MICREL MIC5158BN

MIC5156/5157/5158
Micrel
MIC5156/5157/5158
Super LDO™ Regulator Controller
General Description
The MIC5156, MIC5157, and MIC5158 Super Low-Dropout
(LDO) Regulator Controllers are single IC solutions for highcurrent low-dropout linear voltage regulation. Super LDO™
Regulators have the advantages of an external N-channel
power MOSFET as the linear pass element.
The MIC5156/7/8 family features a dropout voltage as low as
the RDS(ON) of the external power MOSFET multiplied by the
output current. The output current can be as high as the
largest MOSFETs can provide.
The MIC5156/7/8 family operates from 3V to 36V. The
MIC5156 requires an external gate drive supply to provide the
higher voltage needed to drive the gate of the external
MOSFET. The MIC5157 and MIC5158 each have an internal
charge pump tripler to produce the gate drive voltage. The
tripler is capable of providing enough voltage to drive a logiclevel MOSFET to 3.3V output from a 3.5V supply and is
clamped to 17.5V above the supply voltage. The tripler
requires three external capacitors.
The regulator output is constant-current limited when the
controller detects 35mV across an optional external sense
resistor. An active-low open-collector flag indicates a low
voltage of 8% or more below nominal output. A shutdown
(low) signal to the TTL-compatible enable control reduces
controller supply current to less than 1µA while forcing the
output voltage to ground.
The MIC5156-3.3 and MIC5156-5.0 controllers have internally fixed output voltages. The MIC5156 [adjustable] output
is configured using two external resistors. The MIC5157 is a
fixed output controller which is externally configured to select
either 3.3V, 5.0V, or 12V. The MIC5158 can be configured as
a fixed 5V controller or programmed to any voltage from 1.3V
to 36V using two external resistors.
The MIC5156 is available in an 8-pin DIP or SOP. The
MIC5157 and MIC5158 are available in a 14-pin DIP or SOP
which operate from –40°C to +85°C.
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
4.5mA typical operating current
<1µA typical standby current
Low external parts count
Optional current limit (35mV typical threshold)
1% initial output voltage tolerance in most configurations
2% output voltage tolerance over temperature
Fixed output voltages of 3.3V, 5.0V (MIC5156)
Fixed output voltages of 3.3V, 5.0V, 12V (MIC5157)
Programmable (1.3 to 36V) with 2 resistors (MIC5156/8)
Internal charge pump voltage tripler (MIC5157/8)
Enable pin to activate or shutdown the regulator
Internal gate-to-source protective clamp
All versions available in DIP and SOP
Applications
•
•
•
•
•
Ultrahigh current ultralow dropout voltage regulator
Constant high-current source
Low parts count 5.0V to 3.3V computer supply
Low noise/low-dropout SMPS post regulator
High-current, current-limited switch
Typical Applications
+12V
1.0µF
5V
VDD
C1–
C1+
8
8
9
10
11
12 13
0.1µF
3mΩ
VIN
5V
47µF
RS
RS = 0.035V / ILIMIT
SMP60N03-10L
1
3.3V
2
EN
3
S
EN
7
S
G
D
VDD
6
4
MIC5157
MIC5156-3.3
5
5
FLAG
FLAG
6
D
GND
7
GND
1
G
2
C2–
3
C2+
4
VCP
0.1µF
Enable
Shutdown
VP
0.1µF
CL*
47µF
VOUT
3.3V, 10A
VIN
(3.61V min.)
3mΩ
47µF
RS
RS = 0.035V / ILIMIT
* Improves transient
response to load changes
IRLZ44 (Logic Level MOSFET)
10A 5V to 3.3V Desktop Computer Regulator
14
Enable
Shutdown
CL*
47µF
VOUT
3.3V, 10A
* Improves transient
response to load changes
10A Low-Dropout Voltage Regulator
Super LDO is a trademark of Micrel, Inc.
