MIC5156BN [MICREL]
Super LDO⑩ Regulator Controller; 超级LDO ™稳压器控制器
| 型号： | MIC5156BN |
| 厂家： | 
MICREL SEMICONDUCTOR |
| 描述： | Super LDO⑩ Regulator Controller |
| 文件： | 总11页 (文件大小：96K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MIC5156/5157/5158
Super LDO™ Regulator Controller
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.
General Description
The MIC5156, MIC5157, and MIC5158 Super Low-Dropout
(LDO) Regulator Controllers are single IC solutions for high-
current 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 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.
The MIC5156/7/8 family features a dropout voltage as low as
the R
of the external power MOSFET multiplied by the
DS(ON)
Features
• 4.5mA typical operating current
• <1µA typical standby current
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
MIC5156requiresanexternalgatedrivesupplytoprovidethe
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 logic-
level 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.
• 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
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.
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
The MIC5156-3.3 and MIC5156-5.0 controllers have inter-
nally 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
Typical Applications
+12V
1.0µF
0.1µF
0.1µF
Enable
Shutdown
7
6
5
4
3
2
1
4
3
2
1
MIC5157
MIC5156-3.3
8
9
10 11 12 13 14
5
6
7
8
0.1µF
Enable
3mΩ
Shutdown
3mΩ
RS
VOUT
3.3V, 10A
VIN
5V
VOUT
3.3V, 10A
VIN
RS
(3.61V min.)
CL*
47µF
CL*
47µF
47µF
47µF
RS = 0.035V / ILIMIT
IRLZ44 (Logic Level MOSFET)
RS = 0.035V / ILIMIT
*Improves transient
response to load changes
*Improves transient
response to load changes
SMP60N03-10L
10A 5V to 3.3V Desktop Computer Regulator
10A Low-Dropout Voltage Regulator
Super LDO is a trademark of Micrel, Inc.
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March 1999
MIC5156/5157/5158
Micrel
Ordering Information MIC5156
Part Number
MIC5156-3.3BN
MIC5156-5.0BN
MIC5156BN
Temperature Range
Voltage
3.3V
Package
8-pin DIP
8-pin DIP
8-pin DIP
8-pin SOP
8-pin SOP
8-pin SOP
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
5.0V
Adjustable
3.3V
MIC5156-3.3BM
MIC5156-5.0BM
MIC5156BM
5.0V
Adjustable
Ordering Information MIC5157
Part Number
MIC5157BN
MIC5157BM
Temperature Range
–40°C to +85°C
Voltage
Selectable
Selectable
Package
14-pin DIP
14-pin SOP
–40°C to +85°C
Ordering Information MIC5158
Part Number
MIC5158BN
MIC5158BM
Temperature Range
Voltage
5.0V/Adj.
5.0V/Adj.
Package
14-pin DIP
14-pin SOP
–40°C to +85°C
–40°C to +85°C
3
Pin Configuration
MIC5156-x.x
MIC5156
EN 1
8
EA
EN 1
8
7
6
5
S (Source)
D (Drain)
G (Gate)
VD D
FLAG 2
GND 3
7
6
5
D (Drain)
G (Gate)
VD D
FLAG 2
GND 3
VP
4
VP
4
MIC5157
MIC5158
5V 1
3.3V 2
14 EN
EA 1
5V FB 2
FLAG 3
GND 4
14 EN
13 S (Source)
12 D (Drain)
11 G (Gate)
10 VD D
13 S (Source)
12 D (Drain)
11 G (Gate)
10 VD D
FLAG 3
GND 4
VCP
5
VCP 5
C2– 6
C2+ 7
9
8
C1–
C1+
C2– 6
C2+ 7
9
8
C1–
C1+
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Pin Description MIC5156
Pin Number
Pin Name
Pin Function
1
2
EN
Enable (Input): TTL high enables regulator; TTL low shuts down regulator.
FLAG
Output Flag (Output): Open collector output is active (low) when VOUT is more
than 8% below nominal output. Circuit has 3% hysteresis.
3
4
GND
VP
Circuit ground.
