Datasheet

© 2011 Microchip Technology Inc. DS25004A-page 19
MCP16301
5.7 Freewheeling Diode
The freewheeling diode creates a path for inductor cur-
rent flow after the internal switch is turned off. The aver-
age diode current is dependent upon output load
current at duty cycle (D). The efficiency of the converter
is a function of the forward drop and speed of the free-
wheeling diode. A low forward drop Schottky diode is
recommended. The current rating and voltage rating of
the diode is application dependent. The diode voltage
rating should be a minimum of V
IN
, plus margin. For
example, a diode rating of 40V should be used for an
application with a maximum input of 30V. The average
diode current can be calculated using
Equation 5-6.
EQUATION 5-6: DIODE AVERAGE
CURRENT
EXAMPLE 5-4:
A 0.5A to 1A diode is recommended.
5.8 Boost Diode
The boost diode is used to provide a charging path from
the low voltage gate drive source, while the switch
node is low. The boost diode blocks the high voltage of
the switch node from feeding back into the output volt
-
age when the switch is turned on, forcing the switch
node high.
A standard 1N4148 ultra-fast diode is recommended
for its recovery speed, high voltage blocking capability,
availability and cost. The voltage rating required for the
boost diode is V
IN
.
For low boost voltage applications, a small Schottky
diode with the appropriately rated voltage can be used
to lower the forward drop, increasing the boost supply
for gate drive.
TABLE 5-3: MCP16301 RECOMMENDED
3.3V INDUCTORS
Part Number
Value
(µH)
DCR (Ω)
I
SAT
(A)
Size
WxLxH
(mm)
Coilcraft
®
ME3220 15 0.52 0.90 3.2x2.521.0
LPS4414 15 0.440 0.92 4.3x4.3x1.4
LPS6235 15 0.125 2.00 6.0x6.0x3.5
MSS6132 15 0.135 1.56 6.1x6.1x3.2
MSS7341 15 0.057 1.78 7.3x7.3x4.1
ME3220 15 0.520 0.8 2.8x3.2x2.0
XFL2006 15 2.02 0.25 2.0x2.0x0.6
LPS3015 15 0.700 0.61 3.0x3.0x1.4
Wurth Elektronik
®
744028 15 0.750 0.35 2.8x2.8x1.1
744029 15 0.600 0.42 2.8x2.8x1.35
744025 15 0.400 0.900 2.8x2.8x2.8
744031 15 0.255 0.450 3.8x3.8x1.65
744042 15 0.175 0.75 4.8x4.8x1.8
Coiltronics
®
SD12 15 0.48 0.692 5.2x5.2x1.2
SD18 15 0.266 0.831 5.2x5.2x1.8
SD20 15 0.193 0.718 5.2x5.2x2.0
SD3118 15 0.51 0.75 3.2x3.2x1.8
SD52 15 0.189 0.88 5.2x5.5.2.0
Sumida
®
CDPH4D19F 15 0.075 0.66 5.2x5.2x2.0
CDRH2D09C 15 0.52 0.24 3.2x3.2x1.0
CDRH2D162D 15 0.198 0.35 3.2x3.2x1.8
CDRH3D161H 15 0.328 0.65 4.0x4.0x1.8
TDK - EPC
®
VLF3012A 15 0.54 0.41 2.8x2.6x1.2
VLF30251 15 0.5 0.47 2.5x3.0x1.2
VLF4012A 15 0.46 0.63 3.5x3.7x1.2
VLF5014A 15 0.28 0.97 4.5x4.7x1.4
B82462G4332M 15 0.097 1.05 6x6x2.2
TABLE 5-4: FREEWHEELING DIODES
App Manufacturer
Part
Number
Rating
12 V
IN
600 mA
Diodes
Inc.
DFLS120L-7 20V, 1A
24 V
IN
100 mA
Diodes
Inc.
B0540Ws-7 40V, 0.5A
18 V
IN
600 mA
Diodes
Inc.
B130L-13-F 30V, 1A
I
D1AVG
1D–()I
OUT
× =
I
OUT
=0.5A
V
IN
=15V
V
OUT
=5V
D=5/15
I
D1AVG
=333 mA