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DS20005459B-page 19

MIC2125/6

4.4

Current Limit

sense the inductor current.

FIGURE 4-4:

MIC2125/6 Current-Limiting

Circuit

In each switching cycle of the MIC2125/6 converter, the

inductor current is sensed by monitoring the voltage

across the low-side MOSFET during the OFF period.

An internal current source of 36 µA generates a voltage

If the absolute value of the voltage drop across the low

event is triggered. Eight consecutive current limit

events triggers hiccup mode. The hiccup sequence,

including the soft-start, reduces the stress on the

switching FETs and protects the load and supply from

severe short conditions.

The current limit can be programmed by using

Equation 4-3.

EQUATION 4-3:

with temperature, it is recommended to add a 50%

current limiting due to increased MOSFET junction

temperature rise. It is also recommended to connect

the SW pin directly to the drain of the low-side

4.5

Negative Current Limit

(MIC2126 Only)

The MIC2126 implements negative current limit by

sensing the SW voltage when the low-side FET is off.

If the SW node voltage exceeds 12 mV typical, the

device turns off the low-side FET until the next ON-time

event is triggered. The negative current limit value is

given by Equation 4-4.

EQUATION 4-4:

4.6

MOSFET Gate Drive

The MIC2125/6 high-side drive circuit is designed to

switch an N-Channel MOSFET. Figure 4-1 shows a

bootstrap circuit, consisting of a PMOS switch and

MOSFET is on and the voltage on the SW pin is

approximately 0V. When the high-side MOSFET driver

MOSFET on. If the bias current of the high-side driver

is less than 10 mA, a 0.1 μF capacitor is sufficient to

= 10 mA × 3.33 μs/0.1 μF = 333 mV). A small resistor,

turn-on time of the high-side N-channel MOSFET.

4.7

Overvoltage Protection

The MIC2125/6 includes the OVP feature to protect the

load from overshoots due to input transients and output

short to a high voltage. When the overvoltage condition

is triggered, the converter turns off immediately to allow

the output voltage to discharge. The MIC2125/6 power

should be recycled to enable it again.

R

CL

I

CLIM



PP

0.5



+

 R

DS ON



V

OFFSET

–



I

CL

---------------------------------------------------------------------------------------------------------

=

Where:

Desired Current Limit

Inductor Current Peak-to-Peak

On-Resistance of Low-Side Power

MOSFET

Value is –4 mV per Table 1-1)

Current-Limit Source Current (Typical

Value is 36 µA, per Table 1-1)

I

NLIM

12mV

R

DS ON



--------------------

=

Where:

Negative Current Limit

On-Resistance of Low-Side Power

MOSFET