LP3856-ADJ_15 [TI]
3A Fast Response Ultra Low Dropout Linear Regulators;
| 型号： | LP3856-ADJ_15 |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | 3A Fast Response Ultra Low Dropout Linear Regulators |
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LP3856-ADJ
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SNVS243E –SEPTEMBER 2003–REVISED APRIL 2013
LP3856-ADJ 3A Fast Response Ultra Low Dropout Linear Regulators
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1
FEATURES
DESCRIPTION
The LP3856-ADJ fast ultra low-dropout linear
regulators operate from a +2.5V to +7.0V input
supply. These ultra low dropout linear regulators
respond very quickly to step changes in load, which
makes them suitable for low voltage microprocessor
applications. The LP3856-ADJ is developed on a
CMOS process which allows low quiescent current
operation independent of output load current. This
CMOS process also allows the LP3856-ADJ to
operate under extremely low dropout conditions.
2
•
•
•
•
•
•
•
Ultra Low Dropout Voltage
Stable with Selected Ceramic Capacitors
Low Ground Pin Current
Load Regulation of 0.08%
10nA Quiescent Current in Shutdown Mode
Specified Output Current of 3A DC
Available in DDPAK/TO-263 and TO-220
Packages
•
•
Overtemperature/Overcurrent Protection
Dropout Voltage: Ultra low dropout voltage; typically
39mV at 300mA load current and 390mV at 3A load
current.
−40°C to +125°C Junction Temperature Range
APPLICATIONS
Ground Pin Current: Typically 4mA at 3A load
current.
•
•
•
•
•
•
•
•
Microprocessor Power Supplies
GTL, GTL+, BTL, and SSTL Bus Terminators
Power Supplies for DSPs
SCSI Terminator
Shutdown Mode: Typically 10nA quiescent current
when the shutdown pin is pulled low.
Adjustable Output Voltage: The output voltage may
be programmed via two external resistors.
Post Regulators
High Efficiency Linear Regulators
Battery Chargers
Other Battery Powered Applications
TYPICAL APPLICATION CIRCUIT
OUTPUT
3A
VIN
VOUT
INPUT
CFF**
R1**
LP3856-ADJ
SD **
ADJ
SD
GND
*COUT
10 mF
*CIN
10 mF
R2**
* TANTALUM OR
CERAMIC
R1
R2
)
VOUT = 1.216 x (1+
**See Application Hints
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
2
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2003–2013, Texas Instruments Incorporated
LP3856-ADJ
SNVS243E –SEPTEMBER 2003–REVISED APRIL 2013
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
CONNECTION DIAGRAM
Figure 1. TO-220-5 Package (Top View)
Bent, Staggered Leads
Figure 2. DDPAK/TO-263-5 Package (Top View)
PIN DESCRIPTION for TO-220-5 and DDPAK/TO-263-5 Packages
Pin #
LP3856-ADJ
Name
SD
Function
1
2
3
4
5
Shutdown
VIN
Input Supply
Ground
GND
VOUT
ADJ
Output Voltage
Set Output Voltage
BLOCK DIAGRAM
LP3856-ADJ
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(1)
ABSOLUTE MAXIMUM RATINGS
VALUE / UNITS
Storage Temperature Range
Lead Temperature
−65°C to +150°C
(Soldering, 5 sec.)
260°C
2 kV
(2)
ESD Rating
(3)
Power Dissipation
Internally Limited
−0.3V to +7.5V
−0.3V to 7.5V
−0.3V to +6.0V
Short Circuit Protected
Input Supply Voltage (Survival)
Shutdown Input Voltage (Survival)
(4) (5)
Output Voltage (Survival),
IOUT (Survival)
,
(1) Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions for which
the device is intended to be functional, but does not ensure specific performance limits. For specifications and test conditions, see
Electrical Characteristics. The specifications apply only for the test conditions listed. Some performance characteristics may degrade
when the device is not operated under the listed test conditions.
(2) The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin.
(3) At elevated temperatures, devices must be derated based on package thermal resistance. The devices in TO-220 package must be
derated at θjA = 50°C/W (with 0.5in2, 1oz. copper area), junction-to-ambient (with no heat sink). The devices in the DDPAK/TO-263
surface-mount package must be derated at θjA = 60°C/W (with 0.5in2, 1oz. copper area), junction-to-ambient. See Application Hints.
