M5291P/FP
Constant Definition
Constant
TON
TOFF
(TON + TOFF) MAX
TOFF
TON
Step-down Circuit
VOUT + VF
VIN (MIN) − Vsat −VOUT
1
fMIN
TON + TOFF
1+
TON
TOFF
1
fMIN
− TOFF
Step-up Circuit
VOUT + VF − VIN (MIN)
VIN (MIN) − Vsat
1
fMIN
TON + TOFF
1+
TON
TOFF
1
fMIN
− TOFF
Inverse Polarity Circuit
VOUT + VF
VIN − Vsat
1
fMIN
TON + TOFF
1+
TON
TOFF
1
fMIN
− TOFF
CT
IPK
L (MIN)
RSC
VO
6 × 10−5 • TON
2 • IOUT (MAX)
(
VIN
(MIN)
− Vsat
IPK
−
VOUT
)
• TON (MAX)
0.33
IPK
1.17 × (1 +
R1
R2
)
6 × 10−5 • TON
2 • IOUT (MAX) • ( 1 +
TON
TOFF
)
(
VIN (MIN) − Vsat
IPK
)
• TON (MAX)
0.33
IPK
1.17 × (1 +
R1
R2
)
6 × 10−5 • TON
2 • IOUT (MAX) •
(1 +
TON
TOFF
)
(
VIN (MIN) − Vsat
IPK
)
• TON (MAX)
0.33
IPK
1.17 × (1 +
R1
R2
)
Note: VF: Forward Voltage of Diode
Vsat: Output saturation voltage of M5291 (0.6 Vmax at single output, 2.0 Vmax at Darlington output)
Setting switching frequency first and calculate each constant value.
Notes:
1. Peak current sense
In overcurrent function, oscillator is stop, when voltage descend of external detecting resistance is more than 330
mV.
2. ON/OFF Control
If you need stop the action, connected resistance (5 to 10 kΩ) between supply voltage terminal and timing capacitor
terminal.
3.
TON
TON + TOFF
is not established more than 0.857, because charge and discharge current ratio fixed 1 : 6.
REJ03D0841-0300 Rev.3.00 Jun 15, 2007
Page 7 of 9