11.1.1 Input Capacitor

It is recommended to place a capacitor (C_IN) between VIN and GND pins of TPS22963/64. This capacitor helps to limit the voltage drop on the input voltage supply when the switch turns ON into a discharged load capacitor. A 1-µF ceramic capacitor that is placed close to the IC pins is usually sufficient. Higher values of C_IN can be used to further reduce the voltage drop in high current applications.

11.1.2 Output Capacitor

It is recommended to place a capacitor (C_OUT) between VOUT and GND pins of TPS22963/64. This capacitor acts as a low pass filter along with the switch ON-resistance to remove any voltage glitches coming from the input voltage source. It is generally recommended to have C_IN greater than C_OUT so that once the switch is turned ON, C_OUT can charge up to V_IN without V_IN dropping significantly. A 0.1-µF ceramic capacitor that is placed close to the IC pins is usually sufficient.

11.1.3 Standby Power Reduction

Figure 38. Standby Power Reduction

Any end equipment that is being powered from the battery has a need to reduce current consumption in order to keep the battery charged for a longer time. TPS22963/64 helps to accomplish this by turning off the supply to the modules that are in standby state and hence significantly reduces the leakage current overhead of the standby modules.

11.1.4 Reverse Current Protection

The reverse current protection feature prevents the current to flow from VOUT to VIN when TPS22963/64 is disabled. This feature is particularly useful when the output of TPS22963/64 needs to be driven by another voltage source after TPS22963/64 is disabled (for example in a power multiplexer application). In order for this feature to work, TPS22963/64 has to be disabled and either of the following conditions shall be met: V_IN > 1 V or V_OUT > 1 V.

Figure 39 demonstrates the ideal behavior of reverse current protection circuit in TPS22963/64. After the device is disabled via the ON pin and VOUT is forced to an external voltage V_FORCE, a very small amount of current given by I_RC,VIN will flow from VOUT to VIN. This will prevent any extra current loading on the voltage source supplying the V_FORCE voltage.

I_VIN = Current through VIN pin.

V_SRC = Input voltage applied to the device.

V_FORCE = External voltage source forced at VOUT pin of the device.

I_OUT = Output load current.

Figure 39. Reverse Current Protection

11.1.5 Power Supply Sequencing Without a GPIO Input

Figure 40. Power Supply Sequencing Without a GPIO Input

In many end equipments, there is a need to power up various modules in a pre-determined manner. TPS22963/64 can solve the problem of power sequencing without adding any complexity to the overall system. Figure 40 shows the configuration required for powering up two modules in a fixed sequence. The output of the first load switch is tied to the enable of the second load switch, so when Module 1 is powered the second load switch is enabled and Module 2 is powered.

11.2.1 Design Requirements

11.2.2 Detailed Design Procedure

11.2.2.1 Managing Inrush Current

When the switch is enabled, the output capacitors must be charged up from 0 V to the set value (3.3 V in this example). This charge arrives in the form of inrush current. Inrush current can be calculated using the following equation:

Equation 1.

where

• C = output capacitance
• dV = output voltage
• dt = rise time

The TPS22963/64 offers a controlled rise time for minimizing inrush current. This device can be selected based upon the minimum acceptable rise time which can be calculated using the design requirements and the inrush current equation. An output capacitance of 4.7 µF will be used since the amound of inrush current increases with output capacitance:

Equation 2. 30 mA = 4.7 µF x 3.3 V / dt

Equation 3. dt = 517 µs

To ensure an inrush current of less than 30 mA, a device with a rise time greater than 517 µs must be used. The TPS22963/64 has a typical rise time of 715 µs at 3.3 V which meets the above design requirements.

11.2.3 Application Curves

Figure 42. TPS22963/64 Inrush Current with 4.7 µF Output Capacitor