LMH6552: Schematic design

Hale Tan

Part Number: LMH6552

Hi team,

Could you help check the schematic as below? Inout AC=1.5V Vpp, DC=0V, power supply is ±5V, but the output voltage follows the positive voltage. For example, when the power supply is 5V, the output voltage is above 4V not attend to 5V, and when the power supply is 4V, the output voltage is above 3V not attend to 4V. And they tried to adjust the gain=1, and the output still follows the power supply.

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 284810 points

This device does not have rail-to-rail inputs or outputs. The guaranteed input common-mode voltage range is ±3.5 V, and the guaranteed output voltage range is ± 3.7 V.

The are fully-differential amplifiers with rail-to-rail outputs (mostly low-voltage devices for a single 5 V supply), but they are slower than the LMH6552.

0 Hale Tan over 1 year ago in reply to Clemens Ladisch

TI__Expert 3360 points

Thanks, Clemens.

But I'm sorry that I didn't understand what is the issue about this application. The input voltage is only about 1.5Vpp with 0V bias which is in the common mode voltage range. And why the guaranteed output voltage range is ± 3.7 V?

0 Clemens Ladisch over 1 year ago in reply to Hale Tan

Guru 284810 points

There is no problem with the input voltages.

The differential output voltage is just the difference of the two outputs. The absolute output voltage also has limits, and requires a headroom of 1.3 V to the supplies:

0 Hale Tan over 1 year ago in reply to Clemens Ladisch

TI__Expert 3360 points

Hi Clemens,

Do yo think that the 50mV ripple for V- has an influence on the output？

0 Sima Jalaleddine over 1 year ago in reply to Hale Tan

TI__Mastermind 25705 points

Hello Hale,

Is the customer still seeing an issue with output voltage saturating to max output voltage as Clemens showed in snippet? Is the input voltage a sin wave and at what frequency?

The ripple shouldn’t affect the output voltage as said above, but we do recommend adding decoupling capacitors as noted in layout sections of any of our high speed amplifiers.

Thank you,

Sima

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LMH6552: Schematic design