MP6005

– WIDE-INPUT, HIGH-EFFICIENCY FLYBACK AND FORWARD CONTROLLER

MP6005 Rev. 1.0

www.MonolithicPower.com

19

2/5/2021

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

© 2021 MPS. All Rights Reserved.

Minimum On Time

The

parasitic

transformer

capacitance

and

GATE signal create a current spike on the

SENSE resistor when the power MOSFET turns

on. The MP6005 includes a 250ns leading-edge

blanking period to avoid false termination of the

switching pulse. During this blanking period, the

CS comparator turns off and the gate driver

remains on.

Gate Driver

The MP6005 has a high-current gate driver for

the primary-side N-channel MOSFET. This

driver has strong driving capability and benefits

for

MOSFET

selection

by

allowing

the

MOSFET

’s VGS to be charged quickly. If QG is

low, then the switching speed should remain

low as well. It is recommended to use a series

resistor above 5Ω to reduce EMI.

The MP6005 has a SYNC driver pin that

controls the second switch. If SYNC is high, the

second switch turns off. If SYNC is low, the

second switch turns on. Figure 4 shows the

phase and dead time relationships between the

GATE and SYNC pins.

tD

tD

50%

50%

GATE

SYNC

Figure 5: GATE and SYNC Driver

Both GATE and SYNC maintain a low voltage if

UVLO or another protection mode has turned

off the IC.

Transformer Inductance

In PSR mode, the MP6005 samples VOUT during

the flyback time, and the secondary diode

conduct

time

with

minimum

peak

current

(controlled by 33mV minimum sense limit)

should be longer than 0.7µs. The transformer

inductance can be calculated with Equation (2):

33mV

R

x

0.7

μ.

x

N

N

x

)

V

+

(V

L

SENSE

S

P

DOF

OUT

PRI ≥

(2)

Where

LPRI

is

the

transformer

’s

primary

inductance, and VDOF is the output rectifier

diode

’s forward drop.

There is no inductance limit in SSR mode.

However, if the IC is designed to work in

continuous conduction mode (CCM), set the

peak current high to avoid triggering PSM,

which may lead to a larger VOUT ripple,

(particularly in SYNC mode forward topology).

Thermal Shutdown

Thermal shutdown prevents thermal runaway. If

the silicon die temperature exceeds its upper

threshold, the MP6005 turns off. Once the

temperature

returns

to

below

its

lower

threshold, thermal shutdown ends and the

device turns on again with the next new cycle.