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
7
G
D
Gate (Output): Drives the gate of the external MOSFET.
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
Error Amplifier (Input): Connect to external resistive divider.
Pin Description MIC5157, MIC5158
Pin Number
1 (MIC5157)
1 (MIC5158)
Pin Name
Pin Function
5V
EA
5V Configuration (Input): Connect to S (source) pin for 5V output.
Error Amplifier (Input): Connect to external resistive divider to obtain adjust-
able output.
2 (MIC5157)
2 (MIC5158)
3
3.3V
5V FB
FLAG
3.3V Configuration (Input): Connect to S (source) pin for 3.3V output.
5V Feedback (Input): Connect to EA for fixed 5V output.
Output Voltage Flag (Output): Open collector is active (low) when VOUT is 8%
or more below its nominal value.
4
5
6
GND
VCP
C2–
Circuit ground.
Voltage Tripler Output [Filter Capacitor]. Connect a 1 to 10µF capacitor to ground.
Charge Pump Capacitor 2: Second stage of internal voltage tripler. Connect a
0.1µF capacitor from C2+ to C2–.
7
8
C2+
C1+
Charge Pump Capacitor 2: See C2– pin 6.
Charge Pump Capacitor 1: First stage of internal voltage tripler. Connect a
0.1µF capacitor from C1+ to C1–.
9
C1–
VDD
Charge Pump Capacitor 1: See C1+ pin 8.
10
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
12
G
D
Gate (Output): Connect to External MOSFET gate.
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)
14
S
Source (Input): Top of internal resistor chain. Connect to top of external
resistive divider and source of external MOSFET.
EN
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 (V ) ......................................................+38V
Ambient Temperature Range (T )
DD
A
MIC515xBM/BN ..................................... –40°C to +85°C
Enable Input (V ) ......................................... –0.3V to 36V
EN
Junction Temperature (T ) ...................................... +150°C
Gate Output (V ) MIC5156 .........................................+55V
J
G
Thermal Resistance (θ
Package
)
Charge Pump Node (V ) MIC5157/8 ........................+55V
JA
CP
MIC5156
MIC5157/8
Source Connection (V ) ....................................1.3 to +36V
S
DIP ............................... 100°C/W .....................90°C/W
SOP.............................. 160°C/W ................... 120°C/W
Flag (V
) ....................................................–0.3 to +40V
FLAG
Storage Temperature (T ) ....................... –65°C to +150°C
S
Lead Temperature (soldering 10 sec.) ...................... 300°C
Electrical Characteristics
VDD = 5V, VEN = 5V; TA = 25°C; unless noted.
Symbol
Parameter
Condition
Min
Typ
Max
Units
VDD
Supply Voltage
3
36
V
IDD(ON)
IDD(OFF)
Supply Current MIC5156
Operating, VEN = 5V
Shutdown, VEN = 0V
2.7
0.1
10
5
mA
µA
3
IDD(ON)
IDD(OFF)
Supply Current MIC5157/8
Enable Input Threshold
Operating, VEN = 5V
Shutdown, VEN = 0V
4.5
0.1
10
5
mA
µA
VIH
VIL
High
Low
2.4
1.3
1.3
V
V
0.8
25
EN IB
VCP
fCP
Enable Input Bias Current
Max. Charge Pump Voltage
Charge Pump Frequency
VEN = 2.4V
20
µA
V
VCP – VDD, VDD > 10V
17.5
160
18.5
kHz
VOUT MAX Maximum Gate Drive Voltage
(MIC5157/8)
VSOURCE = 0V
VDD = 3.5V
VDD = 5V
5
9
24
7.0
11.3
28
9
15
30
V
V
V
VDD = 12V
VOUT MIN
VLIM
Minimum Gate Drive Voltage
Current Limit Threshold
Source Voltage
VSOURCE > VOUT(NOM)
VDD – VD @ ILIM
1.0
35
V
28
42
mV
VS
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
3.333
5.050
3.350
5.050
12.30
5.075
V
V
V
V
V
V
5.0
VBG
Bandgap Reference Voltage
MIC5156 [adjustable] and MIC5158
1.222 1.235 1.248
V
mV
V
VLR
Output Voltage Line Regulation 5V < VDD < 15V, VOUT = 3.3V
Gate to Source Clamp