(4) If used in a dual-supply system where the regulator load is returned to a negative supply, the output must be diode-clamped to ground.
(5) The output PMOS structure contains a diode between the VIN and VOUT terminals. This diode is normally reverse biased. This diode will
get forward biased if the voltage at the output terminal is forced to be higher than the voltage at the input terminal. This diode can
typically withstand 200mA of DC current and 1Amp of peak current.
RECOMMENDED OPERATING CONDITIONS
VALUE / UNITS
(1)
Input Supply Voltage (Operating),
Shutdown Input Voltage (Operating)
Maximum Operating Current (DC)
Operating Junction Temp. Range
2.5V to 7.0V
−0.3V to 7.0V
3A
−40°C to +125°C
(1) The minimum operating value for VIN is equal to either [VOUT(NOM) + VDROPOUT] or 2.5V, whichever is greater.
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ELECTRICAL CHARACTERISTICS — LP3856-ADJ
Limits in standard typeface are for TJ = 25°C, and limits in boldface type apply over the full operating temperature range.
Unless otherwise specified: VIN = VO(NOM) + 1V, IL = 10 mA, COUT = 10µF, VSD = 2V.
LP3856-ADJ(2)
(1)
Symbol
Parameter
Adjust Pin Voltage
Conditions
Typ
Units
Min
Max
1.198
1.234
VADJ
IADJ
VOUT +1V ≤ VIN≤ 7V, 10 mA ≤ IL ≤ 3A
VOUT +1V ≤ VIN≤ 7V, 10 mA ≤ IL ≤ 3A
VOUT +1V ≤ VIN≤ 7.0V
1.216
10
V
nA
%
1.180
1.253
Adjust Pin Input Current
100
0.02
0.06
(3)
ΔV OL
Output Voltage Line Regulation
ΔVO/
ΔIOUT
0.08
0.14
Output Voltage Load Regulation(3)
10 mA ≤ IL ≤ 3A
IL = 300 mA
IL = 3A
%
55
75
39
390
4
VIN - VOUT Dropout Voltage(4)
mV
500
700
9
10
IL = 300 mA
IL = 3A
Ground Pin Current In Normal
Operation Mode
IGND
mA
9
10
4
V
SD ≤ 0.3V
-40°C ≤ TJ ≤ 85°C
O ≥ VO(NOM) - 4%
0.01
10
Ground Pin Current In Shutdown
Mode
IGND
µA
A
50
IO(PK)
Peak Output Current
V
4.5
6
Short Circuit Protection
ISC
Short Circuit Current
A
Shutdown Input
VSDT Rising from 0.3V until Output = ON
1.3
1.3
20
25
1
2
VSDT
Shutdown Threshold
V
VSDT Falling from 2.0V until Output = OFF
0.3
TdOFF
TdON
ISD
Turn-off delay
Turn-on delay
SD Input Current
IL = 3A
µs
µs
nA
IL = 3A
VSD = VIN
AC Parameters
VIN = VOUT + 1V, COUT = 10uF
VOUT = 3.3V, f = 120Hz
73
57
PSRR
Ripple Rejection
dB
µV
VIN = VOUT + 0.5V, COUT = 10uF
VOUT = 3.3V, f = 120Hz
ρn(l/f
Output Noise Density
Output Noise Voltage
f = 120Hz
0.8
150
100
BW = 10Hz – 100kHz, VOUT = 2.5V
BW = 300Hz – 300kHz, VOUT = 2.5V
µV
(rms)
en
(1) Typical numbers are at 25°C and represent the most likely parametric norm.
(2) Limits are verified by testing, design, or statistical correlation.
(3) Output voltage line regulation is defined as the change in output voltage from the nominal value due to change in the input line voltage.
Output voltage load regulation is defined as the change in output voltage from the nominal value due to change in load current.
(4) Dropout voltage is defined as the minimum input to output differential voltage at which the output drops 2% below the nominal value.
Dropout voltage specification applies only to output voltages of 2.5V and above. For output voltages below 2.5V, the drop-out voltage is
nothing but the input to output differential, since the minimum input voltage is 2.5V.
