ML4863 Просмотр технического описания (PDF) - Micro Linear Corporation
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ML4863 Datasheet PDF : 10 Pages
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ML4863
DESIGN CONSIDERATIONS (Continued)
3c. Specify the inductor’s DC winding resistance:
LDCR = 90mW
3d. Specify the coupled inductor's turn ratio:
Np : Ns = 1:1
4a. Calculate the minimum output capacitance
required using equation 5.
C = 0.50 ×
5+6
5
× 2.5 × 10−6
0.1
= 55µF
(5a)
4b. Establish the maximum ESR for the output
capacitor using equation 6.
RESR
<
0.1× 0.12
150mV
= 80mW
(6a)
Based on these calculations, the design should use two
100µF capacitors, with an ESR of 100mW each, in parallel
to meet the capacitance and ESR requirements.
5.
As a final design check, evaluate the system
stability using equation 7.
! "$# 100mV ≤ (6 × 10−6) ×
0.12 × (5 + 4)
18 × 10–6
= 360mV (7a)
Since the inequality is met, the circuit should be stable.
Some typical application circuits are shown in Figures 2, 3,
and 4.
LAYOUT
Good PC board layout practices will ensure the proper
operation of the ML4863. Important layout considerations
follow:
• The connection from the current sense resistor to the
SENSE pin of the ML4863 should be made by a
separate trace and connected right at the sense resistor
lead.
• The VCC bypass capacitor needs to be located close to
the ML4863 for adequate filtering of the IC's internal
bias voltage.
• Trace lengths from the capacitors to the inductor, and
from the inductor to the FET should be as short as
possible to minimize noise and ground bounce.
• Power and ground planes must be large enough to
handle the current the converter has been designed for.
See Figure 5 for a sample PC board layout.
VIN
47µF
8
Coiltronics
CTX20-4
VOUT
5V, 1A
400µF
ML4863
VIN
GND
SENSE OUT 2
SHDN OUT 1
VFB
VCC
1µF
NDS9955
VIN
100µF
100mΩ
Figure 2. 5V, 1A Circuit
Dale
LPE6562
VOUT
5V, 2A
800µF
ML4863
VIN
GND
SENSE OUT 2
SHDN OUT 1
VFB
VCC
1µF
NDS9410
NDS9410
50mΩ
Figure 3. 5V, 2A Circuit
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