3-112
March 1999
MIC5156/5157/5158
Micrel
Ordering Information MIC5156
Part Number
Temperature Range
Voltage
Package
MIC5156-3.3BN
–40°C to +85°C
3.3V
8-pin DIP
MIC5156-5.0BN
–40°C to +85°C
5.0V
8-pin DIP
MIC5156BN
–40°C to +85°C
Adjustable
8-pin DIP
MIC5156-3.3BM
–40°C to +85°C
3.3V
8-pin SOP
MIC5156-5.0BM
–40°C to +85°C
5.0V
8-pin SOP
MIC5156BM
–40°C to +85°C
Adjustable
8-pin SOP
Ordering Information MIC5157
Part Number
Temperature Range
Voltage
Package
MIC5157BN
–40°C to +85°C
Selectable
14-pin DIP
MIC5157BM
–40°C to +85°C
Selectable
14-pin SOP
Ordering Information MIC5158
Part Number
Temperature Range
Voltage
Package
MIC5158BN
–40°C to +85°C
5.0V/Adj.
14-pin DIP
MIC5158BM
–40°C to +85°C
5.0V/Adj.
14-pin SOP
Pin Configuration
MIC5156-x.x
EN 1
MIC5156
FLAG 2
7 D (Drain)
FLAG 2
7 D (Drain)
GND 3
6 G (Gate)
GND 3
6 G (Gate)
MIC5157
5V 1
3.3V 2
5 VD D
VP 4
5 VD D
VP 4
March 1999
8 EA
EN 1
8 S (Source)
MIC5158
EA 1
14 EN
14 EN
13 S (Source)
5V FB 2
13 S (Source)
FLAG 3
12 D (Drain)
FLAG 3
12 D (Drain)
GND 4
11 G (Gate)
GND 4
11 G (Gate)
VCP 5
10 VD D
VCP 5
10 VD D
C2– 6
9 C1–
C2– 6
9 C1–
C2+ 7
8 C1+
C2+ 7
8 C1+
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3
MIC5156/5157/5158
Micrel
Pin Description MIC5156
Pin Number
Pin Name
Pin Function
1
EN
2
FLAG
Output Flag (Output): Open collector output is active (low) when VOUT is more
than 8% below nominal output. Circuit has 3% hysteresis.
3
GND
Circuit ground.
4
VP
N-channel Gate Drive Supply Voltage: User supplied voltage for driving the
gate of the external MOSFET.
5
VDD
Supply Voltage (Input): Supply voltage connection. Connect sense resistor
(RS) to VDD if current limiting used. Connect supply bypass capacitor to
ground near device.
6
G
Gate (Output): Drives the gate of the external MOSFET.
7
D
Drain and Current Limit (Input): Connect to external MOSFET drain and
external sense resistor (current limit), or connect to VDD and external MOSFET
drain (no current limit).
8 (3.3V, 5V)
S
Source (Input): Top of internal resistive divider chain. Connect directly to the
load for best load regulation.
8 (adjustable)
EA
Enable (Input): TTL high enables regulator; TTL low shuts down regulator.
Error Amplifier (Input): Connect to external resistive divider.
Pin Description MIC5157, MIC5158
Pin Number
Pin Name
Pin Function
1 (MIC5157)
5V
5V Configuration (Input): Connect to S (source) pin for 5V output.
1 (MIC5158)
EA
Error Amplifier (Input): Connect to external resistive divider to obtain adjustable output.
2 (MIC5157)
3.3V
2 (MIC5158)
5V FB
5V Feedback (Input): Connect to EA for fixed 5V output.
3
FLAG
Output Voltage Flag (Output): Open collector is active (low) when VOUT is 8%
or more below its nominal value.
4
GND
Circuit ground.
5
VCP
Voltage Tripler Output [Filter Capacitor]. Connect a 1 to 10µF capacitor to ground.
6
C2–
Charge Pump Capacitor 2: Second stage of internal voltage tripler. Connect a
0.1µF capacitor from C2+ to C2–.
7
C2+
Charge Pump Capacitor 2: See C2– pin 6.
8
C1+
Charge Pump Capacitor 1: First stage of internal voltage tripler. Connect a
0.1µF capacitor from C1+ to C1–.
9
C1–
Charge Pump Capacitor 1: See C1+ pin 8.
10
VDD
Supply Voltage (Input): Supply voltage connection. Connect sense resistor
(RS) to VDD if current limiting used. Connect supply bypass capacitor to
ground near device.
