-

+

2.5V

CF

RF

DPHOTO

CD

CCM

-2.5V

2.5V

VOUT

LMP7717

LMP7717, LMP7718

www.ti.com

SNOSAY7H – MARCH 2007 – REVISED MARCH 2013

Figure 60. LMP7715 Response Gain = +1

With no increase in power consumption the decompensated op amp offers faster speed than the compensated

equivalent part . These examples used RF = 2 kΩ. This value is high enough to be easily driven by the

LMP7717/LMP7718, yet small enough to minimize the effects from the parasitic capacitance of both the PCB and

the op amp.

NOTE

When using the LMP7717/LMP7718, proper high frequency PCB layout must be followed.

The GBW of these parts is 88 MHz, making the PCB layout significantly more critical than

when using the compensated counterparts which have a GBW of 17 MHz.

TRANSIMPEDANCE AMPLIFIER

An excellent application for either the LMP7717 or the LMP7718 is as a transimpedance amplifier. With a GBW

product of 88 MHz these parts are ideal for high speed data transmission by light. The circuit shown on the front

page of the datasheet is the circuit used to test the LMP7717/LMP7718 as transimpedance amplifiers. The only

change is that VB is tied to the VCC of the part, thus the direction of the diode is reversed from the circuit shown

on the front page.

Very high speed components were used in testing to check the limits of the LMP7717/LMP7718 in a

transimpedance configuration. The photodiode part number is PIN-HR040 from OSI Optoelectronics. The diode

capacitance for this part is only about 7 pF for the 2.5V bias used (VCC to virtual ground). The rise time for this

diode is 1 nsec. A laser diode was used for the light source. Laser diodes have on and off times under 5 nsec.

The speed of the selected optical components allowed an accurate evaluation of the LMP7717 as a

transimpedance amplifier. TIs evaluation board for decompensated op amps, PN 551013271-001 A, was used

and only minor modifications were necessary and no traces had to be cut.

Figure 61. Transimpedance Amplifier

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Product Folder Links: LMP7717 LMP7718