2
16.6
92
7
VGS MAX
VFT
14
20
Flag Comparator Threshold
Flag Comparator Hysteresis
Flag Comparator Sat. Voltage
% of nominal VSOURCE
% of nominal VSOURCE
IFLAG = 1mA
%
%
V
VFH
3
VSAT
0.09
0.2
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
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MIC5156/5157/5158
Micrel
Typical Characteristics
3.3V Regulator Output
Voltage vs. Temperature
5.0V Regulator Output
Voltage vs. Temperature
MIC5157/8 Turn-On
Response Time for 3.3V
3.34
5.04
5.03
5.02
5.01
5.00
4.99
4.98
4.97
4.96
12
10
8
MOSFET = IRF540
IN = 5V, IL = 0.5A
CC1 = CC2 = 0.1µF
CCP = 1µF
L = 50µF
3.33
3.32
3.31
3.30
3.29
3.28
3.27
3.26
V
6
C
4
LOGIC
INPUT
2
3.3V
OUTPUT
0
-2
-0.2
-60 -30
0
30 60 90 120 150
-60 -30
0
30 60 90 120 150
0.0
0.2
TIME (ms)
0.4
0.6
TEMPERATURE (°C)
TEMPERATURE (°C)
MIC5157/8 On-State Supply
Current vs. Supply Voltage
MIC5157/8 On-State Supply
Current vs. Temperature
Off-State Supply Current
vs. Temperature
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
VDD = 5V
VDD = 5V
0
5
10 15 20 25 30
-60 -30
0
30 60 90 120 150
-60 -30
0
30 60 90 120 150
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
TEMPERATURE (°C)
Charge-Pump Output Voltage
vs. Supply Voltage
Flag Output Voltage
vs. Temperature
Flag Output Voltage
vs. Flag Current
60
200
175
150
125
100
75
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
VDD = 5V
FLAG = 1mA
VDD = 5V
50
40
30
20
10
0
I
50
25
0
0
5
10 15 20 25 30
-60 -30
0
30 60 90 120 150
0
2
4
6
8
10
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
FLAG SINK CURRENT (mA)
Enable Threshold Voltage
vs. Temperature
Enable Input Bias Current
vs. Enable Voltage
Current Limit Threshold
vs. Temperature
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
120
100
80
60
40
20
0
70
60
50
40
30
20
10
0
-60 -30
0
30 60 90 120 150
0
2
4
6
8
10 12 14 16
-60 -30
0
30 60 90 120 150
TEMPERATURE (°C)
ENABLE VOLTAGE (V)
TEMPERATURE (°C)
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March 1999
MIC5156/5157/5158
Micrel
Block Diagram MIC5156
+12V Input
+5V Input
0.1µF
VP
VDD
EN
Internal
Bias
Enable
Shutdown
RS
3mΩ
12k
to all
internal blocks
1.235V
Bandgap
ILIMIT
Reference
Comparator
D (Drain)
[ILIMIT
+5V Input
Q2
]
35mV
16.6V
G (Gate)
VOUT
Comparator
Q1
Error
Amp
SMP60N03-10L
FLAG
Switched
S* (Source)
Regulated
+3.3V Output
5V Load
75mV
17k†
10k
* fixed version only
† 3.3V = 17k, 5V = 32k
CL
GND
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
C3
1µF
0.1µF C1 0.1µF C2
C1+ C1– C2+ C2–
VCP
VDD
EN
VCP
Clamp
Internal
Bias
Charge Pump
Tripler
Enable
Shutdown
RS
3mΩ
Oscillator
to all
internal blocks
1.235V
Bandgap
Reference
ILIMIT
Comparator
D (Drain)
[ILIMIT
]
35mV
16.6V
G (Gate)
VOUT
Error
Q1
IRFZ44
Amp
Comparator
FLAG
S (Source)*
Regulated
+3.3V Output
75mV
58k
15k
17k
10k
5V
CL
3.3V
GND
Block Diagram with External Components
Fixed 3.3V 10A Power Supply
March 1999
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MIC5156/5157/5158
Micrel
Block Diagram MIC5158
+5V Input
C3
1µF
0.1µF C1 0.1µF C2
C1+ C1– C2+ C2–
VCP
VDD
EN
VCP
Clamp
Internal
Bias
Charge Pump
Tripler
Enable
Shutdown
RS
3mΩ
Oscillator
to all
internal blocks
1.235V
Bandgap
Reference
ILIMIT
Comparator
D (Drain)
[ILIMIT
]
35mV
16.6V
G (Gate)
VOUT
Comparator
Error
Amp
Q1
IRFZ44
FLAG
S (Source)
Regulated
+3.6V Output
75mV
5V
FB
32k
10k
CL
GND
19.1k
10.0k
EA
Block Diagram with External Components
Adjustable Power Supply, 3.6V Configuration
MOSFET (regulator pass element) placed between the sup-
ply and the load. The gate-to-source voltage may vary from
1V to 16V depending upon the supply and load conditions.
