AN8049 Panasonic Semiconductor, AN8049 Datasheet - Page 15

• Manufacturer Part Number: AN8049
• Description: 1.8-volt 3-channel step-up/ step-down/ and polarity inverting DC-DC converter control IC
• Manufacturer: Panasonic Semiconductor

Voltage Regulators
[4] Function descriptions
1. Reference voltage block
2. Triangular wave generator
3. Error amplifier 1
Application Notes (continued)
f
OSC
temperature compensated to a precision of 1%. This reference voltage is stabilized when the supply voltage is 1.8
V or higher. This reference voltage is used by error amplifiers 1 and 2.
sawtooth with a peak of 0.7 V and a trough of 0.2 V
using a capacitor C
R
frequency can be set to an arbitrary value by selecting
appropriate values for the external capacitor and resis-
tor, C
in the range 20 kHz to 1 MHz. The triangular wave
signal is provided to the noninverting input of the PWM
comparator in each channel internally to the IC. Use
the formulas below for rough calculation of the oscilla-
tor frequency.
account. See the experimentally determined graph of the oscillator frequency vs. timing capacitance value pro-
vided in the main characteristics section.
that detects and amplifies the DC-DC converter output
voltage, and inputs that signal to a PWM comparator.
The 1.26 V internal reference voltage is applied to the
noninverting input. Arbitrary gain and phase compen-
sation can be set up by inserting a resistor and capacitor
in series between the FB1 pin (pin 22) and the IN 1 pin
(pin 21). The output voltage V
circuit shown in the figure.
T
connected to the OSC pin (pin 15). The oscillator
This circuit is composed of a band gap circuit, and outputs a 1.26 V (typical) reference voltage that is
This circuit generates a triangular wave like a
Note, however, that the above formulas do not take the rapid charge time, overshoot, and undershoot into
This circuit is an npn-transistor input error amplifier
T
and R
C
T
T
R
. This IC can use an oscillator frequency
T
1
T
ln
(for the time constant) and resistor
V
V
OSCL
OSCH
OUT1
0.8
can be set using the
C
T
1
R
T
(Hz)
Rapid charge
R1
R2
V
OUT1
Figure 2. Connection method of error amplifier 1
Figure 1. Triangular oscillator waveform
V
t
1
OUT1
FB1
IN 1
(Step-up output)
22
21
1.26
Error
amplifier 1
Discharge
T
t
2
1.26 V
R
1
R
2
R
2
AN8049FHN
To the PWM
comparator input
V
V
OSCH
OSCL
0.7 V
0.2 V
15