JAJSMF5 データシート

JAJSMF5B september 2022 – june 2023 TPS25990

PRODUCTION DATA

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）

RQP|26
- MPQF569A

サーマルパッド・メカニカル・データ

発注情報

8.3.4.3 Active Current Limiting During Start-Up

The TPS25990 responds to output overcurrent conditions during start-up by actively limiting the current. The device constantly senses the current flowing through the device (I_DEVICE) and provides an analog current output (I_ILIM) on the ILIM pin, which in turn produces a proportional voltage (V_ILIM) across the ILIM pin resistor (R_ILIM) as per Equation 7.

Equation 7.

V_{I L I M} = I_{D E V I C E} \times G_{I L I M} \times R_{I L I M}

Where G_ILIM is the current monitor gain (I_ILIM : I_DEVICE)

The overcurrent condition is detected by comparing this voltage against a threshold which is a scaled voltage (CLREF_SAT) derived from the reference voltage (V_IREF) on the IREF pin as presented in Equation 8.

Equation 8.

{C L R E F}_{S A T} = \frac{0.7 \times V_{I R E F}}{3}

The reference voltage (V_IREF) can be controlled in two ways, which sets the overcurrent protection threshold (I_LIM) accordingly.

The reference voltage (V_IREF) can be generated using internal DAC and can be changed by programming the non-volatile configuration memory or dynamically through PMBus® writes to the VIREF register.
It is also possible to drive the IREF pin from an external low impedance precision reference voltage source.

The active current limit (I_LIM) threshold during start-up can be calculated using Equation 9.

Equation 9.

I_{I L I M} = \frac{{C L R E F}_{S A T}}{G_{I L I M} \times R_{I L I M}}

When the load current during start-up exceeds I_LIM, the device tries to regulate and hold the load current at I_LIM.

During current regulation, the output voltage drops, resulting in increased device power dissipation across the FET. If the device internal temperature (T_J) exceeds the thermal shutdown threshold, the FET is turned off. After the part shuts down due to a TSD fault, it either stays latched off or restarts automatically after a delay based on the RETRY_CONFIG register setting. See Overtemperature protection section for more details on device response to overtemperature.

Note:

The active current limit block employs a foldback mechanism during start-up based on the output voltage (V_OUT). When V_OUT is below the foldback threshold (V_FB), the current limit threshold is further lowered.