M51995AP

Manufacturer Part NumberM51995AP
DescriptionSwitching regulator control
ManufacturerMITSUBISHI
M51995AP datasheet
 


1
2
3
4
5
6
7
8
9
10
11
Page 11
12
Page 12
13
Page 13
14
Page 14
15
Page 15
16
Page 16
17
Page 17
18
Page 18
19
Page 19
20
Page 20
21
22
23
24
25
26
27
Page 13/27:

Start-up circuit section

Download datasheet (462Kb)Embed
PrevNext

Start-up circuit section

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
(START)
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
and Vcc
(START)
(STOP)
easy,because it takes rather long duration from Vcc
Vcc
.
(STOP)
Icco
~
14mA
Icc
L
~
90µA
Vcc
Vcc
(STOP)
(START)
~
~
9.9V
16.2V
SUPPLY VOLTAGE Vcc(V)
Fig.3 Circuit current vs.supply voltage
Oscillator section
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
and capacitor C
and the falling duration is mainly
ON
F
determined by the product of resistor R
OFF
(1)Oscillator operation when intermittent action
and OSC control circuit does not operate
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
from the constant voltage source
ON
of 5.8V.C
is charged up by the same amplitude as R
F
current,when internal switch SW1 is switched to "charging
side".The rise rate of C
terminal is given as
F
V
-
~
T
ON
(V/s) ................................................(1)
R
X C
ON
F
~
where V
-
4.5V
T
ON
The maximum on duration is approximately given as
(V
-V
) X R
X C
~
OSCH
OSCL
ON
F
(s) ........................(2)
V
-
T
ON
~
where V
4.4V
OSCH
~
2.0V
V
OSCL
C
is discharged by the summed-up of R
F
sixteenth (1/16) of R
when SW1,SW2 are switched to "discharge side".
.
R
ON
makes start-up
to
(START)
R
OFF
C
F
Fig.4 Schematic diagram of charging and discharging
V
OSCH
~
4.4V
V
OSCL
~
2.0V
V
OH
and capacitor C
.
F
V
OL
Fig.5 OSC.waveform at normal condition (no-
So fall rate of CF terminal is given as
ON
~
V
-
T
OFF
R
X C
OFF
The minimum off duration approximately is given as
~
(V
OSCH
V
-
T
OFF
R
OFF
where V
-
T
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.
(
13
/ 27 )
MITSUBISHI (Dig./Ana. INTERFACE)
M51995AP/FP
SWITCHING REGULATOR CONTROL
current and one
OFF
current by the function of Q2,Q3 and Q4
ON
Q4
Q1
1/16
T-ON
Q3
T-OFF
FROM
VF SIGNAL
~
Vz 4.2V
CF
Q2
M51995
control circuit for OSC.capacitor C
operation of intermittent action and OSC.control
circuit)
V
-
T
ON
+
(V/s)
.....................(3)
16 X R
X C
F
ON
F
-V
) X C
OSCL
F
(s) .....................................(4)
V
-
T
ON
+
16 X R
ON
~
3.5V
OFF
5.8V
CHARGING
SW1
SWITCHED BY
CHARGING AND
DISCHARGING
SIGNAL
SW2
DISCHARGING
F