MP163 datasheet(13/23 Pages) MPS

13 / 23 page

MP163 – 700V, NON-ISOLATED, OFFLINE REGULATOR WITH INTEGRATED LDO

MP163 Rev. 1.01

www.MonolithicPower.com

8/11/2017

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

OPERATION

The MP163 is a green-mode operation

regulator

. The peak current and the switching

frequency both decrease with a decreasing load.

As a result,

the MP163 offers excellent light-

load efficiency and improves overall average

efficiency.

The regulator also incorporates

multiple features and operates with a minimum

number of external components.

The MP163 acts as a fully integrated regulator

when used in

a buck topology (see the Typical

Application on page

2).

Start-Up and Under-Voltage Lockout (UVLO)

The internal high-voltage regulator self-supplies

the IC from DRAIN. When VCC reaches

VCCOFF, the IC starts switching, and the internal

high-voltage regulator turns off. The internal

high-voltage regulator turns on to charge the

external VCC capacitor when VCC falls below

VCCON. A small capacitor (in the low μF range)

maintains VCC and lowers the capacitor cost.

The IC stops switching when VCC drops b

elow

VCCstop.

Under fault conditions

(such as OLP, SCP, and

TSD

) the IC stops switching, and an internal

current source (~16μA) discharges the VCC

capacitor. The internal high-voltage regulator

will not charge the VCC capacitor until VCC

drops below VCCpro. The restart time can be

estimated using Equation (1):

pro

OFF

pro

restart

VCC

CCLATCH

regulator

VCC VCC

VCC













(1)

Soft Start (SS)

The IC stops operation when VCC drops b

elow

VCCstop. The IC begins operation when VCC

charges to VCCOFF. There is a soft-start

period whenever the chip starts operation.

Soft start prevents the inductor current from

overshooting by limiting the minimum off time.

The MP163 adopts a two-phase minimum off-

time limit soft start.

Each soft-start phase lasts

for 128 switching cycles. During soft start, the

off

-time limit shortens gradually from τminoff_SS1

to τminoff_SS2 and reaches τminoff (see Figure 2).

Figure 2: Minimum Off Time at Start-Up

Constant Voltage (CV) Operation

The MP163 regulates the output voltage by

monitoring the sampling capacitor (C3).

At the beginning of each cycle, the integrated

MOSFET turns on while the feedback voltage

drops below the 2.55V reference voltage, which

indicates

an insufficient output voltage. The

peak current limitation determines the on period.

After the on period elapses, the integrated

MOSFET turns off. The sampling capacitor (C3)

voltage is charged to the output voltage through

D3 when the freewheeling diode (D2) turns on.

This way, the sampling capacitor (C3) samples

and holds the output voltage for output

regulation. The sampling capacitor (C3) voltage

decreases when the inductor

(L1) current falls

below the output current. When the feedback

voltage falls below the 2.55V reference voltage,

a new switching cycle begins. Figure 3 shows

this operation in continuous conduction mode

(CCM).

MOSFET

Diode

Ipeak

VFB

2.55V

Figure 3: VFB vs. VO

Determine the output voltage with Equation

(2):





R1 R2

Vo 2.55V

(2)

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