AMS34063
APPLICATION HINTS
Design Formula Table
Calculation
tON
tOFF
(tON + tOFF) MAX
CT
IPK(switch)
Step-Down
VOUT + VF
VIN(MIN) - VSAT - VOUT
1
fMIN
4 x 10-5tON
2IOUT(MAX)
RSC
L(MIN)
CO
0.33/IPK(switch)
VIN(MIN) − VSAT
IPK(switch)
−
VOUT
tON(MAX)
IPK(switch) (tON + tOFF)
8Vripple(P − P)
VSAT = Saturation voltage of the output switch.
VF = Forward voltage drop of the ringback rectifier.
Step-Up
VOUT + VF - VIN(MIN)
VIN(MIN) - VSAT
1
fMIN
4 x 10-5tON
2IOUT(MAX) tON + tOFF
tOFF
0.33/IPK(switch)
VIN(MIN) − VSAT
IPK(switch)
tON(MAX
)
≈ IOUT tON
Vripple
Notes
The following power supply characteristics must be chosen:
VIN – Nominal input voltage. If this voltage is not constant, then use VIN(MAX) for step-down and VIN(MIN) for step-up converter.
VOUT – Desired output voltage,
VOUT =1.25 1 +
R2 .
R1
IOUT - Desired output current.
fMIN - Minimum desired output switching frequency at the selected values for VIN and IO.
Vripple(P-P) – Desired peak-to-peak output ripple voltage. In practice, the calculated value will need to be increased due to the
capacitor’s equivalent series resistance and board layout. The ripple voltage should be kept to a low value since it will
directly effect the line and load regulation.
Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140