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TYPICAL PERFORMANCE CHARACTERISTICS
Unless otherwise specified: TJ = 25°C, COUT = 10µF, CIN = 10µF, S/D pin is tied to VIN, VOUT = 2.5V, VIN = VO(NOM) + 1V, IL =
10 mA.
Ground Current vs Output Load Current
Dropout Voltage vs Output Load Current
600
VOUT = 5V
4.9
4.85
4.8
500
400
4.75
4.7
125oC
4.65
4.6
25oC
300
200
100
4.55
4.5
-40oC
4.45
4.4
0
0
1
2
3
0
0.5
1
1.5
2
2.5
3
LOAD CURRENT (A)
OUTPUT LOAD CURRENT (A)
Figure 3.
Figure 4.
Ground Current vs Output Voltage
IL=3A
Shutdown IQ vs Junction Temperature
6
5
4
3
2
1
0
10
1
0.1
0.01
0.001
-40 -20
0
20 40 60 80 100 125
TEMPERATURE (oC)
1.8
2.3
2.8
3.3
3.8
4.3
4.8
OUTPUT VOLTAGE (V)
Figure 5.
Figure 6.
DC Load Reg. vs Junction Temperature
3
DC Line Regulation vs Temperature
3
2.5
2
2.5
2
1.5
1
1.5
1
0.5
0
0.5
0
-40 -20
0
20 40 60 80 100 125
-40 -20
0
20 40 60 80 100 125
JUNCTION TEMPERATURE (oC)
JUNCTION TEMPERATURE (oC)
Figure 7.
Figure 8.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Unless otherwise specified: TJ = 25°C, COUT = 10µF, CIN = 10µF, S/D pin is tied to VIN, VOUT = 2.5V, VIN = VO(NOM) + 1V, IL =
10 mA.
VIN vs VOUT Over Temperature
Noise vs Frequency
3.0
2.5
2.0
1.5
1.0
0.5
0.0
3.000
2.500
2.000
1.500
1.000
0.500
0.000
IL = 100mA
CIN = COUT = 10mF
-40oC
25oC
125oC
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
VIN (V)
100
1k
10k
100k
FREQUENCY (Hz)
Figure 9.
Figure 10.
Load Transient Response
CIN = COUT = 10µF, OSCON
Load Transient Response
CIN = COUT = 100µF, OSCON
VOUT
100mV/DIV
VOUT
100mV/DIV
ILOAD
3A/DIV
ILOAD
3A/DIV
TIME (50ms/DIV)
TIME (50ms/DIV)
Figure 11.
Figure 12.
Load Transient Response
CIN = COUT = 100µF, POSCAP
Load Transient Response
CIN = COUT = 10µF, TANTALUM
VOUT
100mV/DIV
VOUT
100mV/DIV
ILOAD
3A/DIV
ILOAD
3A/DIV
TIME (50ms/DIV)
TIME (50ms/DIV)
Figure 13.
Figure 14.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Unless otherwise specified: TJ = 25°C, COUT = 10µF, CIN = 10µF, S/D pin is tied to VIN, VOUT = 2.5V, VIN = VO(NOM) + 1V, IL =
10 mA.
Load Transient Response
CIN = COUT = 100µF, TANTALUM
Load Transient Response
CIN = COUT = 10µF, OSCON
VOUT
100mV/DIV
VOUT
100mV/DIV
ILOAD
3A/DIV
ILOAD
1A/DIV
TIME (50ms/DIV)
TIME (50ms/DIV)
Figure 15.
Figure 16.
Load Transient Response
CIN = COUT = 100µF, OSCON
Load Transient Response
CIN = COUT = 100µF, POSCAP
VOUT
100mV/DIV
VOUT
100mV/DIV
ILOAD
1A/DIV
ILOAD
1A/DIV
TIME (50ms/DIV)
TIME (50ms/DIV)
Figure 17.
Figure 18.
Load Transient Response
CIN = COUT = 10µF, TANTALUM
Load Transient Response
CIN = COUT = 10µF, TANTALUM
VOUT
100mV/DIV
VOUT
100mV/DIV
ILOAD
1A/DIV
ILOAD
1A/DIV
TIME (50ms/DIV)
TIME (50ms/DIV)
Figure 19.