11
G
Gate (Output): Connect to External MOSFET gate.
12
D
Drain and Current Limit (Input): Connect to external MOSFET drain and
external sense resistor (current limit), or connect to VDD and external MOSFET
drain (no current limit).
13 (MIC5157)
S
Source and 3.3V/5V Configuration: Top of internal resistor chain. Connect to
source of external MOSFET for 3.3V, 5V, and 12V operation. Also see 3.3V
and 5V pin descriptions.
13 (MIC5158)
S
Source (Input): Top of internal resistor chain. Connect to top of external
resistive divider and source of external MOSFET.
14
EN
3.3V Configuration (Input): Connect to S (source) pin for 3.3V output.
Enable (Input): TTL high enables regulator; TTL low shuts down regulator.
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March 1999
MIC5156/5157/5158
Micrel
Absolute Maximum Ratings (Note 1)
Operating Ratings (Note 2)
Supply Input (VDD) ...................................................... +38V
Enable Input (VEN) ......................................... –0.3V to 36V
Gate Output (VG) MIC5156 ......................................... +55V
Charge Pump Node (VCP) MIC5157/8 ........................ +55V
Source Connection (VS) .................................... 1.3 to +36V
Flag (VFLAG) .................................................... –0.3 to +40V
Storage Temperature (TS) ....................... –65°C to +150°C
Lead Temperature (soldering 10 sec.) ...................... 300°C
Ambient Temperature Range (TA)
MIC515xBM/BN ..................................... –40°C to +85°C
Junction Temperature (TJ) ...................................... +150°C
Thermal Resistance (θJA)
Package
MIC5156
MIC5157/8
DIP ............................... 100°C/W ..................... 90°C/W
SOP .............................. 160°C/W ................... 120°C/W
Electrical Characteristics
VDD = 5V, VEN = 5V; TA = 25°C; unless noted.
Symbol
Parameter
Condition
Min
VDD
Supply Voltage
IDD(ON)
IDD(OFF)
Supply Current MIC5156
Operating, VEN = 5V
Shutdown, VEN = 0V
IDD(ON)
IDD(OFF)
Supply Current MIC5157/8
Operating, VEN = 5V
Shutdown, VEN = 0V
VIH
VIL
Enable Input Threshold
High
Low
EN IB
Enable Input Bias Current
VEN = 2.4V
VCP
Max. Charge Pump Voltage
VCP – VDD, VDD > 10V
fCP
Charge Pump Frequency
VOUT MAX
Maximum Gate Drive Voltage
(MIC5157/8)
VSOURCE = 0V
VDD = 3.5V
VDD = 5V
VDD = 12V
VOUT MIN
Minimum Gate Drive Voltage
VSOURCE > VOUT(NOM)
VLIM
Current Limit Threshold
VDD – VD @ ILIM
VS
Source Voltage
Typ
Max
Units
36
V
2.7
0.1
10
5
mA
µA
4.5
0.1
10
5
mA
µA
1.3
1.3
0.8
V
V
20
25
µA
17.5
18.5
V
3
2.4
160
5
9
24
7.0
11.3
28
kHz
9
15
30
1.0
V
V
V
V
28
35
42
mV
Short G (gate) to (S) source, Note 4
MIC5156-3.3
MIC5156-5.0
MIC5157, 3.3V pin to S pin (3.3V config.)
MIC5157, 5V pin to S pin (5V config.)
MIC5157, VDD = 7V, (12V config.)
MIC5158, 5V FB pin to EA pin (5V config.)
3.267
4.950
3.250
4.950
11.70
4.925
3.3
5.0
3.3
5.0
12
5.0
3.333
5.050
3.350
5.050
12.30
5.075
V
V
V
V
V
V
1.222
1.235
1.248
V
2
7
mV
16.6
20
V
VBG
Bandgap Reference Voltage
MIC5156 [adjustable] and MIC5158
VLR
Output Voltage Line Regulation
5V < VDD < 15V, VOUT = 3.3V
VGS MAX
Gate to Source Clamp
VFT
Flag Comparator Threshold
% of nominal VSOURCE
92
%
VFH
Flag Comparator Hysteresis
% of nominal VSOURCE
3
%
VSAT
Flag Comparator Sat. Voltage
IFLAG = 1mA
14
0.09
Note 1.
