MIC5156 Micrel Semiconductor, MIC5156 Datasheet - Page 10

• Manufacturer Part Number: MIC5156
• Description: Super LDO Regulator Controller
• Manufacturer: Micrel Semiconductor

Current Limiting
Current sensing requires a low-value series resistance (R
between V
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)
where:
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
controller will not limit current when it does not detect a 35mV
drop from V
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 supply
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
provide 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-
limited, 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.
March 1999
MIC5156/5157/5158
R
I
R
LIM
S
S
= sense resistor value
= maximum output current
=
DD
DD
35mV
and D (drain). Refer to the typical applications.
I
LIM
to D.
Figure 3. No Current Limit
DD
and D (drain). See figure (3). The
MIC5156
V
DD
G
D
S
V
IN
s
3-121
)
If a MIC5157 or MIC5158 is used and is shutdown for a given
time, the charge pump reservoir V
ing 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).
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
approaches the float voltage:
where:
At float voltage, the MOSFET is shut off. A trickle charge is
supplied by R4.
V
V
FL
FL
= float voltage
= 1. 235 1 +
Figure 4b. Fast High-Side Switch
Shutdown
Output Off
Output On
Enable
Figure 4a. High-Side Switch
Gate Supply
EN
MIC5156-x.x
EN
V
G
MIC5158
R2
R1
GND
GND
1N4148
V
V
DD
CP
DD
EA
G
D
S
G
S
will bleed off. If recharg-
R3) until the battery
V
IN
V
R
IN
S
Micrel
3