MIC5191 MICREL [Micrel Semiconductor], MIC5191 Datasheet - Page 11

• Manufacturer Part Number: MIC5191
• Description: Ultra High-Speed, High-Current Active Filter / LDO Controller
• Manufacturer: MICREL [Micrel Semiconductor]

Referring to Application Hint 17, Designing PCB Heat
Sinks , the minimum amount of copper area for a D
at 28.8°C/W is 2750mm
denotes convection heating only (2 oz. copper) and the
dotted line shows thermal resistance with 250LFM air-
flow. The copper area can be significantly reduced by
increasing airflow or by adding external heat sinks.
Another important characteristic is the amount of gate
capacitance. Large gate capacitance can reduce
transient performance by reducing the ability of the
MIC5190 to slew the gate. It is recommended that the
MOSFET used has an input capacitance <10nF (C
Source threshold specified in most MOSFET data sheets
refers to the minimum voltage needed to fully enhance
the MOSFET. Although for the most part, the MOSFET
will be operating in the linear region and the V
Micrel, Inc.
December 2006
CSH
+V
12V
V
V
EN
J1
J2
OUT
OUT
IN
Figure 8. PC Board Heat Sink
100k
10k
11.5k
V
100pF
IN
1µF
25V
560pF
2
8.06k
330µF
6
2
4
5
3
1
(or 0.426in
16V
VIN
EN/UVLO
CSH
VOUT
FB
COMP
U1 MIC2198-BML
10µF
GND
9
VSW
HSD
VDD
10µF
BST
LSD
2
12
11
10
8
7
). The solid line
10µF
0.1µF
2.2µF
10V
D1
SD103BWS
IRF7821
IRF7821
GS
Figure 9. Post Regulator
ISS
(gate-
2
CDEP134-1R8MC-H
pack
).
D2
1N5819HW
1.8µH
L1
11
CSH
Tantalum
source voltage) will be less than the fully enhanced V
it is recommended the VCC voltage has 2V over the
minimum V
saturation voltage of the MIC5191 output driver.
For our example, with a 1.5V output voltage, our
MOSFET is fully enhanced at 4.5V
should be greater or equal to 8V.
Input Capacitor
Good input bypassing is important for improved perfor-
mance. Low ESR and low ESL input capacitors reduce
both the drain of the N-Channel MOSFET, as well as the
source impedance to the MIC5191. When a load
transient on the output occurs, the load step will also
appear on the input. Deviations on the input voltage will
be reduced by the MIC5191’s PSRR, but nonetheless
appear on the output. There is no minimum input
capacitance,
recommended that the input capacitance be equal to or
greater than the output capacitance.
Output Capacitor
The MIC5191 is stable with any type or value of output
capacitor (even without any output capacitor!). This
allows the output capacitor to select which parameters of
the regulator are important. In cases where transient
response is the most important, low ESR and low ESL
ceramic capacitors are recommended. Also, the more
capacitance on the output, the better the transient
response.
10k
330µF
V
OUT
V
OUT
V
CC1, 2
GS
≥ 2V + V
and output voltage. This is due to the
but
OUT
VIN
ISENSE
GND
MIC5191
for
COMP
GS
VCC1
VCC2
FB
+ V
optimal
10µF
OUT
12.4k
10nF
22µF
10µF
performance
GS
, our V
1V
OUT
M9999-122206
@10A
1µF
CC
MIC5191
voltage
it
GS
is
,