Exceeding the absolute maximum rating may damage the device.
Note 2.
The device is not guaranteed to function outside its operating rating.
Note 3.
Devices are ESD sensitive. Handling precautions recommended.
Note 4.
Test configuration. External MOSFET not used.
March 1999
3-115
0.2
V
3
MIC5156/5157/5158
Micrel
Typical Characteristics
5.0V Regulator Output
Voltage vs. Temperature
3.33
5.03
10
3.31
3.30
3.29
3.28
3.27
MIC5157/8 On-State Supply
Current vs. Supply Voltage
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
0
5
10 15 20 25
SUPPLY VOLTAGE (V)
30
5.01
5.00
4.99
4.98
4.96
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
MIC5157/8 On-State Supply
Current vs. Temperature
5.0
4.5
4.0
3.5
3.0
2.5
VDD = 5V
2.0
1.5
1.0
0.5
0.0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
10
150
125
100
75
50
25
0
5
10 15 20 25
SUPPLY VOLTAGE (V)
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
30
Enable Threshold Voltage
vs. Temperature
Enable Input Bias Current
vs. Enable Voltage
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
120
ENABLE BIAS CURRENT (µA)
ENABLE THRESHOLD VOLTAGE (V)
0
VDD = 5V
IFLAG = 1mA
175
20
4
LOGIC
INPUT
2
3.3V
OUTPUT
100
80
60
40
20
0
0
2
4 6 8 10 12 14 16
ENABLE VOLTAGE (V)
3-116
0.0
0.2
0.4
TIME (ms)
0.6
Off-State Supply Current
vs. Temperature
5.0
4.5
VDD = 5V
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
Flag Output Voltage
vs. Flag Current
200
30
6
-2
-0.2
1.0
0.9
FLAG VOLTAGE (V)
60
40
8
Flag Output Voltage
vs. Temperature
FLAG VOLTAGE (mV)
CHARGE PUMP VOLTAGE (V)
Charge-Pump Output Voltage
vs. Supply Voltage
50
MOSFET = IRF540
VIN = 5V, IL = 0.5A
CC1 = CC2 = 0.1µF
CCP = 1µF
CL = 50µF
0
4.97
VDD = 5V
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
CURRENT LIMIT THRESHOLD (mV)
2.0
5.02
OFF-STATE SUPPLY CURRENT (µA)
3.32
VOLTAGE (V)
OUTPUT VOLTAGE (V)
12
3.26
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
ON-STATE SUPPLY CURRENT (mA)
MIC5157/8 Turn-On
Response Time for 3.3V
5.04
ON-STATE SUPPLY CURRENT (mA)
OUTPUT VOLTAGE (V)
3.3V Regulator Output
Voltage vs. Temperature
3.34
0
2
4
6
8
10
FLAG SINK CURRENT (mA)
Current Limit Threshold
vs. Temperature
70
60
50
40
30
20
10
0
-60 -30 0 30 60 90 120 150
TEMPERATURE (°C)
March 1999
MIC5156/5157/5158
Micrel
Block Diagram MIC5156
+12V Input
+5V Input
0.1µF
VP
VDD
Internal
Bias
EN
RS
3mΩ
Enable
Shutdown
12k
to all
internal blocks
ILIMIT
Comparator
D (Drain)
[ILIMIT]
35mV
1.235V
Bandgap
Reference
+5V Input
Q2
FLAG
G (Gate)
Error
Amp
16.6V
Q1
SMP60N03-10L
S* (Source)
Regulated
+3.3V Output
75mV
* fixed version only
3.3V = 17k, 5V = 32k
17k†
†
‡
10k
GND
CL
Load 1
Load 2
Switched
5V Load
VOUT
Comparator
3
EA‡
adjustable version only
Block Diagram with External Components
Fixed 3.3V Power Supply with 5.0V Load Switch
Block Diagram MIC5157
+5V Input
0.1µF
C1+
Oscillator
C1 0.1µF
C1–
C2+
C3
1µF
C2
C2–
VCP
VDD
VCP
Clamp
Charge Pump
Tripler
Internal
Bias
ILIMIT
Comparator
35mV
FLAG
RS
3mΩ
Enable
Shutdown
to all
internal blocks
1.235V
Bandgap
Reference
VOUT
Comparator
EN
D (Drain)
[ILIMIT]
G (Gate)
Error
Amp
16.6V
Q1
IRFZ44
S (Source)*
Regulated
+3.3V Output
75mV
58k
15k
5V
CL
3.3V
10k
Block Diagram with External Components
Fixed 3.3V 10A Power Supply
March 1999
3-117
