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ZHCSOF5A May 2022 – September 2022 TPS25985

PRODUCTION DATA

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机械数据 (封装 | 引脚)

RQP|26
- MPQF569A

散热焊盘机械数据 (封装 | 引脚)

订购信息

zhcsof5a_oa

8.3.4.3 Active Current Limiting During Start-Up

The TPS25985x responds to output overcurrent conditions during start-up by actively limiting the current. The device constantly senses the current flowing through each one (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 9.

Equation 9.

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 10.

Equation 10.

{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 start-up current limit threshold (I_LIM) accordingly.

In the standalone mode of operation, the internal current source interacts with the external IREF pin resistor (R_IREF) to generate the reference voltage as shown in Equation 11.
Equation 11. $V_{I R E F} = I_{I R E F} \times R_{I R E F}$
In a primary and secondary configuration, the primary eFuse or controller drives the voltage on the IREF pin to provide an external reference (V_IREF).

The active current limit (I_LIM) threshold during start-up can be calculated using Equation 12.

Equation 12.

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 (TSD), the FET is turned off. After the part shuts down due to a TSD fault, it either stays latched off (TPS259850 variants) or restarts automatically after a fixed delay (TPS259851 variants). 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.