Functional Description
A Super LDO Regulator is a complete regulator built around
Micrel’s Super LDO Regulator Controller.
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).
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.
Gate Drive Supply Voltage (MIC5156 only)
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.
The gate drive supply voltage must not be more than 14V
above the supply voltage (V – V < 14V). The minimum
P
DD
necessary gate drive supply voltage is:
V = V + V + 1
P
OUT
GS
Enable (EN)
where:
V = gate drive supply voltage
With at least 3.0V on V , applying a TTL low to EN places
DD
P
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.
V
V
= regulator output voltage
OUT
= gate-to-source voltage for full
GS
MOSFET gate enhancement
The error amplifier uses the gate drive supply voltage to drive
the gate of the external MOSFET. The error amplifier output
The controller draws less than 1µA in shutdown mode.
Gate Enhancement
can swing to within 1V of V .
P
The Super LDO Regulator Controller manages the gate-to-
source enhancement voltage for an external N-channel
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Micrel
Charge Pump (MIC5157/5158 only)
at C1 and C2. Note that the recovery time to repetitive load
transients may be affected with small pump capacitors.
Thechargepumptriplercreatesadcvoltageacrossreservoir
capacitor C3. External capacitors C1 and C2 provide the
necessary storage for the stages of the charge pump tripler.
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 tripler’s approximate dc output voltage is:
V
≈ 3 (V – 1)
CP
DD
where:
V
V
= charge pump output voltage
= supply voltage
CP
The source connection required by the gate-to-source clamp
is not available on the adjustable version of the MIC5156.
DD
The V clamp circuit limits the charge pump voltage to 16V
Output Regulation
CP
above V by gating the charge pump oscillator ON or OFF
DD
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 con-
troller 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.
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
about1mAtothechargepump.Theerroramplifieroutputcan
swing to within 1V of V
.
CP
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 V . When using an external gate
CP
drive supply, V must not be forced more than 14V higher
Out-of-Regulation Detection
CP
3
than V
.
DD
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.
Whenconstantloadsaredriven, theON/OFFswitchingofthe
charge pump may be evident on the output waveform. This is
caused by the charge pump switching ON and rapidly in-
creasing 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 accom-
plished 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
Current Limiting
Super LDO Regulators perform constant-current limiting (not
foldback). To implement current limiting, a sense resistor
(R ) must be placed in the “power” path between V and D
S
DD
(drain).
If the voltage drop across the sense resistor reaches 35mV,
the current limit comparator reduces the error amplifier out-
put. 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
MOSFET Selection
VIN
Standard N-channel enhancement-mode MOSFETs are ac-
ceptable for most Super LDO regulator applications.
G
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 ad-
equate charge pump voltage (MIC5157/8) to enhance a
standard MOSFET.
S
MIC515x
GND
Circuit Layout
Forthebestvoltageregulation,placethesource,ground,and
error amplifier connections as close as possible to the load.
