How to Calculate E-Paper Power Consumption: A Practical Example

For battery-powered electronic devices, low power consumption is often a key design requirement. But when evaluating an E-paper display, simply looking at the highest or lowest current number in the datasheet does not tell the whole story.

An E-paper display may consume several milliwatts while updating an image, but spend almost the entire day in a low-power state. In such applications, energy consumption over time is often more important than instantaneous power consumption.

This article uses a real E-paper display specification as an example to show how to calculate daily energy consumption and, just as importantly, how to understand the trade-off between Typical Operating, Sleep Mode, and Deep Sleep Mode.

Power vs. Energy: What’s the Difference?

Before doing the calculation, it is important to distinguish between power and energy.

Power describes how much energy a device consumes at a particular moment. It is typically measured in watts (W) or milliwatts (mW).

Energy describes how much power is consumed over a period of time. For battery-powered systems, it is commonly expressed in watt-hours (Wh), milliwatt-hours (mWh), or micro-watt-hours (µWh).

The basic relationships are:

Power: P = V × I

Energy: E = P × t

where:

• P = Power
• V = Supply Voltage
• I = Current
• E = Energy
• t = Time

This distinction becomes particularly important for E-paper because the display can spend very different amounts of time in different operating modes.

1. Start with the E-Paper Electrical Specifications

Let’s take the following example from an E-paper display datasheet.

At a typical VCI supply voltage of 3.0 V, the datasheet specifies:

The datasheet also provides an important distinction between Sleep Mode and Deep Sleep Mode:

• Sleep Mode: RAM data is retained.
• Deep Sleep Mode: RAM data is not retained.

We will come back to this difference later.

2. Calculate Power in Each Mode

Let’s first look at the instantaneous power consumption.

Typical Operating Mode

The typical operating current is 2.6 mA at 3.0 V.

Using:

P = V × I

we get:

P = 3.0 V × 2.6 mA = 7.8 mW

So, the display consumes approximately 7.8 mW while operating.

Sleep Mode

The typical Sleep Mode current is 20 µA.

Therefore:

P = 3.0 V × 20 µA = 0.06 mW

So Sleep Mode reduces the power consumption from approximately 7.8 mW to 0.06 mW.

Deep Sleep Mode

The typical Deep Sleep current is only 1 µA.

Therefore: P = 3.0 V × 1 µA = 0.003 mW, or: 3 µW

This is an extremely low power level compared with the Typical Operating state.

At this point, we have: 7.8 mW → 0.06 mW → 0.003 mW

However, these numbers only describe power. To understand battery impact, we need to consider how long the display stays in each mode.

3. From Power to Daily Energy Consumption

Let’s consider a simple application scenario.

Assume the E-paper display:

• Updates the image 2 times per day
• Takes approximately 3 seconds per update
• Remains in Deep Sleep Mode for the rest of the day

The datasheet specifies an image update time of approximately 3 seconds at 25°C.

For this example, we will use those 3 seconds as the approximate active period for each update.

Total Active Time

Two updates per day means: 3 sec × 2 = 6 sec/day

Convert seconds to hours: 6 ÷ 3600 = 0.001667 hours/day

4. Energy Consumed During Active Operation

The display consumes approximately 7.8 mW during Typical Operating.

Therefore: E_active = P × t = 7.8 mW × 0.001667 h ≈ 0.013 mWh/day

So even though the instantaneous operating power is relatively high, the display only spends about six seconds per day in this state.

The resulting daily energy consumption is only about: 0.013 mWh/day

5. Energy Consumed During Deep Sleep

The remaining time is spent in Deep Sleep.

Total time in one day: 24 hours

Active time: 0.001667 hours

Therefore: Deep Sleep time = 24 − 0.001667 ≈ 23.9983 hours

The Deep Sleep power is approximately 0.003 mW.

Therefore: E_sleep = 0.003 mW × 23.9983 h ≈ 0.072 mWh/day

Notice something interesting here.

The Deep Sleep power is extremely small, but because the display remains in Deep Sleep for almost the entire day, the accumulated energy consumption is not negligible.

