MIC2132 datasheet(24/48 Pages) MICROCHIP

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MIC2132

DS20006654B-page 24

 2022 Microchip Technology Inc. and its subsidiaries

FIGURE 4-9:

Resistance Network Used

with RNTC Resistor for Linearization and Fitting

the Temperature Coefficient of MOSFET RDSON.

In case a temperature-independent resistor sensing is

used, a simple temperature constant standard

resistance is used on the ILIM pin.

4.5.3

NEGATIVE CURRENT LIMIT

The MIC2132 supports a cycle-by-cycle negative

current limit. The absolute value of the negative

current-limiting threshold is 50% of the programmed

current limit. If the negative low-side MOSFET current

is going to trigger a negative current limit, the low-side

MOSFET will be turned off and allow current through its

body diode. During this time, the output voltage tends

to rise, because this protection limits the current to

discharge the output capacitor. In order to prevent a

huge reverse current over the short limit value, the

low-side FET turns on after 500 ns, maintaining

negative current at the programmed level.

4.5.4

PRECISION ENABLE (EN)

The precision Enable (EN) input is used to control the

regulator. The precision feature allows the simple

sequencing of multiple power supplies with a resistor

divider from another supply. Connecting this pin to

ground, or to a voltage lower than 1.2V (typical), will turn

off the regulator. In this state, the current drain from the

input supply is 25 µA (typical) at a 12V input voltage.

The EN input has an internal pull-up of about 6 µA.

Therefore, this pin can be left floating or pulled to a volt-

age greater than 1.2V (typical) to turn the regulator on.

The hysteresis on this input is about 65 mV (typical)

below the 1.2V (typical) threshold. When driving the

enable input, the voltage must never exceed the abso-

lute maximum specification for this pin. Although an

internal pull-up is provided on the EN pin, it is a good

practice to pull the input high when this feature is not

used, especially in noisy environments. This can be

done easily by connecting a high-value resistor (1 MΩ)

between the VIN and EN pins. The MIC2132 device

also incorporates an internal input Undervoltage Lock-

out (UVLO) feature. This prevents the regulator from

turning on when the input voltage is not high enough to

properly bias the internal circuitry. The rising threshold

is 4.3V (typical) while the falling threshold is 3.9V (typ-

ical). In some cases, these thresholds may be too low

to provide good system performance. The solution is to

use the EN input as an external programmable input

UVLO to disable the part when the input voltage falls

below a target lower threshold. This is often used to

prevent excessive battery discharge or early turn-on

during start-up. This method is also recommended to

prevent abnormal device operation in applications

where the input voltage falls below the minimum of 4.5V.

Figure 4-10 shows the connections to implement this

method of UVLO. Equation 4-17 and Equation 4-18

can be used to determine the correct resistor values.

EQUATION 4-17:

EQUATION 4-18:

Due to the 6 µA pull-up, the current in the divider must

be much higher than this. A value of 20 kΩ for RBOT is

a good first choice.

FIGURE 4-10:

External Programmable VIN

UVLO Connections.

Where:

RTOP = Top Resistor of the VIN Voltage Resistor

Divider

RBOT = Bottom Resistor of the VIN Voltage Resistor

Divider

VOFF = Target VIN Voltage Below which the

Regulator Turns Off

VENTH = Device Enable Upper Threshold Voltage

VENHYS = Enable Threshold Hysteresis

RTOP = RBOT ×

VOFF

VENTH – VENHYS

– 1









Where:

VOFF = Input Voltage where the Regulator Shuts Off

VON = Input Voltage where the Regulator Turns On

VENHYST = Enable Threshold Hysteresis

VENTH = Enable Upper Threshold Voltage

VON = VOFF × (

)

VENTH

VENTH – VENHYS

MIC2132

RBOT

VIN

RTOP

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