Load
17k
GND
MIC5156/5157/5158
Micrel
Block Diagram MIC5158
+5V Input
0.1µF
C1+
Oscillator
C1 0.1µF
C1–
C2+
C3
1µF
C2
C2–
VCP
VDD
VCP
Clamp
Charge Pump
Tripler
Internal
Bias
ILIMIT
Comparator
35mV
FLAG
RS
3mΩ
Enable
Shutdown
to all
internal blocks
1.235V
Bandgap
Reference
VOUT
Comparator
EN
D (Drain)
[ILIMIT]
G (Gate)
Error
Amp
16.6V
Q1
IRFZ44
S (Source)
Regulated
+3.6V Output
32k
10k
5V
FB
CL
Load
75mV
GND
EA
19.1k
10.0k
Block Diagram with External Components
Adjustable Power Supply, 3.6V Configuration
Functional Description
A Super LDO Regulator is a complete regulator built around
Micrel’s Super LDO Regulator Controller.
Refer to Block Diagrams MIC5156, MIC5157, and MIC5158.
Version Differences
The MIC5156 requires an external voltage for MOSFET gate
drive and is available in 3.3V fixed output, 5V fixed output, or
adjustable output versions. With 8-pins, the MIC5156 is the
smallest of the Super LDO Regulator Controllers.
The MIC5157 and MIC5158 each have an internal charge
pump which provides MOSFET gate drive voltage. The
MIC5157 has a selectable fixed output of 3.3V, 5V, or 12V.
The MIC5158 may be configured for a fixed 5V or adjustable
output.
Enable (EN)
With at least 3.0V on VDD, applying a TTL low to EN places
the controller in shutdown mode. A TTL high on EN enables
the internal bias circuit which powers all internal circuitry. EN
must be pulled high if unused. The voltage applied to EN may
be as high as 36V.
The controller draws less than 1µA in shutdown mode.
Gate Enhancement
The Super LDO Regulator Controller manages the gate-tosource enhancement voltage for an external N-channel
MOSFET (regulator pass element) placed between the supply and the load. The gate-to-source voltage may vary from
1V to 16V depending upon the supply and load conditions.
Because the source voltage (output) approaches the drain
voltage (input) when the regulator is in dropout and the
MOSFET is fully enhanced, an additional higher supply
voltage is required to produce the necessary gate-to-source
enhancement. This higher gate drive voltage is provided by
an external gate drive supply (MIC5156) or by an internal
charge pump (MIC5157 and MIC5158).
Gate Drive Supply Voltage (MIC5156 only)
The gate drive supply voltage must not be more than 14V
above the supply voltage (VP – VDD < 14V). The minimum
necessary gate drive supply voltage is:
VP = VOUT + VGS + 1
where:
VP = gate drive supply voltage
VOUT = regulator output voltage
VGS = gate-to-source voltage for full
MOSFET gate enhancement
The error amplifier uses the gate drive supply voltage to drive
the gate of the external MOSFET. The error amplifier output
can swing to within 1V of VP.
3-118
March 1999
MIC5156/5157/5158
Micrel
Charge Pump (MIC5157/5158 only)
The charge pump tripler creates a dc voltage across reservoir
capacitor C3. External capacitors C1 and C2 provide the
necessary storage for the stages of the charge pump tripler.
The tripler’s approximate dc output voltage is:
VCP ≈ 3 (VDD – 1)
where:
VCP = charge pump output voltage
VDD = supply voltage
The VCP clamp circuit limits the charge pump voltage to 16V
above VDD by gating the charge pump oscillator ON or OFF
as required. The charge pump oscillator operates at 160kHz.
