416 176 Vpix
SYMBOL Opamps\\LTC6404-1 176 176 R0
SYMATTR InstName U1
SYMBOL voltage -528 -96 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 3.3
SYMBOL res -32 208 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 499
SYMBOL res -32 112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 499
SYMBOL voltage -432 -96 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 0.95
SYMBOL res 224 464 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 499
SYMBOL res 224 -192 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 499
SYMBOL res 464 128 R0
SYMATTR InstName R5
SYMATTR Value 2k
SYMBOL voltage -192 320 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 2.15
SYMBOL voltage -416 208 R0
WINDOW 3 -218 108 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value SINE(2.15 1 1k)
SYMATTR InstName V4
TEXT -640 528 Left 2 !.tran 0 5m 0 10n
```

• ```Version 4
SHEET 1 880 680
WIRE 128 -176 0 -176
WIRE 400 -176 208 -176
WIRE -528 -112 -528 -128
WIRE -432 -112 -432 -128
WIRE -528 -80 -528 -112
WIRE -432 -80 -432 -112
WIRE 160 0 160 -48
WIRE 160 0 96 0
WIRE -528 32 -528 0
WIRE -432 32 -432 0
WIRE 96 32 96 0
WIRE 160 32 160 0
WIRE 400 80 400 -176
WIRE 400 80 352 80
WIRE 448 80 400 80
WIRE 480 80 448 80
WIRE -128 128 -416 128
WIRE 0 128 0 -176
WIRE 0 128 -48 128
WIRE 48 128 0 128
WIRE 480 144 480 80
WIRE -416 176 -416 128
WIRE 0 176 -16 176
WIRE 48 176 0 176
WIRE -416 224 -416 176
WIRE -128 224 -192 224
WIRE 0 224 -48 224
WIRE 48 224 0 224
WIRE 400 272 352 272
WIRE 448 272 400 272
WIRE 480 272 480 224
WIRE 480 272 448 272
WIRE -192 288 -192 224
WIRE -192 336 -192 288
WIRE 160 368 160 320
WIRE -416 480 -416 304
WIRE -192 480 -192 416
WIRE 0 480 0 224
WIRE 128 480 0 480
WIRE 400 480 400 272
WIRE 400 480 208 480
FLAG 160 368 0
FLAG 160 -48 Vcc
FLAG -528 32 0
FLAG -528 -112 Vcc
FLAG 0 176 Vcm
FLAG -432 32 0
FLAG -432 -112 Vcm
FLAG 448 272 Vout+
FLAG 448 80 Vout-
FLAG -192 480 0
FLAG -192 288 Voff
FLAG -416 480 0
FLAG -416 176 Vpix
SYMBOL Opamps\\LTC6404-1 176 176 R0
SYMATTR InstName U1
SYMBOL voltage -528 -96 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 3.3
SYMBOL res -32 208 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 499
SYMBOL res -32 112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 499
SYMBOL voltage -432 -96 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 0.95
SYMBOL res 224 464 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 499
SYMBOL res 224 -192 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R4
SYMATTR Value 499
SYMBOL res 464 128 R0
SYMATTR InstName R5
SYMATTR Value 2k
SYMBOL voltage -192 320 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 2.15
SYMBOL voltage -416 208 R0
WINDOW 3 -218 108 Left 2
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value SINE(2.15 1 1k)
SYMATTR InstName V4
TEXT -640 528 Left 2 !.tran 0 5m 0 10n
```

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