6. Calculate the Total Daily Energy

Now we can add the energy consumed in both states:

E_total = E_active + E_deep sleep ≈ 0.013 + 0.072 ≈ 0.085 mWh/day

So, under this specific example, the display consumes approximately: 0.085 mWh per day

The approximate energy contribution is:

This is one of the most important lessons from the calculation.

Although the display’s Typical Operating power is more than 2,000 times higher than its Deep Sleep power, the display spends almost all of its time sleeping.

As a result, Deep Sleep accounts for approximately 84.7% of the daily energy consumption in this example.

7. Why Sleep Mode and Deep Sleep Mode Matter

The calculation above assumes that the display uses Deep Sleep after each update.

But why not always use Deep Sleep?

The answer is related to RAM data retention.

Sleep Mode: RAM Data Retained

According to the datasheet, Sleep Mode retains the RAM data.

In this mode:

• DC/DC is off
• The clock is off
• There is no input load
• RAM data is retained

Because the display data remains in RAM, the system can potentially resume operation without retransmitting the entire image, depending on the system implementation.

This makes Sleep Mode useful when the display needs to wake up relatively frequently or when fast recovery is important.

Deep Sleep Mode: RAM Data Not Retained

In Deep Sleep Mode, the datasheet specifies:

RAM data not retain

This means that the previously stored display data is not retained while the device is in Deep Sleep.

After waking up, the display will typically need to be re-initialized and the required display data transferred again.

The benefit is much lower standby power:

Sleep: ~20 µA

versus

Deep Sleep: ~1 µA typ.

This creates a classic system-level trade-off:

Lower standby power comes at the cost of additional work during wake-up.

8. Which Mode Should You Use?

There is no single best operating mode for every E-paper application.

The right choice depends on how frequently the display needs to update.

If the display updates frequently

Sleep Mode may be a better choice because the RAM data is retained and the system can recover more quickly.

If the display updates only occasionally

Deep Sleep can be attractive because the extremely low standby current minimizes energy consumption during long idle periods.

For example, a label that updates once or twice per day may benefit significantly from Deep Sleep.

For a device that wakes up every few minutes, however, the additional initialization and image transfer associated with Deep Sleep may become more significant.

Therefore, the optimal solution should consider:

• Display update frequency
• Wake-up time
• MCU processing time
• Data transfer requirements
• Battery capacity
• Standby current
• Overall system energy consumption

9. Don’t Just Look at the Current Number

When reviewing an E-paper datasheet, it can be tempting to focus on a single number:

“This display only consumes 1 µA in Deep Sleep.”

That number is useful, but it does not tell us the whole story.

A better approach is to ask:

How long does the display stay in each operating mode?

A display that consumes 7.8 mW for a few seconds per day may contribute less to the total energy budget than a display consuming only a few microwatts for the remaining 24 hours.

This is why battery-life calculations should be based on energy over the complete operating cycle, rather than simply comparing instantaneous current.

10. The Engineering Takeaway

For low-power E-paper applications, two equations are particularly important:

Power = Voltage × Current

Energy = Power × Time

Power tells us how much the device consumes right now.

Energy tells us how much the device consumes over the actual operating period.

In our example, the E-paper display consumes approximately:

• 7.8 mW during Typical Operating
• 0.06 mW in Sleep Mode
• 0.003 mW in Deep Sleep

With only two 3-second updates per day, the estimated daily energy consumption is approximately: 0.085 mWh/day

And despite its extremely low instantaneous power, Deep Sleep contributes approximately 84.7% of the daily energy consumption because the display remains in that state for almost the entire day.

This leads to a broader design principle for battery-powered products:

When a device spends most of its life in a low-power state, optimizing standby current can have a greater impact on battery life than optimizing active current alone.

For E-paper systems in particular, however, the lowest-power mode is not always the best mode. Power consumption, wake-up behavior, RAM retention, and update frequency all need to be considered together.

Ultimately, good low-power design is not simply about finding the smallest current number in the datasheet. It is about understanding how power is used over time—and choosing the operating mode that best matches the application.

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