HT2269 datasheet(9/13 Pages) HOTCHIP

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HT2269

9/13

Current Mode PWM Controller

www.hotchip.com.cn

Ver1.0

power dissipation in a switching mode power

supply is from switching loss on the MOSFET

transistor, the core loss of the transformer and the

loss on the snubber circuit. The magnitude of

power loss is in proportion to the number of

switching events within a fixed period of time.

Reducing switching events leads to the reduction

on the power loss and thus conserves the energy.

HT2269 self adjusts the switching mode

according to the loading condition. At from no load

to light/medium load condition, the FB input drops

below burst mode threshold level (1.8V). Device

enters Burst Mode control. The Gate drive output

switches only when VDD voltage drops below a

preset level and FB input is active to output an on

state. Otherwise the gate drive remains at off

stateto minimize the switching loss thus reduce

thestandby power consumption to the greatest

extend.

The nature of high frequency switching also

reduces the audio noise at any loading conditions.

Oscillator Operation

A resistor connected between RI and GND sets

the constant current source to charge/discharge

the internal cap and thus the PWM oscillator

frequency is determined.

The relationship between RI and switching

frequency follows the below equation within the

specified RI in Kohm range at nominal loading

operational condition.

Focs =

1560

RI(Kohm)

(Khz)

Current Sensing and Leading Edge

Blanking

Cycle-by-Cycle current limiting is offered in

HT2269 current mode PWM control. The switch

current is detected by a sense resistor into the

sense pin. An internal leading edge blanking

circuit chops off the sense voltage spike at initial

MOSFET on state due to snubber diode reverse

recovery so that the external RC filtering on

sense input is no longer required. The current

limit comparator is disabled and thus cannot turn

off the external MOSFET during the blanking

period. 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.

Over Temperature Protection

A NTC resistor in series with a regular resistor

should connect between RT and GND for

temperature sensing and protection. NTC resistor

value becomes lower when the ambient

temperature rises.

With the fixed internal current IRT flowing

through the resistors, the voltage at RT pin

becomes lower at high temperature. The internal

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