Figure 20.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Unless otherwise specified: TJ = 25°C, COUT = 10µF, CIN = 10µF, S/D pin is tied to VIN, VOUT = 2.5V, VIN = VO(NOM) + 1V, IL =
10 mA.
Load Transient Response
CIN = 4 x 10µF CERAMIC
COUT = 3 x 10µF CERAMIC
Load Transient Response
CIN = 4 x 10µF CERAMIC
COUT = 3 x 10µF CERAMIC
V
V
OUT
OUT
100 mV/DIV
100 mV/DIV
V
OUT
= 2.5V
V
OUT
= 2.5V
T
1
1
T
I
I
OUT
OUT
1A/DIV
1A/DIV
T
T
2
2
TIME (5 ms/DIV)
TIME (1 ms/DIV)
Figure 21.
Figure 22.
Load Transient Response
CIN = 2 x 10µF CERAMIC
COUT = 2 x 10µF CERAMIC
Load Transient Response
CIN = 2 x 10µF CERAMIC
COUT = 2 x 10µF CERAMIC
V
OUT
V
OUT
@ 2.5V
100 mV/DIV
1
V
= 2.5V
OUT
T
T
1
I
OUT
I
I
OUT
@ 1A
OUT
@ 1A
1A/DIV
2
T
T
2
TIME (2 ms/DIV)
TIME (1 ms/DIV)
Figure 23.
Figure 24.
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Application Hints
SETTING THE OUTPUT VOLTAGE
The output voltage is set using the resistors R1 and R2 (see Typical Application Circuit). The output is also
dependent on the reference voltage (typically 1.216V) which is measured at the ADJ pin. The output voltage is
given by the equation:
VOUT = VADJ x ( 1 + R1 / R2)
(1)
This equation does not include errors due to the bias current flowing in the ADJ pin which is typically about 10
nA. This error term is negligible for most applications. If R1 is > 100kΩ , a small error may be introduced by the
ADJ bias current.
The tolerance of the external resistors used contributes a significant error to the output voltage accuracy, with 1%
resistors typically adding a total error of approximately 1.4% to the output voltage (this error is in addition to the
tolerance of the reference voltage at VADJ).
TURN-ON CHARACTERISTICS FOR OUTPUT VOLTAGES PROGRAMMED TO 2.0V OR BELOW
As Vin increases during start-up, the regulator output will track the input until Vin reaches the minimum operating
voltage (typically about 2.2V). For output voltages programmed to 2.0V or below, the regulator output may
momentarily exceed its programmed output voltage during start up. Outputs programmed to voltages above 2.0V
are not affected by this behavior.
EXTERNAL CAPACITORS
Like any low-dropout regulator, external capacitors are required to assure stability. these capacitors must be
correctly selected for proper performance.
INPUT CAPACITOR: An input capacitor of at least 10µF is required. Ceramic or Tantalum may be used, and
capacitance may be increased without limit
OUTPUT CAPACITOR: An output capacitor is required for loop stability. It must be located less than 1 cm from
the device and connected directly to the output and ground pins using traces which have no other currents
flowing through them (see PCB Layout section).
The minimum amount of output capacitance that can be used for stable operation is 10µF. For general usage
across all load currents and operating conditions, the part was characterized using a 10µF Tantalum input
capacitor. The minimum and maximum stable ESR range for the output capacitor was then measured which kept
the device stable, assuming any output capacitor whose value is greater than 10µF (see Figure 25 below).
10
STABLE REGION
1.0
COUT > 10mF
0.1
.01
.001
3
0
1
2
LOAD CURRENT (A)
Figure 25. ESR Curve for COUT (with 10µF Tantalum Input Capacitor)
It should be noted that it is possible to operate the part with an output capacitor whose ESR is below these limits,
assuming that sufficient ceramic input capacitance is provided. This will allow stable operation using ceramic
output capacitors (see next section).
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OPERATION WITH CERAMIC OUTPUT CAPACITORS
LP385X voltage regulators can operate with ceramic output capacitors if the values of input and output
capacitors are selected appropriately. The total ceramic output capacitance must be equal to or less than a
specified maximum value in order for the regulator to remain stable over all operating conditions. This maximum
amount of ceramic output capacitance is dependent upon the amount of ceramic input capacitance used as well
as the load current of the application. This relationship is shown in Figure 26, which graphs the maximum stable
value of ceramic output capacitance as a function of ceramic input capacitance for load currents of 1A, 2A, and
3A. For example, if the maximum load current is 1A, a 10µF ceramic input capacitor will allow stable operation
for values of ceramic output capacitance from 10µF up to about 500µF.
100
3A
2A
1A
10
100
1000
10
MAX. ALLOWABLE CERAMIC
OUTPUT CAPACITANCE (mF)
Figure 26. Maximum Ceramic Output Capacitance vs Ceramic Input Capacitance
If the maximum load current is 2A and a 10µF ceramic input capacitor is used, the regulator will be stable with
ceramic output capacitor values from 10µF up to about 50µF. At 3A of load current, the ratio of input to output
capacitance required approaches 1:1, meaning that whatever amount of ceramic output capacitance is used
must also be provided at the input for stable operation. For load currents between 1A, 2A, and 3A, interpolation
may be used to approximate values on the graph. When calculating the total ceramic output capacitance present
in an application, it is necessary to include any ceramic bypass capacitors connected to the regulator output.
CFF (Feed Forward Capacitor)
The capacitor CFF is required to add phase lead and help improve loop compensation. The correct amount of
capacitance depends on the value selected for R1 (see Typical Application Circuit). The capacitor should be
selected such that the zero frequency as given by the equation shown below is approximately 45 kHz:
Fz = 45,000 = 1 / ( 2 x π x R1 x CFF
)
(2)
A good quality ceramic with X5R or X7R dielectric should be used for this capacitor.
SELECTING A CAPACITOR
It is important to note that capacitance tolerance and variation with temperature must be taken into consideration
when selecting a capacitor so that the minimum required amount of capacitance is provided over the full
operating temperature range. In general, a good Tantalum capacitor will show very little capacitance variation
with temperature, but a ceramic may not be as good (depending on dielectric type). Aluminum electrolytics also
typically have large temperature variation of capacitance value.
Equally important to consider is a capacitor's ESR change with temperature: this is not an issue with ceramics,
as their ESR is extremely low. However, it is very important in Tantalum and aluminum electrolytic capacitors.
Both show increasing ESR at colder temperatures, but the increase in aluminum electrolytic capacitors is so
severe they may not be feasible for some applications (see Capacitor Characteristics Section).
CAPACITOR CHARACTERISTICS
CERAMIC: For values of capacitance in the 10 to 100 µF range, ceramics are usually larger and more costly
than tantalums but give superior AC performance for bypassing high frequency noise because of very low ESR
(typically less than 10 mΩ). However, some dielectric types do not have good capacitance characteristics as a
function of voltage and temperature.
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Z5U and Y5V dielectric ceramics have capacitance that drops severely with applied voltage. A typical Z5U or
Y5V capacitor can lose 60% of its rated capacitance with half of the rated voltage applied to it. The Z5U and Y5V
also exhibit a severe temperature effect, losing more than 50% of nominal capacitance at high and low limits of
the temperature range.
X7R and X5R dielectric ceramic capacitors are strongly recommended if ceramics are used, as they typically
maintain a capacitance range within ±20% of nominal over full operating ratings of temperature and voltage. Of
course, they are typically larger and more costly than Z5U/Y5U types for a given voltage and capacitance.
TANTALUM: Solid Tantalum capacitors are typically recommended for use on the output because their ESR is
very close to the ideal value required for loop compensation.
Tantalums also have good temperature stability: a good quality Tantalum will typically show a capacitance value
that varies less than 10-15% across the full temperature range of 125°C to −40°C. ESR will vary only about 2X
going from the high to low temperature limits.
The increasing ESR at lower temperatures can cause oscillations when marginal quality capacitors are used (if
the ESR of the capacitor is near the upper limit of the stability range at room temperature).
ALUMINUM: This capacitor type offers the most capacitance for the money. The disadvantages are that they are
larger in physical size, not widely available in surface mount, and have poor AC performance (especially at
higher frequencies) due to higher ESR and ESL.
Compared by size, the ESR of an aluminum electrolytic is higher than either Tantalum or ceramic, and it also
varies greatly with temperature. A typical aluminum electrolytic can exhibit an ESR increase of as much as 50X
when going from 25°C down to −40°C.
It should also be noted that many aluminum electrolytics only specify impedance at a frequency of 120 Hz, which
indicates they have poor high frequency performance. Only aluminum electrolytics that have an impedance
specified at a higher frequency (between 20 kHz and 100 kHz) should be used for the LP385X. Derating must be
applied to the manufacturer's ESR specification, since it is typically only valid at room temperature.
Any applications using aluminum electrolytics should be thoroughly tested at the lowest ambient operating
temperature where ESR is maximum.
PCB LAYOUT
Good PC layout practices must be used or instability can be induced because of ground loops and voltage drops.
The input and output capacitors must be directly connected to the input, output, and ground pins of the LP3856-
ADJ using traces which do not have other currents flowing in them (Kelvin connect).
The best way to do this is to lay out CIN and COUT near the device with short traces to the VIN, VOUT, and ground
pins. The regulator ground pin should be connected to the external circuit ground so that the regulator and its
capacitors have a "single point ground".
It should be noted that stability problems have been seen in applications where "vias" to an internal ground plane
were used at the ground points of the IC and the input and output capacitors. This was caused by varying ground
potentials at these nodes resulting from current flowing through the ground plane. Using a single point ground
technique for the regulator and it's capacitors fixed the problem.
Since high current flows through the traces going into VIN and coming from VOUT, Kelvin connect the capacitor
leads to these pins so there is no voltage drop in series with the input and output capacitors.
RFI/EMI SUSCEPTIBILITY
RFI (radio frequency interference) and EMI (electromagnetic interference) can degrade any integrated circuit's
performance because of the small dimensions of the geometries inside the device. In applications where circuit
sources are present which generate signals with significant high frequency energy content (> 1 MHz), care must
be taken to ensure that this does not affect the IC regulator.
If RFI/EMI noise is present on the input side of the regulator (such as applications where the input source comes
from the output of a switching regulator), good ceramic bypass capacitors must be used at the input pin of the IC.
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If a load is connected to the IC output which switches at high speed (such as a clock), the high-frequency current
pulses required by the load must be supplied by the capacitors on the IC output. Since the bandwidth of the
regulator loop is less than 100 kHz, the control circuitry cannot respond to load changes above that frequency.
The means the effective output impedance of the IC at frequencies above 100 kHz is determined only by the
output capacitor(s).
In applications where the load is switching at high speed, the output of the IC may need RF isolation from the
load. It is recommended that some inductance be placed between the output capacitor and the load, and good
RF bypass capacitors be placed directly across the load.
PCB layout is also critical in high noise environments, since RFI/EMI is easily radiated directly into PC traces.
Noisy circuitry should be isolated from "clean" circuits where possible, and grounded through a separate path. At
MHz frequencies, ground planes begin to look inductive and RFI/EMI can cause ground bounce across the
ground plane.
In multi-layer PCB applications, care should be taken in layout so that noisy power and ground planes do not
radiate directly into adjacent layers which carry analog power and ground.
OUTPUT NOISE
Noise is specified in two ways:
Spot Noise or Output noise density is the RMS sum of all noise sources, measured at the regulator output, at
a specific frequency (measured with a 1Hz bandwidth). This type of noise is usually plotted on a curve as a
function of frequency.
Total output Noise or Broad-band noise is the RMS sum of spot noise over a specified bandwidth, usually
several decades of frequencies.
Attention should be paid to the units of measurement. Spot noise is measured in units µV/√Hz or nV/√Hz and
total output noise is measured in µV(rms).
The primary source of noise in low-dropout regulators is the internal reference. In CMOS regulators, noise has a
low frequency component and a high frequency component, which depend strongly on the silicon area and
quiescent current. Noise can be reduced in two ways: by increasing the transistor area or by increasing the
current drawn by the internal reference. Increasing the area will decrease the chance of fitting the die into a
smaller package. Increasing the current drawn by the internal reference increases the total supply current
(ground pin current). Using an optimized trade-off of ground pin current and die size, LP3856-ADJ achieves low
noise performance and low quiescent current operation.
