TPS1HC30-Q1
ZHCSP75A –JULY 2022 –REVISED DECEMBER 2022
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9.2.2.1 Dynamically Changing Current Limit
The current limit threshold can be changed dynamically by altering the resistance going from the current limit pin
to the ground of the device on the fly. This alteration allows the system to have a different current limit for start-
up, when there can be significant inrush current, and during normal operation. The way this is commonly done is
by putting two resistors in parallel on the ILIM pin and having a switch to enable or disable one of the resistors.
This set-up can be seen in 图 9-2. Alternatively, a digital potentiometer can be used to adjust the impedance on
the ILIM pin on the fly. Care must be taken so that the capacitance on the ILIM pin is below approximately 100
pF to keep the current regulation loop stable. The most common application where this feature is useful is
capacitive loads.
VBAT
VBB
Smart High Side Switch
EN
Gate Driver
KCL
KCL (RILIM1 + RILIM2
RILIM1 RILIM2
)
ILIM1
=
ILIM2
=
SW
RILIM
ILIM
Current Limiting
Circuit
(VBB – VOUT
RLOAD
)
INOM
=
VOUT
RILIM2
RILIM1
CLOAD
GND
RLOAD
ILIM = CLOAD x dVDS/dt
图9-2. Dynamic Changing Current Limit Setup
In a capacitive charging case, the initial current to charge the capacitor is the inrush current. Depending on the
system requirements, dynamically changing the current limit can help either charge up a capacitor faster or
charge up a larger capacitor. To allow a higher inrush level of current through in the beginning, the switch can be
closed making the current limit be according to the equation below.
ILIM2 = KCL(RILIM1 + RILIM2) / (RILIM1 × RILIM2
)
(16)
When the inrush event is over and the output voltage is charged up, the switch opens and the current limit is just
the RILIM1 equivalent level. This timing can be seen in 图9-3.
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