AN8032 データシートの表示（PDF） - Panasonic Corporation

部品番号

コンポーネント説明

メーカー

AN8032

Active filter control IC

Panasonic Corporation 

Voltage Regulators

AN8032

s Application Notes (continued)

[2] Operation descriptions (continued)

1. Normal control (continued)

2) Control outline description (Refer to figure 2 and figure 3.) (continued)

(8) Switching device turn-on

By resonance, the turn-on signal is sent to the switching device, timed with the sub-coil voltage when

it swings from high to low.

(9) Continuation of operation

When the switching device is turned on, current flows in the inductor so that the above operation is

repeated.

<Summary>

• When the excitation energy of inductor is lost and the free resonance is started, the switching device turns on.

• The switching device will turn off when the following two elements cross each other: The product of the input

voltage (EIN) and output one (EOUT) of the chopper circuit, and the switching device current.

• The fluctuation of input voltage and load current is controlled by changing the peak value height of switching

device current.

• The purposes of mixing two signals by using the multiplier are:

 to stabilize the control system

 to reduce the number of components required

3) Description of each function

(1) VB

• Function

It detects the discharge of the excitation energy of the inductor (reset operation) and turns on the power

MOSFET at the next cycle.

• Method

When the inductor is reset, the sub-coil provided on the inductor (bias winding) starts free resonance.

It is difficult from the view point of withstanding voltage to input this voltage directly to the IC. For this

reason, it is input to the VB terminal through resistor.

• Function of upper limit voltage clamper

It prevents the damage when the VB terminal voltage exceeds the withstanding voltage.

Function of lower limit voltage clamper

It prevents the malfunction when the VB terminal voltage swings to negative voltage: generally, in the

case of monolithic IC, malfunction (such as latch-up) occurs when the terminal voltage decreases to a value

below -VBE and the parasitic device is activated.

• IC inside

The VB terminal voltage is input to the comparator with hysteresis inside the IC. For this reason, if the

VB terminal voltage is under the threshold value, the power MOSFET is turned on.

However, if the off signal has been given to the power MOSFET by the overvoltage protection func-

tion, this function precedes the former.

Power MOSFET

OFF

ON

OFF

VB terminal input voltage

VBTH

(1.5 V typ.)

0V

Figure 4. VB terminal description

9

Share Link: