HM1535 datasheet(4/7 Pages) HMSEMI

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OPERATION

The

HM1535 uses a fixed frequency,

peak current mode boost regulator

architecture to regulate voltage at the

feedback pin. The operation of the

HM1535 can be understood by referring

to the block diagram of Figure 3. At the

start of each oscillator cycle the

MOSFET is turned on through the control

circuitry. To prevent sub-harmonic

oscillations at duty cycles greater than 50

percent, a stabilizing ramp is added to

the output of the current sense amplifier

and the result is fed into the negative

input of the PWM comparator. When this

voltage equals The output voltage of the

error amplifier the power MOSFET is

turned off. The voltage at the output of

the error amplifier is an amplified version

of the difference between the 0.6V band

gap reference voltage and the feedback

voltage. In this way the peak current

level keeps the output in regulation. If the

feedback voltage starts to drop, the

output of the error amplifier increases.

These results in more current to flow

through the power MOSFET, thus

increasing the power delivered to the

output. The

HM1535 has internal soft

start to limit the amount of input current

at startup and to also limit the amount of

overshoot on the output.

Figure 3. Functional Block Diagram

HM1535 Datasheet(PDF) 4 Page - Shenzhen Huazhimei Semiconductor Co., Ltd