MP2113 – 1.5A, SYNCHRONOUS STEP-DOWN CONVERTER WITH DYNAMIC VOLTAGE CONTROL

MP2113 Rev. 1.0

www.MonolithicPower.com

9

4/4/2011

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Dropout Operation

The MP2113 allows the main switch to remain

on for more than one switching cycle to

increase the duty cycle when the input voltage

is dropping close to the output voltage. When

the duty cycle reaches 100%, the main switch is

held on continuously to deliver current to the

output up to the PFET current limit. In this case,

the output voltage becomes the input voltage

minus the voltage drop across the main switch

and the inductor.

Short Circuit Protection

When the output is shorted to ground, the

oscillator frequency is reduced to prevent the

inductor current from increasing beyond the

PFET current limit. The PFET current limit is

also reduced to lower the short circuit current.

The frequency and current limit will return to the

normal values once the short circuit condition is

removed and the feedback voltage approaches

0.6V.

Maximum Load Current

The MP2116 can operate down to 2.7V input

voltage; however the maximum load current

decreases at lower input due to a large IR drop

on the main switch and synchronous rectifier.

The slope compensation signal reduces the

peak inductor current as a function of the duty

cycle to prevent sub-harmonic oscillations at

duty cycles greater than 50%. Conversely, the

current limit increases as the duty cycle

decreases.

Asynchronous Mode Operation

To improve efficiency at light load condition, user

can set MP2113 to operate in asynchronous

mode.The maximum load current for this mode

is designed to be around 50mA.

Mode Switching

User can switch between the two operation

modes for MP2113 by toggling the CTRL input

pin on the fly. Bring CTRL high will put MP2113

in forced PWM mode and low will put MP2113 in

asynchronous mode. CTRL pin can also be used

to change the feedback resistor divider ratio,

through an open-drain output DRN pin. Bring

CTRL high will connect DRN to ground through a

low resistance (<100Ω) switch; Bring CTRL low

will put DRN pin to open circuit. User can simply

connect a third resistor between feedback pin

and DRN pin, to get a higher output level for

forced PWM mode and a lower level for

asynchronous mode. MP2113 is designed to

optimally ramp up and down the output voltage

when CTRL changes state. Typically it takes

about 10µs to ramp up the voltage and 30µs to

ramp down the voltage.

PGOOD Indicator

MP2113 provides an open-drain PGOOD

output that goes high after output level reaches

regulation

during

startup.

During

mode

switching where the output voltage level could

be changed, there is a 200us de-glitch time on

PGOOD to allow the output to settle to the

desired level, and to avoid false trigger.

PGOOD goes low if the output goes out of

regulation by ±10% and the de-glitch times out,

or when device enters shutdown.