AS1310
Datasheet - Detailed Description
Figure 13. Simplified Voltage and Current Waveforms
V
0.99VOUT_NOM
VOUT
VOUT Ripple
VIND_TOFF
B
C
B
C
VIN
0
VIND_TON
D
A
D
T
TOFF TWAIT
TON
TOFF TWAIT
IL
SW1_on
SW2_off
IPK
0
T
SW2_on
SW1_off
T
T
Another important relationship is the “volt-seconds” law. Expressed as following:
VONTON = VOFFTOFF
(EQ 4)
Voltages are those measured across the inductor during each time segment. Figure 13 shows this graphically with the shaded segments marked
“A & B”. Re-arranging (EQ 4):
T
V
OUT – VIN
------O---N---
TOFF
----------------------------
=
(EQ 5)
VIN
The time segment called TWAIT in Figure 13 is a measure of the “hold-up” time of the output capacitor. While the output voltage is above the
threshold (0.99xVOUT), the output is assumed to be in regulation and no further switching occurs.
8.1.2 Inductor Choice Example
For the AS1310 VIN_MIN = 0.9V, VOUT_MAX = 3.3V, (EQ 5) gives Ton=2.66TOFF
.
Let the maximum operating on-time = 1µs.
Note that this is shorter than the minimum limit on-time of 3.6µs. Therefore from (EQ 5), TOFF = 0.376µs. Using (EQ 3), LMAX is obtained:
LMAX = 1.875µH. The nearest preferred value is 2.2µH.
This value provides the maximum energy storage for the chosen fixed on-time limit at the minimum VIN.
www.austriamicrosystems.com/DC-DC_Step-Up/AS1310
Revision 1.8
9 - 19
AMSCO [ AMS(艾迈斯) ]
