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1) Load resistance

ELM842B is designed for low power consumption applications; hence, the output source current is only

90μA (Typ. at Vdd=1.5V). As a result, ELM842B is not able to maintain output voltage swing when trying

to drive small load resistance. Considering this, load and feedback resistance for ELM842B should be

selected carefully.

ELM recommends the following operating temperature range.

< Power supply voltage >

< total resistance value of load/feedback resistor >

Vdd≤5.5V

:

R≥250kΩ

Vdd≤3.6V

:

R≥200kΩ

Vdd≤1.8V

:

R≥150kΩ

ELM842B is designed to be most suitable for single power source; therefore, ELM842B is able to share

power supply with logic circuit one. Meanwhile, ELM842B can also operate from double power sources .To

protect power supplies of ELM842B and logic circuit from noise, please separate wire from power supply

and use decoupling (bypass) capacitor. Using the capacitor can improve PSRR characteristics, especially on

10kHz to 100kHz or more.

When OP-AMP circuit is used with feedback resistor, oscillation may happen in the circuit with loop-gain

like unity gain follower.

a) When large feedback resistance is used, the phase margin is decreased by its combination with the

parasitic capacitance of the input part of OP-AMP. In this situation, please connect small capacitor parallelly

with feedback resistor as shown in fig-1.

b) For capacitive load, external resistor in series connection will be effective as shown in fig-2.

c) Being used as an unity gain follow, ELM842B is able to drive capacitive load of 100pF directly without

oscillation.

ELM842B is able to maintain operation when supply voltage is below 1.2V (Vdd≥1.2V) since all input

voltage is acceptable within the range of power supply voltage. However, AC characteristics will become

weak under this situation because of the decrease of bias current in the IC. For further information, please

contact ELM.

■Note

2) Operation from single power source

3) Feedback

4) Operation at Vdd<1.2V

a) fig-1

b) fig-2

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