MIC2199 MICREL [Micrel Semiconductor], MIC2199 Datasheet - Page 14

• Manufacturer Part Number: MIC2199
• Manufacturer: MICREL [Micrel Semiconductor]

MIC2199
Decoupling Capacitor Selection
The 4.7µF decoupling capacitor is used to minimize noise on
the V
proper operation of the IC. It must be placed right next to the
pins and routed with a wide trace. The capacitor should be a
good quality tantalum. An additional 1µF ceramic capacitor
may be necessary when driving large MOSFETs with high
gate capacitance. Incorrect placement of the V
capacitor will cause jitter or oscillations in the switching
waveform and large variations in the overcurrent limit.
A 0.1µF ceramic capacitor is required to decouple the V
The capacitor should be placed near the IC and connected
directly to between pin 6 (V
PCB Layout and Checklist
PCB layout is critical to achieve reliable, stable and efficient
performance. A ground plane is required to control EMI and
minimize the inductance in power, signal and return paths.
The following guidelines should be followed to insure proper
operation of the circuit.
MIC2199
• Signal and power grounds should be kept separate
• The connection between the current-sense resis-
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and connected at only one location. Large currents
or high di/dt signals that occur when the MOSFETs
turn on and off must be kept away from the small
signal connections.
tor and the MIC2199 current-sense inputs (pin 4
and 5) should have separate traces, through a 10Ω
resistor on each pin. The traces should be routed
as closely as possible to each other and their
length should be minimized. Avoid running the
traces under the inductor and other switching
components. The 10Ω resistor should be placed
close as possible to pins 4 and 5 on the MIC2199
and a 1nF to 0.1µF capacitor placed between pins
4 and 5 will help attenuate switching noise on the
current sense traces. This capacitor should be
placed close to pins 4 and 5.
pin. The placement of this capacitor is critical to the
IN
) and pin 9 (GND).
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decoupling
IN
.
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• When the high-side MOSFET is switched on, the
• When the low-side MOSFET is switched on, cur-
• The freewheeling diode, D1 in Figure 2, conducts
• The 4.7µF capacitor, which connects to the V
• The V
critical flow of current is from the input capacitor
through the MOSFET, inductor, sense resistor,
output capacitor, and back to the input capacitor.
These paths must be made with short, wide pieces
of trace. It is good practice to locate the ground
terminals of the input and output capacitors close
to each.
rent flows through the inductor, sense resistor,
output capacitor, and MOSFET. The source of the
low-side MOSFET should be located close to the
output capacitor.
current during the dead time, when both MOSFETs
are off. The anode of the diode should be located
close to the output capacitor ground terminal and
the cathode should be located close to the input
side of the inductor.
terminal (pin 7) must be located right at the IC. The
V
of this capacitor is very critical. Connections must
be made with wide trace. The capacitor may be
located on the bottom layer of the board and
connected to the IC with multiple vias.
to the IC and connected between pins 6 and 9.
Connections should be made with a ground and
power plane or with short, wide trace.
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terminal is very noise sensitive and placement
IN
bypass capacitor should be located close
November 2004
DD
Micrel