SC5010H View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
SC5010H
Semtech Corporation
'SC5010H' PDF : 36 Pages View PDF
SC5010H
PCB Layout Considerations
The placements of the power components outside the
SC5010H should follow the layout guidelines of a general
boost converter. The Detailed Application Circuit is used
as an example.
1. Capacitor (C2) should be placed as close as possible to
the VCC and AGND to achieve the best performance.
2. Capacitor (C1) is the input power filtering capacitor
for the boost, it needs to be tied to PGND.
3. The converter power train inductor (L1) is the boost
converter input inductor. Use wide and short traces
connecting these components.
4. The output rectifying diode (D1) uses a Schottky
diode for fast reverse recovery. Transistor (Q1) is the
external switch. Resistor (R9) is the switch current
sensing resistor. To minimize switching noise for the
boost converter, the output capacitor (C6) should be
placed such that the loop formed by Q1, D1, C6 and
R9, is minimized. The output of the boost converter is
used to power up the LEDs. Use wide and short trace
connecting Pin DRVN and the gate of Q1. The GNDs
for R9 and C6 should be PGND. These components
should be close to the SC5010H.
5. Resistor (R8) is the output current adjusting resistor
for IO1 through IO8 and should return to AGND. Place
it next to the IC.
6. Resistor (R6) is the switching frequency adjusting
resistor and should return to AGND. Place it next to
the IC.
7. The decoupling capacitor (C3) for Pin BG should return
to AGND. Place it next to the IC.
8. Resistors (R4, R5) form a divider to set the SCP level, R4
should return to AGND. Place it next to the IC.
9. Resistors (R2, R1) form a divider to set the UVLO level
for VIN. R1 should return to AGND. Place it next to the
IC.
10. R11 and R10 form a divider to set the OVP level for
VOUT, R10 should return to AGND. Place it next to the
IC.
11. All the traces for components with AGND connection
should avoid being routed close to the noisy areas.
12. An exposed pad is located at the bottom of the
SC5010H for heat dissipation. A copper area
underneath the pad is used for better heat dissipation.
On the bottom layer of the PCB another copper area,
connected through vias to the top layer, is used for
better thermal performance. The pad at the bottom
of the SC5010H should be connected to AGND. AGND
should be connected to PGND at single point for
better noise immunity.
Components Selection
Inductor Selection
The choice of the inductor affects the converter’s steady
state operation, transient response, and its loop stability.
Special attention needs to be paid to three specifications
of the inductor, its value, its DC resistance and saturation
current. The inductor’s inductance value also determines
the inductor ripple current. The boost converter will
operate in either CCM (Continuous Conduction Mode) or
DCM (Discontinuous Conduction Mode) depending on its
operating conditions. The inductor DC current or input
current can be calculated using the following equation.
,,1
9287 u ,287
9,1 u Ș
IIN — Input current; IOUT — Output current;
VOUT — Boost output voltage;
VIN — Input voltage;
η — Efficiency of the boost converter.
Then the duty ratio under CCM is shown by the following
equation.
D VOUT VIN VD
VOUT VD
VD – Forward conduction drop of output rectifying diode
When the boost converter runs under DCM ( L < Lboundary),
it takes the advantages of small inductance and quick
transient response; where as if the boost converter works
under CCM (L > Lboundary), normally the converter has higher
efficiency.
When selecting an inductor, another factor to consider is
the peak-to-peak inductor current ripple, which is given
by the following equation.
24
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