Battery-powered products are where the abstract parameters of an op-amp turn into arithmetic that a product manager can check. Quiescent current, supply rejection and the biasing scheme together decide whether the product lasts a month or a year — and they are exactly the parameters that get ignored when a part is substituted on price alone.
Quiescent current: small numbers, real consequences
Quiescent current (IQ) is what the amplifier draws with no load and no signal. It is quoted per channel, which is worth remembering for dual and quad parts. Compare the practical cost across cell sizes:
| Increase in supply current | 1000 mAh cell | 100 mAh cell | 10 mAh coin cell |
|---|---|---|---|
| 1 µA | 0.9% per year | 8.8% per year | 88% per year |
| 10 µA | 8.8% per year | ~88% per year | weeks |
| 100 µA | ~88% per year | weeks | days |
The lesson is that a two-microamp difference between two otherwise similar amplifiers is noise in a mains-powered instrument and a product-defining decision in a battery sensor. Which means the substitution decision depends on the product, not on the amplifier.
Supply rejection: the specification that only shows up in production
PSRR describes how much supply disturbance is transferred to the output, and it is frequency dependent. It is high at DC and falls off, hitting a minimum around the amplifier's bandwidth. A design powered from a linear regulator looks impeccable; the same design on a buck converter picks up switching harmonics at the output, and the resulting error appears as a mysterious low-level tone in the data.
When you substitute, the PSRR curve is one of the few parameters that genuinely cannot be inferred from the headline numbers. Two parts with identical offset, bandwidth and noise can differ by 20 dB of rejection at 1 MHz, which is precisely the frequency where a 2 MHz switcher puts its second harmonic.
Single-supply biasing: where the hidden cost lives
With a single rail, every AC-coupled stage needs a bias point. Three common approaches, with different costs:
- Resistor divider with a bypass capacitor. Two resistors and a capacitor, cheap and quiet if the noise is filtered, but the impedance is in the signal path and the capacitor sets the low-frequency corner.
- Dedicated reference plus buffer. The cleanest, adds a part and its quiescent current, and needs care about the buffer's own stability with a capacitive bypass.
- Mid-supply from another channel. Attractive in quad packages, but it loads one channel and couples disturbances between channels.
Every one of these choices interacts with the amplifier's input bias current, common-mode range and output capability — which is why a "same pinout, same speed" replacement can quietly shift the DC operating point of the stage and cost more than the part it replaced.
How to cost a substitution on power
- Build the average current budget first, including duty cycle and settling time, then see whether the amplifier's IQ is a material fraction of it.
- Check IQ per channel and at your supply voltage, not at a headline typical value.
- Compare PSRR at your switching frequency, not at DC, if the rail comes from a converter.
- Re-check the bias scheme after a change of input bias current or common-mode range; a shifted operating point often costs more than the parts saved.
| Model | IQ class | Positioned for | Link |
|---|---|---|---|
| COS6001TR | Micro-power, single | Battery sensor nodes, always-on monitoring | COS6001TR |
| COS6002SR | Micro-power, dual | Two-channel low-power conditioning | COS6002SR |
| COS6042SR | Nano-power, dual | Coin-cell products where IQ is the design constraint | COS6042SR |
| COS9061TR | Micro-power, 16 V capable | Higher-voltage portable instruments | COS9061TR |
| COS2314SR | Micro-power, dual, wide supply | Mixed 3.3 V and higher-rail designs | COS2314SR |
Browse the range in amplifiers and data conversion. Send us the cell capacity, the duty cycle and the rail source, and we will narrow the list to parts whose power profile actually fits the product rather than the price target.
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About us & trademarks: JTDZ Tech (Shenzhen Jinteng Electronics Technology Co., Ltd.) is an independent distributor of electronic components. We are not an authorised distributor or representative of the manufacturers named in this article. Manufacturer and part names are used for indicative purposes only, to help identify the components discussed and the parts they are commonly compared with; all trademarks remain the property of their respective owners. Always verify specifications against the manufacturer's datasheet before design-in or purchase.
