M51995 Mitsubishi, M51995 Datasheet - Page 13

• Manufacturer Part Number: M51995
• Description: SWITCHING REGULATOR CONTROL
• Manufacturer: Mitsubishi

The start-up current is such low current level as typical 90µ
A,as shown in Fig.3,when the Vcc voltage is increased
from low level to start-up voltage Vcc
In this voltage range,only a few parts in this IC,which has the
function to make the output voltage low level,is alive and
Icc current is used to keep output low level.The large voltage
difference between Vcc
easy,because it takes rather long duration from Vcc
Vcc
The oscillation waveform is the triangle one.The ON-duration
of output pulse depends on the rising duration of the triangle
waveform and dead-time is decided by the falling duration.
The rising duration is determined by the product of external
resistor R
determined by the product of resistor R
(1)Oscillator operation when intermittent action
Fig.4 shows the equivalent charging and discharging circuit
diagram of oscillator when the current limiting circuit does not
operate.It means that intermittent action and OSC control circuit
does not operate.
The current flows through R
of 5.8V.C
current,when internal switch SW1 is switched to "charging
side".The rise rate of C
Start-up circuit section
Oscillator section
The maximum on duration is approximately given as
where V
~
where V
~
(STOP)
and OSC control circuit does not operate
R
(V
Fig.3 Circuit current vs.supply voltage
V
~
ON
~
Icco
Icc
T
OSCH
14mA
V
90µA
-
.
X C
OSCH
T
ON
F
OSCL
L
ON
-
is charged up by the same amplitude as R
ON
-V
and capacitor C
F
V
OSCL
~
(V/s) ................................................(1)
~
~
T
-
4.4V
2.0V
4.5V
ON
) X R
SUPPLY VOLTAGE Vcc(V)
(START)
F
ON
terminal is given as
X C
~
ON
F
Vcc
(STOP)
9.9V
and the falling duration is mainly
and Vcc
from the constant voltage source
F
(s) ........................(2)
(START)
~
Vcc
(START)
16.2V
(STOP)
OFF
and capacitor C
.
makes start-up
(START)
ON
to
F
.
(
13
/ 27 )
C
sixteenth (1/16) of R
when SW1,SW2 are switched to "discharge side".
where V
The cycle time of oscillation is given by the summation of
Equations 2 and 4.
The frequency including the dead-time is not influenced by the
temperature because of the built-in temperature compensating
circuit.
So fall rate of CF terminal is given as
The minimum off duration approximately is given as
~
~
F
is discharged by the summed-up of R
(V
R
Fig.5 OSC.waveform at normal condition (no-
V
V
V
V
R
~
~
OFF
T
OSCH
T
R
OSCH
OSCL
V
2.0V
V
-
R
Fig.4 Schematic diagram of charging and discharging
4.4V
OFF
OFF
-
T
OFF
OH
C
OL
ON
OFF
F
-
X C
operation of intermittent action and OSC.control
circuit)
OFF
-V
+
OSCL
F
SWITCHING REGULATOR CONTROL
control circuit for OSC.capacitor C
16 X R
~
MITSUBISHI (Dig./Ana. INTERFACE)
M51995
V
CF
+
T-ON
T-OFF
) X C
T
3.5V
-
16 X R
ON
ON
ON
current by the function of Q2,Q3 and Q4
F
V
T
-
ON
(s) .....................................(4)
ON
X C
F
M51995AP/FP
(V/s)
FROM
VF SIGNAL
Vz 4.2V
Q3
.....................(3)
OFF
~
1/16
current and one
Q4
Q2
Q1
F
DISCHARGING
SW2
CHARGING
SW1
SWITCHED BY
CHARGING AND
DISCHARGING
SIGNAL
5.8V