See figures (1a) and (1b).
Figure 1a. Connections for Fixed Output
March 1999
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Micrel
Adjustable Configurations
VIN
Micrel’sMIC5156[adjustable]andMIC5158requireanexter-
nal 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).
G
S
MIC5157
or
MIC5158
VOUT
R1 = 1×104
− 1
EA
1)
GND
1.235
G
S
VOUT
Figure 1b. Connections for Adjustable Output
R1
MIC5157/8
EA*
GND
VIN
R2
10k
G
*
MIC5156
Figure 2. Typical Resistive Divider
EA
GND
Input Filter Capacitor
The Super LDO requires an input bypass capacitor for
accommodating wide changes in load current and for decou-
pling 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
Output Filter Capacitor
An output filter capacitor may be used to reduce ripple and
improve load regulation. Stable operation does not require a
largecapacitor,butfortransientloadregulationthesizeofthe
output capacitor may become a consideration. Common
aluminum electrolytic capacitors perform nicely; very low-
ESR 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
voltagewilldropbyaboutdV=I× dt/C, whereIrepresentsthe
increase in load current over time t. This relationship as-
sumes that all output current was being supplied via the
MOSFET pass device prior to the load increase. Small
(0.01µFto10µF)filmcapacitorsparalleltotheloadwillfurther
improve response to transient loads.
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-to-
source 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 con-
nected 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.
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.
The MIC5158 operates at a fixed 5V (without an external
resistive divider) if the 5V FB pin is connected to EA.
3-120
March 1999
MIC5156/5157/5158
Micrel
Current Limiting
Gate Supply
VIN
Current sensing requires a low-value series resistance (R )
s
between V and D (drain). Refer to the typical applications.
DD
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.
RS
VG
VDD
Enable
Shutdown
EN
D
G
S
MIC5156-x.x
35mV
2)
R
=
S
GND
I
LIM
where:
R = sense resistor value
S
I
= maximum output current
LIM
Most current-limited applications require low-value resistors.
See Application Hints 21 and 25 for construction hints.
Figure 4a. High-Side Switch
If a MIC5157 or MIC5158 is used and is shutdown for a given
Non-Current-Limited Applications
time, the charge pump reservoir V will bleed off. If recharg-
CP
For circuits not requiring current limiting, do not use a sense
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).
resistor between V
and D (drain). See figure (3). The
DD
controller will not limit current when it does not detect a 35mV
drop from V to D.
DD
VIN
3
VIN
VDD
D
G
S
MIC5156
VDD
EN
G
S
MIC5158
Figure 3. No Current Limit
3.3V Microprocessor Applications
EA
GND
Forcomputerdesignsthatuse3.3Vmicroprocessorswith5V
logic, theFLAGoutputcanbeusedtosuppressthe5Vsupply
until the 3.3V output is in regulation. Refer to the external
components shown with the MIC5156 Block Diagram.
1N4148
Output Off
Output On
Figure 4b. Fast High-Side Switch
Battery Charger Application
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
provideasignificantreductioninpeak-to-peakripplevoltage.
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:
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.
R1
V
= 1.235 1 +
FL
R2
where:
V
= float voltage
FL
At float voltage, the MOSFET is shut off. A trickle charge is
supplied by R4.
March 1999
3-121
MIC5156/5157/5158
Micrel
VIN
R3
R4
VDD
D
G
S
EN
MIC5158
R1
R2
EA
GND
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 cur-
rent flow through their body diodes when switched off. The
Super LDO regulator is continuously enabled to achieve fast
batteryswitch-in. Carefulattentionmustbepaidtotheac-line
monitoringcircuitrytoensurethattheoutputvoltagedoesnot
fall below design limits while the battery is being switched in.
VDD
EN
D
G
S
D
Q1
G
S
S
MOSFET body diodes
shown for clarity
MIC5158
G
Q2
D
EA
GND
40V max.
1N4148
Line
Battery
AC
Line
Uninterruptable
DC
Off-line
Power Supply
Figure 6. UPS Power Supply Concept
3-122
March 1999
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