an8049sh Panasonic Corporation of North America, an8049sh Datasheet - Page 16

• Manufacturer Part Number: an8049sh
• Description: 1.8-volt 3-channel Step-up, Step-down, And Polarity Inverting Dc-dc Converter Control Ic
• Manufacturer: Panasonic Corporation of North America

AN8049SH
I Application Notes (continued)
16
[4] Function descriptions
1. Reference voltage block
2. Triangular wave generator
3. Error amplifier 1
4. Error amplifier 2
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 C
resistor R
the range 20 kHz to 1 MHz. The triangular wave signal
is provided to the noninverting input of the PWM com-
parator in each channel internally to the IC. Use the
formulas below for rough calculation of the oscillator
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 compensa-
tion can be set up by inserting a resistor and capacitor in
series between the FB1 pin (pin 24) and the IN−1 pin
(pin 23). The output voltage V
circuit shown in the figure.
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 compensa-
tion can be set up by inserting a resistor and capacitor in
series between the FB2 pin (pin 22) and the IN−2 pin
(pin 21). The output voltage V
circuit shown in the figure.
T
connected to the OSC1 pin (pin 17). 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
f
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
This circuit is an npn-transistor input error amplifier
OSC
≈ −
T
. This IC can use an oscillator frequency in
C
T
× R
T
(for the time constant) and resistor
T
× ln
1
V
V
OSCL
OSCH
OUT1
OUT2
≈ 0.8 ×
can be set using the
can be set using the
C
SDH00012BEB
T
× R
1
T
and
T
(Hz)
Rapid charge
R1
R2
R1
R2
Figure 2. Connection method of error amplifier 1
V
V
Figure 3. Connection method of error amplifier 2
OUT1
OUT2
Figure 1. Triangular oscillator waveform
t
V
1
V
OUT1
OUT2
IN−2
IN−1
FB1
FB2
= 1.26 ×
= 1.26 ×
(Step-up output)
(Step-up output)
24
23
22
21
Discharge
Error
amplifier1
Error
amplifier2
T
t
2
1.26 V
1.26 V
R
R
1
1
R
R
+ R
+ R
2
2
2
2
To the PWM
comparator input
To the PWM
comparator input
V
≈ 0.7 V
V
≈ 0.2 V
OSCH
OSCL