m51996ap Renesas Electronics Corporation., m51996ap Datasheet - Page 14

• Manufacturer Part Number: m51996ap
• Description: Switching Regulator Control
• Manufacturer: Renesas Electronics Corporation.

M51996AP/AFP
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
mainly determined by the product of resistor R
1. Oscillator operation when SOFT circuit does not operate
REJ03D0836-0201 Rev.2.01 Nov 14, 2007
Page 14 of 35
Figure 3 shows the equivalent charging and discharging circuit diagram of oscillator.
The current flows through R
as R
as
The maximum on duration is approximately given as
C
Q3 and Q4 when SW1, SW2 are switched to “discharge side”.
So fall rate of CF terminal is given as
The minimum off duration approximately is given as
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.
F
is discharged by the summed-up of R
≈
where V
≈
where V
≈
≈
ON
current, when internal switch SW1, SW2 is switched to “charging side”. The rise rate of C
R
R
(V
ON
V
OFF
V
(V
V
T-ON
OSCH
T-OFF
R
V
T-OFF
× C
OSCH
OFF
T-ON
OSCH
OSCL
× C
F
Waveform of CF terminal
− V
F
− V
(V/s) ………………………………………… (1)
OSCL
4.5 V
V
+
+
2.0 V
4.4 V
(no-operation of intermittent action and OSC control circuit)
OSCL
T-ON
16 × R
16 × R
Waveform of V
terminal in Max
ON duty condition
) × R
V
) × C
T-ON
V
ON
Figure 2 OSC. Waveform at Normal Condition
T-ON
ON
ON
ON
F
from the constant voltage source of 5.8 V. C
× C
× C
F
F
(s) …………………… (4)
OUT
(V/s) ………………… (3)
OFF
(s) ………………… (2)
≈ 4.4 V
≈ 2.0 V
OFF
V
V
current and one sixteenth (1/16) of R
OSCH
OSCL
V
V
OH
and capacitor C
OL
F
.
ON
and capacitor C
F
is charged up by the same amplitude
ON
current by the function of Q2,
F
and the falling duration is
F
terminal is given