Start-up behavior is shown in Figure 3-6 through Figure 3-9. Note that in the dead battery scenario, there is no battery connected to VBAT, and VSYS starts from 0V. This is a less realistic scenario compared to the low battery scenario, where there is a battery simulator connected to VBAT and set to 3.6V, where VSYS starts from.

In Figure 3-6, there is a soft-start ramp from 0V to about 2V resulting from a pull up in the connected EV2400. This behavior is not relevant in a real-world application. Step 1 in VSYS is due to the buck converter turning on and VSYS ramping up to default 3.75V. Step 2 is when the battery is connected to the system, and VSYS rises about VBAT. Step 3 is when charge starts resulting in a small change in VSYS. This is similar to the behavior shown in Figure 3-8, where VSYS jumps from 3.6V to 3.75V and starts to rise to VBAT.

Figure 3-8 Start-Up With Charge Disabled, VBUS = 9V, VSYS = 3.75V, No Load, Low Battery Scenario

Figure 3-9 Start-Up With Charge Enabled, VBUS = 9V, VSYS = VBAT = 4.2V, No Load, Low Battery Scenario.