MIC2111B Datasheet, PDF(20/35 Page) Micrel Semiconductor – High-Performance, Multi-Mode, Step-Down Controller

English

English German Russian Spanish Italian Polish Chinese Japanese Korean French Portuguese	Language :

MIC2111B Datasheet, PDF (20/35 Pages) Micrel Semiconductor – High-Performance, Multi-Mode, Step-Down Controller

◁

Micrel, Inc.

Light Load Operation (DCM)

The MIC2111B supports pulse-skip mode for good light

efficiency. Connecting the MODE or SMOD# pin of the

power module to GND is required to enable the light-load

mode. To avoid discharging the output during light-load

mode, the power module zero current detector disables

the low-side FET once inductor current reaches zero. The

MIC2111B generates the next PWM signal based on

COMP voltage. This will cause discontinuous conduction

mode at the switch node as shown below.

MIC2111B

Figure 6. Light Load Operation (DCM)

Outside Audio Operation

Some systems require outside audio operation during

light-load mode. When the system load reduces during

light-load mode, the system will change from CCM to

DCM and, as the load reduces further, the switching

frequency reduces as well. If the effective switching

frequency reduces below a certain threshold, the

MIC2111B will enter outside audio mode, attempting to

maintain the effective switching frequency above the

audio band. For the outside audio mode to function, the

LS output of the MIC2111B must be connected to the

MODE pin of the DrMOS. While in this mode, if the

MIC2111B detects that the period between HS pulses is

longer than 32Âµs it forces LS a logic-1, which turns on the

low-side driver. This results in current flowing from the

output capacitor through the inductor and low-side

MOSFET. This can cause the output voltage to fall and

initiate a PWM cycle with HS going high and LS going

low.

Figure 7. Outside Audio Waveform

Output Overvoltage Protection (OVP)

The MIC2111B has a dedicated pin for overvoltage

protection (OVP). The OVP pin senses the output voltage

through a voltage divider. If this voltage is higher than the

reference voltage, the overvoltage protection engages

and FAULTb is pulled low.

This OVP function typically protects against open

feedback loop or VFB short-to-GND. This will protect the

costly load from being damaged by the DC/DC converter.

The OVP level can be programmed through a resistive

divider at the OVP pin as follows. Select R4 same as

lower feedback resistor. R1 can be calculated based

upon required OVP level as illustrated in Equation 1 and

Figure 8.

ï£®

ï£°ï£¯

VOUT â 0.6V

0.6V

ï£¹

ï£»ï£º

Eq. 1

Figure 8. OVP Programming

After the OVP fault is triggered, the system will be shut

down and latched off. It is required to cycle either VCC or

EN for enabling the converter.

October 13, 2015

Revision 2.1

▷