New-Tech Europe Magazine | Feb 2017

input is grounded. Note for IB+, a negative value means the current flow out of the +IN terminal. For IOUT, a negative value means the current flow out of the –IN terminal. Taking ADA4077-2 with V+ absent as an example, V+ is clamped to the VIN voltage by an ESD diode. VIN is connected to V+ via an ESD clamp diode, so when VIN is 0 V, V+ is –0.846 V. Current flow path loop: as the red path shown in Figure 4, 0.7 mA current flows from GND (+IN) to V+. 1.6 mA current flows from GND (+IN) through an internal resistor, D5 and the feedback path between –IN and OUT, then the current flow into output terminal. Finally the two currents (0.7 mA and 1.6 mA) combine to flow to –15 V, and the combined current flows back to GND (+IN). Results are similar between the ADA4177-2 and ADA4077-2. Note that within the ADA4177-2, D1 is implemented by an emitter base of a lateral PNP transistor. The transistor routes the overvoltage current away from the V+ to the V–. The ADA4177 circuit in Figure 4 shows 9.1 mA current flow from V+ back to V– , and combined with 0.2 mA current in the feedback path, results in a 9.3 mA current flow to –15 V, then the current flows back to GND. No large currents are observed at the input pins and power pins for either the ADA4077-2 or the

Figure 2. ADA4077/ADA4177 simplified block diagram

Table 3. Internal Diode of an Op Amp

Table 4. ADA4077-2/ADA4177-2 Results with Floating Input

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