an8015sh Panasonic Corporation of North America, an8015sh Datasheet - Page 10

• Manufacturer Part Number: an8015sh
• Description: Single-channel Step-down, Step-up, Or Inverting Use Dc-dc Converter Control Ic
• Manufacturer: Panasonic Corporation of North America

AN8015SH
10
[3] Function descriptions (continued)
[4] Triangular wave oscillation circuit
5. Low input voltage malfunction prevention circuit (U.V.L.O.)
6. PWM comparator block
7. Output block
1. Oscillation frequency setting method
Application Notes (continued)
voltage is low in the transient state of power on/off.
according to the supply voltage level. Until the supply voltage reaches 3.1 V during its rise time, it cuts off the the
output drive transistor, sets the dead-time at 100% and holds the S.C.P. terminal (pin 3) to low level. During the
fall time of the power supply voltage, it has hysteresis width of 200 mV and operates 2.9 V or less.
output transistor during the period when the triangular wave of CT terminal (pin 1) of noninverted input is lower
than any one of the following voltages : the voltage of the error amplifier output (pin 10) of the inverted input, S.C.P.
terminal (pin 3), and the voltage for dead-time which is fixed inside the IC.
However, when the power supply is turned on, the soft start is activated, which gradually extends on-period
according to the time constant determined by the capacitance of externally attached capacitor and the charge current.
The maximum duty ratio is fixed at approximately 90% by the voltage for dead-time.
GND. The breakdown voltage of collector output terminal (pin 5) is 34 V and it is possible to obtain up to 100 mA
output current.
I
the externally attached timing resistor R
value of the wave V
typical and 0.37 V typical respectively.
following formula;
O
from the external timing capacitor C
This circuit protects the system from destruction or deterioration due to control malfunction when the supply
The low input voltage malfunction prevention circuit detects the internal reference voltage which changes
The PWM comparator controls the on-period of the output pulse according to the input voltage. It turns on the
The S.C.P. terminal voltage is kept at 1.25 V in the state in which DC-DC converter output is stabilized.
The output drive transistor is of open-collector type output connected in darlington circuit of emitter common
The waveform of triangular wave oscillation is obtained by charging and discharging of the constant current
The peak value of the wave V
The oscillation frequency f
The output frequency f
f
whereas
because
f
OSC
OSC
1.66 C
t
1
+ t
1
I
V
O
2
CTH
CTL
1
T
2
are fixed at approximately 1.4 V
2 C
V
R
V
R
T
CTL
OUT
RT
T
T
is equal to f
OSC
0.83 V
2
(V
CTH
is obtained by the
I
O
CTH
0.5
R
T
and the trough
T
T
which is connected to CT terminal (pin 1). The constant current is set by
.
V
OSC
CHL
since it is PWM-controlled.
)
Figure 4. Triangular wave oscillation waveform
Charging Discharging
t
1
T
t
2
Voltage Regulators
V
V
CTH
CTL
0.37 V typ.
1.4 V typ.