MIC5190_04 Datasheet, PDF (10/13 Pages) Micrel Semiconductor – Ultra High-Speed, High-Current Active Filter/LDO Controller

MIC5190
Micrel
The gate-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_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 MIC5190 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, and so 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 MIC5190. 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
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.
Output Capacitor
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
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
330µF 10µF 10µF 10µF
16V
10Ω
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
5 _VOUT
3
FB
8
LSD
560pF
1 _COMP
VDD ⁷
GND
11.5k
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
22µF
10µF 10µF
1V_OUT @10A
MIC5190
OUT
VIN
VCC1
VCC2
ISENSE
GND
FB
COMP
10nF
12.4k
100Ω
1µF
100Ω
Figure 9. Post Regulator
December 2005
10
M9999-120105