MP9989

– FAST TURN-OFF INTELLIGENT RECTIFIER

MP9989 Rev. 1.1

www.MonolithicPower.com

10

8/27/2020

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

© 2020 MPS. All Rights Reserved.

APPLICATION INFORMATION

Slew Rate Detection Function

In DCM operations, the demagnetizing ringing

may bring VDS below 0V. If VDS reaches the turn-

on threshold during the ringing, SR controllers

without the slew rate detection function may turn

on the MOSFET by mistake. This not only

increases power loss, but may also lead to

shoot-through if the primary side MOSFET is

turned on within the minimum on time.

Considering the slew rate of the ringing is always

much less than when the primary MOSFET is

completely turned off, this false turn-on situation

can be prevented by the slew rate detection

function. When the slew rate is less than the

threshold, the IC does not turn on the gate even

when VDS reaches the turn-on threshold. For

more details, see the Turn-On Phase section on

page 8.

External Resistor on SENSE

Over-voltage conditions may lead to damage to

the device, so there must be appropriate

application design to guarantee safe operation,

especially on the high voltage pin.

One common over-voltage condition is when the

body diode of the SR MOSFET is turned on, as

the forward voltage drop may exceed the

negative rating on the SENSE pin. In this case,

it is recommended to place an external resistor

between SENSE and the MOSFET drain. In

general, the resistance is recommended to be

about 100

Ω to 300Ω.

On the other hand, this resistor also cannot be

too large, because it may compromise the VDD

supply and slow down the slew rate on the VDS

detection. In general, it is not recommended to

use a resistor greater than 300

Ω, but for each

use case, it should be checked based on the

condition of VDD supply and the slew rate.

Typical System Implementations

Figure 3 and Figure 4 show the typical system IC

implementation in low-side rectification and high-

side rectification, respectively.

SENSE

VS

VDD

VD

MP9989

Figure 3: Low-Side Rectification

SENSE

VS

VDD

VD

MP9989

Figure 4: High-Side Rectification

Maximum Output Current

The allowed temperature rise of the MP9989

limits the maximum output current the device can

handle. The temperature rise is determined by its

own power loss. Generally, for a universal input

adapter the recommended rated output current

for MP9989 is 4A. For certain designs, the power

loss of the MP9989 can be calculated, so the

maximum output current can be deduced.

The power loss of the MP9989 can be separated

into

several

parts:

controller

consumption,

integrated MOSFET conduction loss, and so on.

If the MP9989 works in continuous conduction

mode (CCM), reverse-recovery loss of the

integrated MOSFET must also be considered.

Each part of the loss can be calculated based on

Equation (1), Equation (2), and Equation (3):



LOSS _ CONTROLLER

SENSE _ P

DD

P

V

I

(1)









S _ ON

t

LOSS _ SR _ CONDUCTION

SW

SR _ SD

SR _ SD

0

P

f

V

(t) I

(t)dt (2)

 



 

LOSS _ SR _ RR

DS

RR

F

SW

1

P

V

I

t

f

2

(3)

Where IDD is the current of the MP9989, and

VSENSE_P is the corresponding plateau voltage in

the SENSE pin when SR turns off. fSW is the SR

switching frequency, and tS_ON is the SR on

period, VSR_SD is the voltage drop from the SR,

and ISR_SD is the current flowing from the SR. IRR