Table 7-4. MODE Pin Selection (continued)

CURRENT LIMITS

SOFT-START TIME (ms)

40.2

Low

1

4

49.9

Low

2

0.5

60.4

Low

2

1

76.8

Low

2

2

102

Low

2

4

137

Low

4

0.5

174

Low

4

1

243

Low

4

2

412

Low

4

4

7.3.9 Power Good (PGOOD)

The PGOOD pin is an open-drain output requiring an external pullup resistor to output a high signal. Once the

FB pin is between 92% and 108% of the internal voltage reference, soft start is complete, and after a 256-µs

deglitch time, the PGOOD pin is de-asserted and the pin floats. A pullup resistor between the values of 10 kΩ

and 100 kΩ to a voltage source that is 5.5 V or less is recommended. PGOOD is in a defined state once the VIN

input voltage is greater than 1 V but with reduced current sinking capability. When the FB is lower than 84% or

greater than 116% of the nominal internal reference voltage, after a 8-µs deglitch time, the PGOOD pin is pulled

low. PGOOD is immediately pulled low if VIN falls below its UVLO, the EN pin is pulled low or the device enters

thermal shutdown.

7.3.10 Current Protection

The protects against overcurrent events by cycle-by-cycle current limiting both the high-side MOSFET and low-

side MOSFET. In an extended overcurrent condition, the device will enter hiccup. Different protections are active

during positive inductor current and negative inductor current conditions.

7.3.10.1 Positive Inductor Current Protection

The current is sensed in the high-side MOSFET while it is conducting after a short blanking time to allow noise to

settle. Whenever the high-side overcurrent threshold is exceeded, the high-side MOSFET is immediately turned

off and the low-side MOSFET is turned on. The high-side MOSFET does not turn back on until the current falls

below the low-side MOSFET overcurrent threshold. This effectively limits the peak current in the case of a short

circuit condition. If a high-side overcurrent is detected for 15 consecutive cycles, the device enters hiccup.

The current is also sensed in the low-side MOSFET while it is conducting after a short blanking time to allow

noise to settle. If the low-side overcurrent threshold is exceeded when the next incoming PWM signal is received

from the controller, the device skips processing that PWM pulse. The device does not turn the high-side

MOSFET on again until the low-side overcurrent threshold is no longer exceeded. If the low-side overcurrent

threshold remains exceeded for 15 consecutive cycles, the device enters hiccup. There are two separate

counters for the high-side and low-side overcurrent events. If the off-time is too short, the low-side overcurrent

may not trip. The low-side overcurrent will, however, begin tripping after the high-side peak overcurrent limit is hit

as hitting the peak current limit shortens the on-time and lengthens the off-time.

Both the high-side and low-side positive overcurrent thresholds are programmable using the MODE pin. Two

sets of thresholds are available ("High" and "Low"), which are summarized in Table 7-5. The values for these

thresholds are obtained using open-loop measurements with a DC current in order to accurately specify the

values. In real applications, the inductor current will ramp and the ramp rate will be a function of the voltage

current sense circuitry can result in slightly different values than specified. The current at which the high-side

overcurrent limit takes effect can be slightly higher than specified, and the current at which the low-side

overcurrent limit takes effect can be slightly lower than specified.

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TPS543320

SLUSEE1 – DECEMBER 2020

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