M62216FP/GP
Equation for Constants Calculation
Constants
TON
TOFF
TON + TOFF
TOFF (MIN)
TON (MAX)
lpk
L (MIN)
R1
RD1
RD2
Standard Application Circuit
VO + VF − VIN
VIN − VCE (sat)
1
fOSC
TON + TOFF
1 + TON
TOFF
1
fOSC
− TOFF (MIN)
2×
1 + TON
TOFF
× (lO + lB)
(VIN − VCE (sat))2 × TON (MAX)2 × fOSC
2 × VO × (lO + lB)
VO − 1 × R2
VREF
VO − (VBE + Vsat1)
(lpk/hFE) × A1
VO − (VBE + Vsat2)
(lpk/hFE) × A2
Application Circuit 1
VO + VF − VIN
VIN − VCE (sat)
1
fOSC
TON + TOFF
1 + TON
TOFF
1
fOSC
− TOFF (MIN)
2×
1 + TON
TOFF
× lO
(VIN − VCE (sat))2 × TON (MAX)2 × fOSC
2 × VO × lO
VO − 1 × R2
VREF
VO− (VBE + Vsat1)
(lpk/hFE) × A1
VO − (VBE + Vsat2)
(lpk/hFE) × A2
Application Circuit 2
VO + VF − VIN
VIN − VCE (sat)
1
fOSC
TON + TOFF
1 + TON
TOFF
1
fOSC
− TOFF (MIN)
2×
1 + TON
TOFF
× lO
(VIN − VCE (sat))2 × TON (MAX)2 × fOSC
2 × VO × lO
VO − 1 × R2
VREF
VIN − (VBE + Vsat1)
(lpk/hFE) × A1
VIN − (VBE + Vsat2)
(lpk/hFE) × A2
Constants
TON
TOFF
TON + TOFF
TOFF (MIN)
TON (MAX)
lpk
L (MIN)
R1
RD1
RD2
STEP-DOWN Circuit
VO + VF
VIN − VCE (sat) − VO
1
fOSC
TON + TOFF
1 + TON
TOFF
1
fOSC
− TOFF (MIN)
2 × lO
(VIN − VCE (sat) − VO) × TON (MAX)
∆lO
VO − 1 × R2
VREF
VO − VBE − Vsat1
lpk/hFE
VIN − Vsat2
(lpk/hFE) × A3
Note:
VF: Forward voltage of external diode.
VCE (sat): Saturation voltage of external transistor.
VBE: Voltage between Base - Emitter of external transistor.
hFE: hFE of external transistor at saturating.
A1: Ratio of current into DRIVE1 terminal.
(A1 = 0.8~0.9)
A2: Ratio of current into DRIVE2 terminal.
(A2 = 1 − A1)
A3: Ratio of current into DRIVE2 terminal.
(A3 = 0.1~0.2)
• Set R2 to several kΩ ~ several 10ths kΩ.
• Set current into DRIVE2 terminal more than 100 µA.
(Ipk / hFE) × A2 ≥ 100 µA, (Ipk / hFE) × A3 ≥ 100 µA
• Set ∆IO to 1/5 ~ 1/3 of maximum load current
• The maximum rating of current of external parts (transistor,
diode and inductor) are 1.5 to 2 times of Ipk.
REJ03D0845-0300 Rev.3.00 Jun 15, 2007
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