AN8014 Просмотр технического описания (PDF) - Panasonic Corporation
Номер в каталоге
Компоненты Описание
производитель
AN8014 Datasheet PDF : 18 Pages
| |||
AN8014S
Voltage regulators
s Application Notes (continued)
[1] Function descriptions (continued)
2. The triangular wave generator block (OSC)
The triangular wave which swings from approximately 1.32 V (upper limit value, VOSCH) to approximately 0.44
V (lower limit value, VOSCL) will be generated by connecting a timing capacitor CT and a resistor RT to the CT pin
(pin 3) and RT pin (pin 2) respectively. Oscillator frequency can be freely decided by the value of CT and RT
connected externally. The oscillator frequency fOSC is obtained by the following formula;
1
fOSC = t1 + t2
=
IO
2 × CT × (VCTH − VCHL)
IO =
1.7 ×
VRT
RT
= 1.7
×
0.4
RT
Because VCTH − VCTL = 0.88 V
1
fOSC ≈ 2.59 × CT × RT [Hz]
Example) An fOSC of approximately 215 kHz will be
obtained if CT is 120 pF and RT is 15 kΩ.
VCTH = 1.32 V (typ.)
t1
t2
Charging Discharging
VCTL = 0.44 V (typ.)
T
Figure 1. Triangular oscillation waveform
It is possible to use the circuit in the recommended operating range of 5 kHz to 500 kHz of the oscillator
frequency. As the AN8014S is used at increasingly higher frequencies, the amount of overshoot and undershoot
due to the operation delay in the triangular wave oscillator comparator increases, and discrepancies between the
values calculated as described previously and the actual values may occur.
The output source currents of the AN8014S's S.C.P. and DTC pins are determined by the timing resistor RT
which is externally connected to the RT pin. Therefore, note that this IC can not be used as an IC for slave when
the several ICs are operated in parallel synchronous mode.
3. Error amplifier block
Detecting and amplifying DC-DC converter output voltage, the error amplifier with PNP transistor input inputs
the signal to the PWM comparator.
Figure 2 shows the way to connect the error amplifier.
The common-mode input voltage range is − 0.1 V to + 0.8 V, and a voltage obtained by dividing the reference
voltage with built-in resistors is applied to the non-inverting input. Connecting the feedback resistor and the
capacitor between the error amplifier output pin (pin 8) and the inverting input pin (pin 7) allows the arbitrary gain
setting and the phase compensation.
Startup overshooting caused by feedback delays will be suppressed by setting the output source current and
output sink current to as high as 110 µA and 8 mA respectively.
The input voltage VIN+ and VIN− to the error amplifier are obtained from the following formulas.
VIN+ = VREF ×
R4
R3 + R4
VIN− = VOUT ×
R2
R1 + R2
1
VREF
R3
Error PWM comparator
IN+ 6 amp. CT
DTC
13
IN− 7
R4
8
RNF
FB
VOUT
R1
R2
CNF
Figure 2. Connection method of error amplifier
8
Share Link: 