The error amplifier uses the charge pump voltage to drive the
gate of the external MOSFET. It provides a constant load of
about 1mA to the charge pump. The error amplifier output can
swing to within 1V of VCP.
Although the MIC5157/8 is designed to provide gate drive
using its internal charge pump, an external gate drive supply
voltage can be applied to VCP . When using an external gate
drive supply, VCP must not be forced more than 14V higher
than VDD.
When constant loads are driven, the ON/OFF switching of the
charge pump may be evident on the output waveform. This is
caused by the charge pump switching ON and rapidly increasing the supply voltage to the error amplifier. The period
of this small charge pump excitation is determined by a
number of factors: the input voltage, the 1mA op-amp load,
any dc leakage associated with the MOSFET gate circuit, the
size of the charge pump capacitors, the size of the charge
pump reservoir capacitor, and the characteristics of the input
voltage and load. The period is lengthened by increasing the
charge pump reservoir capacitor (C3). The amplitude is
reduced by weakening the charge pump—this is accomplished by reducing the size of the pump capacitors (C1 and
C2). If this small burst is a problem in the application, use a
10µF reservoir capacitor at C3 and 0.01µF pump capacitors
at C1 and C2. Note that the recovery time to repetitive load
transients may be affected with small pump capacitors.
Gate-to-Source Clamp
A gate-to-source protective voltage clamp of 16.6V protects
the MOSFET in the event that the output voltage is suddenly
forced to zero volts. This prevents damage to the external
MOSFET during shorted load conditions. Refer to “Charge
Pump” for normal clamp circuit operation.
The source connection required by the gate-to-source clamp
is not available on the adjustable version of the MIC5156.
Output Regulation
At start-up, the error amplifier feedback voltage (EA), or
internal feedback on fixed versions, is below nominal when
compared to the internal 1.235V bandgap reference. This
forces the error amplifier output high which turns on external
MOSFET Q1. Once the output reaches regulation, the controller maintains constant output voltage under changing
input and load conditions by adjusting the error amplifier
output voltage (gate enhancement voltage) according to the
feedback voltage.
Out-of-Regulation Detection
When the output voltage is 8% or more below nominal, the
open-collector FLAG output (normally high) is forced low to
signal a fault condition. The FLAG output can be used to
signal or control external circuitry. The FLAG output can also
be used to shut down the regulator using the EN control.
Current Limiting
Super LDO Regulators perform constant-current limiting (not
foldback). To implement current limiting, a sense resistor
(RS) must be placed in the “power” path between VDD and D
(drain).
If the voltage drop across the sense resistor reaches 35mV,
the current limit comparator reduces the error amplifier output. The error amplifier output is decreased only enough to
reduce the output current, keeping the voltage across the
sense resistor from exceeding 35mV.
Application Information
March 1999
3-119
VIN
G
MIC515x
GND
S
Load
MOSFET Selection
Standard N-channel enhancement-mode MOSFETs are acceptable for most Super LDO regulator applications.
Logic-level N-channel enhancement-mode MOSFETs may
be necessary if the external gate drive voltage is too low
(MIC5156), or the input voltage is too low, to provide adequate charge pump voltage (MIC5157/8) to enhance a
standard MOSFET.
Circuit Layout
For the best voltage regulation, place the source, ground, and
error amplifier connections as close as possible to the load.
See figures (1a) and (1b).
Figure 1a. Connections for Fixed Output
3
MIC5156/5157/5158
Micrel
Adjustable Configurations
Micrel’s MIC5156 [adjustable] and MIC5158 require an external resistive divider to set the output voltage from 1.235V to
36V. For best results, use a 10kΩ resistor for R2. See
equation (1) and figure (2).
VIN
G
S
Load
MIC5157
or
MIC5158
EA
GND
1)
V

R1 = 1× 104  OUT − 1
 1.235

G
VOUT
S
Figure 1b. Connections for Adjustable Output
MIC5157/8
GND
VIN
R1
EA*
R2
10k
G
*
MIC5156
EA
GND
Load
Figure 2. Typical Resistive Divider
Input Filter Capacitor
The Super LDO requires an input bypass capacitor for
accommodating wide changes in load current and for decoupling the error amplifier and charge pump. A medium to large
value low-ESR (equivalent series resistance) capacitor is
best, mounted close to the device.
