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KA7525B Datasheet(PDF) 11 Page - Fairchild Semiconductor |
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KA7525B Datasheet(HTML) 11 Page - Fairchild Semiconductor |
11 / 18 page KA7525B 11 The equation below describes the relationship between multiplier output and inputs. Vmo = K × Vm1 × (Vm2-Vref) K : Multiplier gain Vm1: Voltage at Pin 3 Vm2: Error amp output voltage Vmo: Multiplier output voltage Current Sense Comparator The current sense comparator RS latch configuration used ensures that only a single pulse appears at the drive output during a given cycle. MOSFET drain current is converted to voltage using an external sense resistor in series with the external power MOSFET. When sense voltage exceeds the threshold set by the multiplier output, the current sense comparator terminates the gate drive to the MOSFET and resets the PWM latch. The latch insures that the output remains in a low state after the MOS- FET drain current falls back to zero. The peak inductor current under normal operating conditions is controlled by the multiplier output, Vmo. Abnormal operating conditions occur during preconverter start-up at extremely high line or if output voltage sensing is lost. Under these conditions, the multiplier output and current sense threshold will be internally clamped to 1.24V. Therefore, the maximum peak switch current is limited to: Ipk(max) = 1.24V / Rsense Internal R,C filter has been included to attenuate any high frequency noise that may be present on the current waveform. These circuit block eliminate the need for an external RC filter otherwise required for proper operation of the circuit. + - + - + + Vref 2 3 1.24V Current Sense Comparator Error Amp. Vmo Vm1 Vm2 INV MULT EA OUT + - 1 Figure 3.1 Multiplier Block 4 CS LEB Delay(KA7525) 4 cs 1.24V Multiplier Output Rsense eliminated Low Pass Filter can be Figure 4.1 Current Sense Circuit + - RC filter |
Similar Part No. - KA7525B |
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Similar Description - KA7525B |
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