MIC5158YM Datasheet, PDF (10/13 Pages) Micrel Semiconductor – Super LDO Regulator Controller

MIC5156/5157/5158
Current Limiting
Current sensing requires a low-value series resistance (R_s)
between V_DD and D (drain). Refer to the typical applications.
The internal current-limiting circuit limits the voltage drop
across the sense resistor to 35mV. Equation (2) provides the
sense resistor value required for a given maximum current.
2)
R_S
=
35mV
I_LIM
where:
R_S = sense resistor value
I_LIM = maximum output current
Most current-limited applications require low-value resistors.
See Application Hints 21 and 25 for construction hints.
Non-Current-Limited Applications
For circuits not requiring current limiting, do not use a sense
resistor between V_DD and D (drain). See figure (3). The con-
troller will not limit current when it does not detect a 35mV
drop from V_DD to D.
V_IN
Gate Supply
Enable
Shutdown
V_G
EN
V_DD
D
MIC5156-x.xG
S
GND
Micrel, Inc.
V_IN
R_S
Figure 4a. High-Side Switch
If a MIC5157 or MIC5158 is used and is shutdown for a
given time, the charge pump reservoir V_CP will bleed off. If
recharging the reservoir causes an unacceptable delay in the
load reaching its operating voltage, do not use the EN pin
for on/off control. Instead, use the MIC5158, hold EN high to
keep the charge pump in continuous operation, and switch
the MOSFET on or off by overriding the error amplifier input
as shown in figure (4b).
V_IN
V_DD
D
MIC5156 G
S
Figure 3. No Current Limit
3.3V Microprocessor Applications
For computer designs that use 3.3V microprocessors with 5V
logic, the FLAG output can be used to suppress the 5V sup-
ply until the 3.3V output is in regulation. Refer to the external
components shown with the MIC5156 Block Diagram.
SMPS Post Regulator Application
A Super LDO regulator can be used as a post regulator for a
switch-mode power supply. The Super LDO regulator can pro-
vide a significant reduction in peak-to-peak ripple voltage.
High-Current Switch Application
All versions of the MIC5156/7/8 may be used for current-lim-
ited, high-current, high-side switching with or without voltage
regulation. See figure (4a). Simply leave the “S” terminal
open. A 16V zener diode from the gate to the source of the
MOSFET protects the MOSFET from overdrive during fault
conditions.
V_DD
EN
G
MIC5158 ^S
EA
GND
Output Off
Output On
1N4148
Figure 4b. Fast High-Side Switch
Battery Charger Application
The MIC5158 may be used in constant-current applications
such as battery chargers. See figure (5). The regulator supplies
a constant-current (35mV ÷ R3) until the battery approaches
the float voltage:
( ) V _FL = 1 . 2 3 5
1
+
R1
R2
where:
V_FL = float voltage
At float voltage, the MOSFET is shut off. A trickle charge is
supplied by R4.
MIC5156/5157/5158
10
August 2005