MCP16323T-ADJE Datasheet, PDF (20/32 Pages) Microchip Technology – 18V Input, 3A Output, High Efficiency Synchronous Buck Regulator with Power Good Indication

MCP16323
TABLE 5-1: CAPACITOR VALUE RANGE
Parameter
Min
Max
C_OUT
33 µF
None
5.0.6 INDUCTOR SELECTION
The MCP16323 is designed to be used with small
surface mount inductors. Several specifications should
be considered prior to selecting an inductor. To
optimize system performance, low ESR inductors
should be used.
EQUATION 5-3: INDUCTOR CURRENT
RIPPLE
ΔI_L=
V----_L-
L
×
t_ON
EXAMPLE 5-3:
MCP16323 PEAK
INDUCTOR CURRENT – 3A
V_IN = 12V
V_OUT = 3.3V
I_OUT = 3A
L = 4.7 µH
ILPK
=
Δ_-----I--L--
2
+
IOUT
Inductor ripple current = 509 mA
Inductor peak current = 3.255A
An inductor saturation rating minimum of 3.255A is
recommended. A trade-off between size, cost and
efficiency is made to achieve the desired results.
TABLE 5-2: MCP16323 RECOMMENDED
INDUCTORS
Part Number
Value
(µH)
Coilcraft^®
MSS6132-472 4.7
LPS6225-472 4.7
MSS7341-502 4.7
DO1813H-472 4.7
Wurth Elektronik^®
7447785004 4.7
7447786004 4.7
7447789004 4.7
EPCOS^®
B82464G2
4.7
B82464A2
4.7
DCR
(Ω)
0.056
0.065
0.024
0.054
0.06
0.057
0.033
0.033
0.03
I_SAT
(A)
Size
WxLxH
(mm)
2.84 6.1x6.1x3.2
3.2 6.2x6.2x2.5
3.16 7.3x7.3x4.1
2.6 8.89x6.1x5.0
2.5 5.9x6.2x3.3
2.8 5.9x6.2x5.1
3.9 7.3x3.2x1.5
3.1 10.4x10.4x3.0
4.5 10.4x10.4x3.0
DS22284A-page 20
5.0.7 BOOST CAPACITOR
The boost capacitor is used to supply current for the
internal high-side drive circuitry that is above the input
voltage. The boost capacitor must store enough energy
to completely drive the high-side switch on and off. A
22 nF X5R or X7R capacitor is recommended for all
applications. The boost capacitor maximum voltage is
5.5V, so a 6.3V or 10V rated capacitor is
recommended.
5.0.8 THERMAL CALCULATIONS
The MCP16323 is available in a 3x3 QFN-16 package.
By calculating the power dissipation and applying the
package thermal resistance (θ_JA), the junction
temperature is estimated. The maximum continuous
junction temperature rating for the MCP16323 is
+125°C.
To quickly estimate the internal power dissipation for
the switching step-down regulator, an empirical
calculation using measured efficiency can be used.
Given the measured efficiency, the internal power
dissipation is estimated in Equation 5-4. This power
dissipation includes all internal and external
component losses. For a quick internal estimate,
subtract the estimated inductor ESR loss from the P_DIS
calculation in Equation 5-4.
EQUATION 5-4: TOTAL POWER
DISSIPATION ESTIMATE
P_DIS
=
V----_{O----U---T----}×_{-----I--O----U---T-}
Efficency
–
(
V_OUT
×
I_OU
T
)
The difference between the first term, input power, and
the second term, power delivered, is the total system
power dissipation. The inductor losses are estimated
by P_L = I_OUT2 x L_ESR.
EXAMPLE 5-4: POWER DISSIPATION
V_IN = 12V
V_OUT = 5.0V
I_OUT = 3 A
Efficiency = 88%
Total System Dissipation = 2.05 W
L_ESR = 0.02 Ω
P_L = 180 mW
MCP16323 internal power dissipation estimate:
P_DIS – P_L = 1.87 W
θ_JA = 38.5°C/W
Estimated Junction = +71.995°C
Note 1:
2:
θ_JA =
Board
38.5°C/W for a
with a 13.5 in²,
4-layer FR4
1 oz internal
Printed
copper
Circuit
ground
plane.
A smaller ground plane will result in a larger θ_JA
temperature rise.
© 2011 Microchip Technology Inc.