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AN8018SA Datasheet(Fiches technique) 13 Page - Panasonic Semiconductor

Numéro de pièce AN8018SA
Description  1.8-volt 2-channel step-up, step-down, or inverting DC-DC converter control IC
Télécharger  26 Pages
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Fabricant  PANASONIC [Panasonic Semiconductor]
Site Internet  http://www.panasonic.com/industrial/
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AN8018SA Datasheet(HTML) 13 Page - Panasonic Semiconductor

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13
Voltage Regulators
AN8018SA
s Application Notes (continued)
[4] Function descriptions
1. Reference voltage block
This block is composed of the band gap circuit, and outputs the temperature compensated 1.19 V reference
voltage. The reference voltage is stabilized when the supply voltage is 1.8 V or more. The reference voltage is also
used as the reference voltage for the error amplifier 2 block.
2. Triangular wave oscillation block
The sawtooth-waveform-like triangular wave having
a peak of approximately 0.7 V and a trough of approxi-
mately 0.2 V can be generated by connecting the timing
capacitor CT and resistor RT to the OSC terminal (pin 1).
The oscillation frequency can be freely set by the value of
CT and RT to be connected externally. The usable oscilla-
tion frequency is from 20 kHz to the maximum 1 MHz.
The triangular wave is connected with the inverting input
of PWM comparator for channel 1 side and the
noninverting input of PWM comparator for channel 2 side
within the IC inside. Rough calculation of oscillation fre-
quency can be calculated by the following equation.
fOSC ≈ −
1
≈ 0.8 ×
1
[Hz]
CT × RT × ln VOSCL
CT × RT
VOSCH
However, boosting charge time, over-shoot and under shoot quantities are not considered in the above equation.
And refer to the experimentally determined graph of the frequency characteristics provided in the main
characteristics section.
3. Error amplifier 1 block
The output voltage of DC-DC converter is detected by the PNP-transistor-input type error-amplifier and the
amplified signal is input to the PWM comparator.
Also, it is possible to perform the gain setting and the phase compensation arbitrarily by connecting a resistor
and a capacitor from the FB1 terminal (pin 5) to GND in series.
The output voltage VOUT1 can be set by making connection as shown in figure 2.
t1
t2
T
VOSCH ≈ 0.7 V
VOSCL ≈ 0.2 V
Figure 1. Triangular wave oscillation waveform
Boosting
charge
Discharging
FB2
R1
R2
5
To PWM
comparator input
Error amplifier 1
block
IN
+13
IN
−14
VREF
VOUT1 =
VREF
··
Figure 2. Connection method of error amplifier 1 block
Case of step-up output
R3
+ R4
R4
R3
R4
VOUT1
R2
R1
+ R2
FB2
R1
R2
5
To PWM
comparator input
Error amplifier 1
block
IN
+13
IN
−14
VREF
VOUT1
VOUT1 = − (VREF − VIN−1)
+ V
REF
·
Case of inverting output
R1
+ R2
R1
R3
R4
VIN−1 = VREF ·
R4
R3
+ R4
4. Error amplifier 2 block
The output voltage of DC-DC converter is detected by the NPN-transistor-input type error-amplifier and the
amplified signal is input to the PWM comparator. The internal reference voltage 1.19 V is given to the noninverting
input.


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