MIC5191 Datasheet, PDF (10/13 Pages) Micrel Semiconductor – Ultra High-Speed, High-Current Active Filter/LDO Controller

MIC5191
ource threshold specified in most MOSFET data sheets
refers to the minimumvoltage needed to fully enhance the
MOSFET. Although for the most part, the MOSFET will be
operating in the linear region and the V_GS (gate-source
voltage) will be less than the fully enhanced V_GS, it is
recommended the V_CC voltage has 2V over the minimum
V_GS and output voltage. This is due to the saturation
voltage of the MIC5191 output driver.
V_CC1,2 ≥ 2V + V_GS + V_OUT
For our example, with a 1.5V output voltage, our MOSFET is
fully enhanced at 4.5V_GS, our V_CC voltage 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
Micrel
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, but for optimal
performance it is 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 regu-
lator 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.
V_IN
J1
+V_IN
12V
330µF 10µF 10µF 10µF
16V
100k
1µF
J2
25V
EN
CSH _10Ω
U1 MIC2198-BML
6
VIN
2 _EN/UVLO
4
CSH
12
HSD
11
VSW
10
BST
IRF7821
0.1µF
V_OUT
V_OUT
100pF
10Ω
10k
560pF
11.5k
5 _VOUT
3
FB
8
LSD
1 _COMP
VDD ⁷
GND
9
8.06k
IRF7821
D1
SD103BWS
2.2µF
10V
L1
1.8µH
CSH
V_OUT
CDEP134-1R8MC-H
10k
V_OUT
D2
1N5819HW
330µF
Tantalum
10Ω
22µF
10µF 10µF
1V_OUT @10A
MIC5191
OUT
VIN
ISENSE
GND
VCC1
VCC2
FB
COMP
10nF
12.4k
100Ω
1µF
Figure 9. Post Regulator
April 2004
10
M9999-042804