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IR3863MPBF
1.5 V ? ? 1 6 V - 1.5 V ?
1 6 V ? 3 . 3 ? H ? 300k Hz
DESIGN EXAMPLE
Design Criteria:
Input Voltage, VIN, = 7V to 16V
Output Voltage, VOUT = 1.5V
Switching Frequency, Fs = 300kHz
Inductor Ripple Current, 2ΔI = 1.5A
Maximum Output Current, IOUT = 6A
However, if space allows, PIMB104T-3R3MS-
39 (11mm x 10mm) with 10.8 mΩ DCR will
provide higher efficiency. Ripple current needs
to be recalculated using the chosen inductor.
2 Δ I ? ? 1 . 37 A
Choose an input capacitor:
1 ? 1 . 37 A / 2 ?
Over Current Trip, IOC = 9A
Overshoot Allowance for 3A Load Step Down,
VOS = VOUT + 50mV
I IN_RMS ? 6 A ?
1.5V
1 6 V
? 1 ? ? ? ? ? 1 . 8 A
3 ? 6 A ?
2
Undershoot Allowance for 3A Load Step Up,
VDROP = 50mV
A
Panasonic
10μF
(ECJ3YB1E106M)
Find R FF :
R FF ?
1.5 V
1 V ? 20 pF ? 300k Hz
? 2 50 k ?
accommodates 6 Arms of ripple current at
300kHz. Due to the chemistry of multilayer
ceramic capacitors, the capacitance varies over
temperature and operating voltage, both AC and
Pick a standard value 255 kΩ, 1% resistor.
DC. One 10μF capacitor is recommended. In a
practical solution, one 1μF capacitor is required
Find R SET :
R SET ?
20.1m ? ? 9 A
1 9 ? A
? 9 . 5 k ?
along with 10μF. The purpose of the 1μF
capacitor is to suppress the switching noise and
deliver high frequency current.
Pick a 9.53 kΩ, 1% standard resistor.
Find a resistive voltage divider for V OUT = 1.5V:
Choose an output capacitor:
To meet the undershoot and overshoot
specification, equation 7b and 8 will be used to
V FB ?
R 2
R 2 ? R 1
? V OUT ? 0.5 V
calculate the minimum output capacitance. As a
result, 130μF will be needed for 3A load
removal. To meet the stability requirement,
V OUT ? ? V IN ? V OUT ?
1.5 V ? ? 1 6 V - 1.5 V ?
R 2 = 1.40k Ω , R 1 = 2.80 kΩ, both 1% standard
resistors .
Choose the soft start capacitor:
Once the soft start time has chosen, such as
1000us to reach to the reference voltage, a
22nF for C SS is used to meet 1000μs.
Choose an inductor to meet the design
specification:
L ?
V IN ? 2 ΔI ? F s
?
1 6 V ? 1 . 5 A ? 300k Hz
choose an output capacitors with ESR larger
than 16 mΩ . Combine those two requirements,
one can choose a set of output capacitors from
manufactures such as SP-Cap (Specialty
Polymer Capacitor) from Panasonic or POSCAP
from Sanyo. A 150μF (4TPE150M) from Sanyo
with 25 mΩ ESR will meet both requirements.
If an all ceramic output capacitor solution is
desired, the external slope injection circuit
composed of R6, C13, and C14 is required as
explained in the Stability Consideration Section.
In this design example, we can choose C14 =
1nF and C13 = 100nF. To calculate the value of
R6 with PCMB065T-3R3MS as our inductor:
? 3.0 ? H
Choose an inductor with low DCR and AC
R 6 ?
L
DCR ? C 13
3 . 3 ? H
power loss to increase the overall system
efficiency based on allowed physical size
requirement. For instance, PCMB065T-3R3MS
from CYNTEC is a 7mm x 6.6mm inductor with
19.9 mΩ DCR.
8/8/2012 Rev3.2
?
19 . 9 m ? ? 100 nF
? 1 . 66 k ?
Pick a standard value for R6 = 1.65 kΩ .
16
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