CR6221 View Datasheet(PDF) - Unspecified

Part Name

Description

Manufacturer

CR6221

Green-Power Current Mode PWM Power Switch

Unspecified 

CR622X

Green-Power Current Mode PWM Power Switch

spike at initial internal power MOSFET on

state due to snubber diode reverse recovery

and surge gate current of internal power

MOSFET so that the external RC filtering on

sense input is no longer needed. The current

limiting comparator is disabled and cannot turn

off the internal power MOSFET during the

blanking period. The PWM duty cycle is

determined by the current sense input voltage

and the FB input voltage.

Internal synchronized Slope Compensation

Built-in slope compensation circuit adds

voltage ramp onto the current sense input

voltage for PWM generation. This greatly

improves the close loop stability at CCM and

prevents the sub-harmonic oscillation and thus

reduces the output ripple voltage.

Drive

The internal power MOSFET in CR622X is

driven by a dedicated gate driver for power

switch control. Too weak the gate drive

strength results in higher conduction and

switch loss of MOSFET while too strong gate

drive results the compromise of EMI.

A good tradeoff is achieved through the built-in

totem pole gate design with right output

strength and dead time control. The low idle

loss and good EMI system design is easier to

achieve with this dedicated control scheme.

In addition to the gate drive control scheme

mentioned, the gate drive strength can also be

adjusted externally by a resistor connected

between VDD and VDDG, the falling edge of

the Drain output can be well controlled. It

provides great flexibility for system EMI

design.

Protection Controls

Good power supply system reliability is

achieved with its rich protection features

including Cycle-by-Cycle current limiting

(OCP); Over load Protection (OLP); Under

Voltage Lockout on VDD (UVLO); Over

voltage protection (OVP) and VDD clamp

function.

The OCP is line voltage compensated to

achieve constant output power limit over the

universal input voltage range.

At overload condition when FB input voltage

exceeds power limit threshold value for more

than TD_PL, control circuit reacts to shut down

the switcher .Switcher restarts when VDD

voltage drops below UVLO limit.

VDD is supplied by transformer auxiliary

winding output. When VDD ramp up to OVP

threshold voltage (28.5V), the output of

CR622X will be shut down, when VDD drops

below UVLO(ON) limit and Switcher enters

power on start-up sequence thereafter. when

VDD higher than VDD clamp threshold

voltage, the internal VDD clamp circuitry will

clamp VDD to 30V, and the output of

CR622X is shut down also.

Nov, 2009 V2.2

7/10

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