CR6853 查看數據表（PDF） - ChengduChip-RailTech

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CR6853

Novel Low Cost Green-Power PWM Controller

ChengduChip-RailTech 

CR6853

resistance is 100Kohm, the delay time

TOLP&SCP is between 33mS and 50mS. The

relationship between RI and TOLP&SCP

follows the below equation.

RI × 2

6 ×103

(mS )

< TOLP&SCP

<

RI × 3

6 ×103

(mS )

Over Temperature Protection

The CR6853 has a built-in temperature

sensing circuit to shut down PWM output

once the junction temperature exceeds

130°C. While PWM output is shut down,

VDD voltage will gradually drop to the UVLO

voltage, and VDD voltage will gradually

increase again. If the junction temperature is

still higher than 130°C, the PWM controller

will be shut down again. This situation will

continue until the temperature drops below

100°C. The PWM output will then be turned

back. The temperature hysteresis window

for the OTP circuit is 30°C.

pin voltage descends gradually. When VDD

reaches 12.7V, the GATE pin would operate

again, which the frequency is 22KHz and

the max. Duty cycle is 14%.

Leading-edge Blanking (LEB)

Each time the power MOSFET is

switched on, a turn-on spike will inevitably

occur at the Sense pin, which would disturb

the internal signal from the sampling of the

RSENSE. There is a 300nS leading edge

blanking time built in to avoid the effect of

the turn-on spike, and the power MOSFET

cannot be switched off during the moment.

So that the conventional external RC

filtering on sense input is no longer required.

Sense Fault Detect

Changing the resistance of Sense pin

could limit the maximal peak current of

power MOSFET. If the Sense pin is short

circuit to the ground and the CR6853 is

overload, the power MOSFET and

transformer is easy to be shattered. So, the

short circuit protection is built in the CR6853.

Every time to start up, the circuit would

detect the voltage of the Sense pin when the

start signal is send. If the voltage keeps

lower than 177mV, the circuit would be cut

off and restart in 1.2mS. But, when the

switch power is cut off, there could always

be a big noise on the ground, so to achieve

this function, it is strongly suggested that the

board on the ground of the sense pin must

be attention.

Anti Intermission Surge

When the power supplies change the

heavy load to light load immediately, there

could be tow phenomena caused by system

delay. They are output voltage overshot and

intermission surge. To avoid it, the anti

intermission surge is built in the CR6853. If it

occurs, the FB current is to increase rapidly,

the GATE would be cut off for a while, VDD

Over Voltage Protection (OVP)

There is a 25.6V over-voltage

protection circuit in the CR6853 to improve

the credibility and extend the life of the chip.

When the VDD voltage is over 25.6V, the

GATE pin is to shutdown immediately and

the VDD voltage is to descend rapidly.

GATE Driver & Soft Clamped

The CR6853’ output designs a totem

pole to drive a periphery power MOSFET.

The dead time is introduced to minimize the

transfixion current during the output

operating. The novel soft clamp technology

is introduced to protect the periphery power

MOSFET from breaking down and current

saturation of the Zener.

Dec, 2007 V1.1

Chengdu Chip-Rail Tech. Co., Ltd.

8/11

http://www.chiprail.com

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