MIC5190
Micrel
The gate-source threshold specified in most MOSFET data
sheetsreferstotheminimumvoltageneededtofullyenhance
theMOSFET. Althoughforthemostpart, theMOSFET willbe
Deviations on the input voltage will be reduced by the
MIC5190’s PSRR, but nonetheless appear on the output.
There really is no minimum input capacitance, but it is
recommended that the input capacitance be equal to or
greater than the output capacitance for best performance.
operating in the linear region and the V
(gate-source
GS
voltage) will be less than the fully enhanced V , it is
GS
recommended the V
voltage has 2V over the minimum
Output Capacitor
CC
V
and output voltage. This is due to the saturation voltage
GS
The MIC5190 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 regu-
lator are important. In cases where transient response is the
mostimportant,lowESR andlowESLceramiccapacitorsare
recommended. Also, themorecapacitanceontheoutput, the
better the transient response.
of the MIC5190 output driver.
≥ 2V + V + V
OUT
V
CC1,2
GS
For our example, with a 1.5V output voltage, our MOSFET is
fully enhanced at 4.5V , and so our V voltage should be
GS
CC
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 MIC5190. When a load transient on the
output occurs, the load step will also appear on the input.
VIN
J1
+VIN
330µF
16V
10µF 10µF
10µF
10Ω
100k
U1 MIC2198-BML
22µF
L1
1µF
25V
CSH
VOUT
VOUT
6
12
IRF7821
1.8µH
J2
EN
VIN
HSD
VSW
CDEP134-1R8MC-H
1VOUT @10A
10k
11
2
EN/UVLO
CSH
CSH
0.1µF
10µF
10µF
10Ω
4
10
BST
VOUT
VOUT
100pF
MIC5190
VCC1
100Ω
1µF
10Ω
10k
5
8
IRF7821
VOUT
FB
OUT
LSD
3
330µF
Tantalum
D2
VIN
VCC2
FB
D1
1N5819HW
SD103BWS
ISENSE
GND
1
7
COMP
VDD
COMP
560pF
GND
2.2µF
10V
100Ω
10nF
12.4k
9
11.5k
8.06k
Figure 9. Post Regulator
December 2005
10
M9999-120105
MICREL [ MICREL SEMICONDUCTOR ]