* Optional 16V zener diode
recommended in applications
where VG is greater than 18V
Figure 1c. MIC5156 Connections for
Adjustable Output
MOSFET Gate-to-Source Protection
When using the adjustable version of the MIC5156, an
external 16V zener diode placed from gate-to-source is
recommended for MOSFET protection. All other versions of
the Super LDO regulator controller use the internal gate-tosource clamp.
Output Voltage Configuration
Fixed Configurations
The MIC5156-3.3 and MIC5156-5.0 are preset for 3.3V and
5.0V respectively.
The MIC5157 operates at 3.3V when the 3.3V pin is connected to the S (source) pin; 5.0V when the 5.0V pin is
connected to the S pin; or 12V if the 3.3V and 5.0V pins are
open.
The MIC5158 operates at a fixed 5V (without an external
resistive divider) if the 5V FB pin is connected to EA.
Output Filter Capacitor
An output filter capacitor may be used to reduce ripple and
improve load regulation. Stable operation does not require a
large capacitor, but for transient load regulation the size of the
output capacitor may become a consideration. Common
aluminum electrolytic capacitors perform nicely; very lowESR capacitors are not necessary. Increased capacitance
(rather than reduced ESR) is preferred. The capacitor value
should be large enough to provide sufficient I = C × dV/dt
current consistent with the required transient load regulation
quality. For a given step increase in load current, the output
voltage will drop by about dV = I × dt/C, where I represents the
increase in load current over time t. This relationship assumes that all output current was being supplied via the
MOSFET pass device prior to the load increase. Small
(0.01µF to 10µF) film capacitors parallel to the load will further
improve response to transient loads.
Some linear regulators specify a minimum required output
filter capacitance because the capacitor determines the
dominant pole of the system, and thereby stabilizes the
system. This is not the situation for the MIC5156/7/8; its
dominant pole is determined within its error amplifier.
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March 1999
MIC5156/5157/5158
Micrel
Current Limiting
Current sensing requires a low-value series resistance (Rs)
between VDD 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.
Gate Supply
Enable
Shutdown
VG
EN
VIN
RS
VDD
D
MIC5156-x.x G
RS =
35mV
ILIM
S
GND
Load
2)
where:
RS = sense resistor value
ILIM = 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 VDD and D (drain). See figure (3). The
controller will not limit current when it does not detect a 35mV
drop from VDD to D.
VIN
Figure 4a. High-Side Switch
If a MIC5157 or MIC5158 is used and is shutdown for a given
time, the charge pump reservoir VCP 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).
VIN
VDD
D
MIC5156 G
VDD
EN
G
S
MIC5158
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 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 currentlimited, 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.
EA
GND
Output Off
Output On
Load
S
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:
R1 

VFL = 1. 235  1 +


R2 
where:
VFL = float voltage
At float voltage, the MOSFET is shut off. A trickle charge is
supplied by R4.
March 1999
3-121
3
MIC5156/5157/5158
Micrel
VIN
R3
VDD
R4
D
EN
G
MIC5158
S
R1
EA
GND
R2
Figure 5. Battery Charger Concept
Uninterruptible Power Supply
The MIC5157 and two N-channel MOSFETs provide battery
switching for uninterruptible power as shown in figure (6).
Two MOSFETs are placed source-to-source to prevent current flow through their body diodes when switched off. The
Super LDO regulator is continuously enabled to achieve fast
battery switch-in. Careful attention must be paid to the ac-line
monitoring circuitry to ensure that the output voltage does not
fall below design limits while the battery is being switched in.
VDD
EN
D
Q1
G
D
G
S
MIC5158
S
S
MOSFET body diodes
shown for clarity
G
GND
Line
Battery
AC
Line
EA
Q2
D
40V max.
1N4148
Off-line
Power Supply
Uninterruptable
DC
Figure 6. UPS Power Supply Concept
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March 1999