MP2145

– 5.5V, 6A, 1.2MHz, COT, BUCK SWITCHER

MP2145 Rev. 1.11

www.MonolithicPower.com

14

12/20/2016

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© 2016 MPS. All Rights Reserved.

Light-Load Operation

During

light

loads,

the

MP2145

uses

a

proprietary control scheme to save power and

improve efficiency: There is a zero current

cross circuit to detect if the inductor current

starts to reverse. LS-FET turns off immediately

when the inductor current starts to reverse and

trigger the ZCD in discontinuous conduction

mode (DCM) operation.

Considering the internal circuit propagation time,

the typical delay is 50ns. It means the inductor

current still fall after the ZCD is trigger in this

delay. If the inductor current falling slew rate is

low side MOSFET is turned off and inductor

current may be negative. This phenomena will

cause MP2145 can not enter DCM operation. If

the DCM mode is required, the off time of low

side MOSFET in CCM should be longer than

100ns. For example, Vin is 3.6V and Vo is 3.3V,

the off time in CCM is 70ns. It is difficult to enter

DCM at light load. And using smaller inductor

can improve it and make it enter DCM easily.

Enable

When the input voltage exceeds the under-

voltage

lockout

(UVLO)

threshold

—typically

2.55V

—the MP2145 can be enabled by pulling

the EN pin above 1.6V. Leaving EN pin floating

or grounded will disable the MP2145. There is

an internal 1MΩ resistor from the EN pin to

ground.

Mode

Selection

and

Analog

Voltage

Dynamic Regulation

MP2145 has programmable PWM and PFM

work mode. When MODE/VCON is more than

1.2V, MP2145 enters PWM mode. When

MODE/VCON is lower than 0.4V or floating,

MP2145 enters PFM mode. PFM mode can

achieve high efficiency by light-load operation.

PWM

mode

can

keep

constant

switch

frequency and smaller Vo ripple, but it has low

efficiency at light load.

Figure 5: Reference Voltage change with VCON

MP2145 can dynamic regulate output voltage

by MODE/VCON pin to meet some situation

need change output voltage directly. When

MOED/VCON pin get an appropriate voltage

value (from 0.6V to 1.1V), MP2145 will work

with PWM mode and internal reference voltage

changes smoothly to achieve a new output

voltage

without

changing

external

resistor

divider, as Figure 5. When VCON function is

enabled, set Ref voltage from 0.35V to 0.6V,

the accuracy is 3% typically. When set Ref

voltage from 0.1V to 0.35V, the accuracy is

10% typically. Detail Ref voltage calculation

formula such as below:

Ref(V)=0.985 VCON(V)-0.486



Soft-Start

The MP2145 has a built-in soft-start that ramps

up the output voltage at a constant slew rate

that avoids overshooting at startup. The soft-

start time is typically about 1.5ms.

Pre-Bias Startup

The MP2145 can start up with a pre-bias output

voltage. If the internal SS voltage is lower than

the FB voltage, the HS-FET and LS-FET

remain off until the SS voltage crosses the FB

voltage.