AS1341
Datasheet - Application Information
Maximum Output Current
The AS1341 output current determines the regulator’s switching frequency. When the converter approaches continu-
ous mode, the output voltage falls out of regulation. For the typical application, the maximum output current is approxi-
mately:
ILOADMAX = 1/2 x ILXPEAKMIN
For low-input voltages, the maximum on-time may be reached and the load current is limited by:
ILOAD = (1/2 x (VIN - VOUT) x 10µs)/L
(EQ 5)
(EQ 6)
Output Capacitor
Choose the output capacitor to service the maximum load current with acceptable voltage ripple. The output ripple has
two components: variations in the charge stored in the output capacitor with each LX pulse, and the voltage drop
across the capacitor’s equivalent series resistance (ESR) caused by the current into and out of the capacitor:
VRIPPLE ≅ VRIPPLEESR + VRIPPLEC
The output voltage ripple as a consequence of the ESR and output capacitance is:
VRIPPLEESR = ESR x IPEAK
(EQ 7)
(EQ 8)
(EQ 9)
VRIPPLEC = (L x (IPEAK - IOUTPUT)2)/(2 x (COUT x VOUTPUT)) x VIN/(VIN - VOUTPUT)
Where:
IPEAK is the peak inductor current (see Inductor Selection on page 11). The worst-case ripple occurs at no-load.
Equations EQ 7, EQ 8, and EQ 9 are suitable for initial capacitor selection, but actual values should be set by testing a
prototype or evaluation circuit. As a general rule, a smaller amount of charge delivered in each pulse results in less
output ripple. Since the amount of charge delivered in each oscillator pulse is determined by the inductor value and
input voltage, the voltage ripple increases with larger inductance, and as the input voltage decreases.
Table 6. Recommended Output Capacitor
Part Number
T520V107M010ATE018
A700V826M006ATE018
T520B107M006ATE040
T520A336M006ATE070
A700V226M006ATE028
510X107M020ATE040
EEFUD0J101R
C
ESR
Rated Voltage
10V
Manufacturer
Kemet
www.kemet.com
100µF
82µF
100µF
33µF
22µF
10µF
100µF
33µF
100µF
47µF
18mΩ
18mΩ
40mΩ
70mΩ
28mΩ
40mΩ
15mΩ
18mΩ
55mΩ
70mΩ
6.3V
6V
6.3V
6.3V
20V
Panasonic
www.panasonic.com
6.3V
8V
EEFCD0K330R
Sanyo
www.edc.sanyo.com
10TPB100ML
10V
6TPB47M
6.3V
www.austriamicrosystems.com
Revision 1.05
12 - 17
AMSCO [ AMS(艾迈斯) ]