The total output noise specification for LP3856-ADJ is presented in the Electrical Characteristics table. The
Output noise density at different frequencies is represented by a curve under typical performance characteristics.
SHORT-CIRCUIT PROTECTION
The LP3856-ADJ is short circuit protected and in the event of a peak over-current condition, the short-circuit
control loop will rapidly drive the output PMOS pass element off. Once the power pass element shuts down, the
control loop will rapidly cycle the output on and off until the average power dissipation causes the thermal
shutdown circuit to respond to servo the on/off cycling to a lower frequency. Please refer to the section on
thermal information for power dissipation calculations.
SHUTDOWN OPERATION
A CMOS Logic low level signal at the Shutdown ( SD) pin will turn-off the regulator. Pin SD must be actively
terminated through a 10kΩ pull-up resistor for a proper operation. If this pin is driven from a source that actively
pulls high and low (such as a CMOS rail to rail comparator), the pull-up resistor is not required. This pin must be
tied to Vin if not used.
The Shutdown ( SD) pin threshold has no voltage hysteresis. If the Shutdown pin is actively driven, the voltage
transition must rise and fall cleanly and promptly.
12
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LP3856-ADJ
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SNVS243E –SEPTEMBER 2003–REVISED APRIL 2013
DROPOUT VOLTAGE
The dropout voltage of a regulator is defined as the minimum input-to-output differential required to stay within
2% of the nominal output voltage. For CMOS LDOs, the dropout voltage is the product of the load current and
the Rds(on) of the internal MOSFET.
REVERSE CURRENT PATH
The internal MOSFET in LP3856-ADJ has an inherent parasitic diode. During normal operation, the input voltage
is higher than the output voltage and the parasitic diode is reverse biased. However, if the output is pulled above
the input in an application, then current flows from the output to the input as the parasitic diode gets forward
biased. The output can be pulled above the input as long as the current in the parasitic diode is limited to 200mA
continuous and 1A peak.
POWER DISSIPATION/HEATSINKING
The LP3856-ADJ can deliver a continuous current of 3A over the full operating temperature range. A heatsink
may be required depending on the maximum power dissipation and maximum ambient temperature of the
application. Under all possible conditions, the junction temperature must be within the range specified under
operating conditions. The total power dissipation of the device is given by:
PD = (VIN−VOUT)IOUT+ (VIN)IGND
(3)
where IGND is the operating ground current of the device (specified under Electrical Characteristics).
The maximum allowable temperature rise (TRmax) depends on the maximum ambient temperature (TAmax) of the
application, and the maximum allowable junction temperature (TJmax):
TRmax = TJmax− TAmax
(4)
The maximum allowable value for junction to ambient Thermal Resistance, θJA, can be calculated using the
formula:
θJA = TRmax / PD
(5)
LP3856-ADJ is available in TO-220 and DDPAK/TO-263 packages. The thermal resistance depends on amount
of copper area or heat sink, and on air flow. If the maximum allowable value of θJA calculated above is ≥ 60 °C/W
for TO-220 package and ≥ 60 °C/W for DDPAK/TO-263 package no heatsink is needed since the package can
dissipate enough heat to satisfy these requirements. If the value for allowable θJA falls below these limits, a heat
sink is required.
HEATSINKING TO-220 PACKAGE
The thermal resistance of a TO-220 package can be reduced by attaching it to a heat sink or a copper plane on
a PC board. If a copper plane is to be used, the values of θJA will be same as shown in next section for
DDPAK/TO-263 package.
The heatsink to be used in the application should have a heatsink to ambient thermal resistance,
θHA≤ θJA − θCH − θJC
.
(6)
In this equation, θCH is the thermal resistance from the case to the surface of the heat sink and θJC is the thermal
resistance from the junction to the surface of the case. θJC is about 3°C/W for a TO-220 package. The value for
θCH depends on method of attachment, insulator, etc. θCH varies between 1.5°C/W to 2.5°C/W. If the exact value
is unknown, 2°C/W can be assumed.
HEATSINKING DDPAK/TO-263 PACKAGE
The DDPAK/TO-263 package uses the copper plane on the PCB as a heatsink. The tab of these packages are
soldered to the copper plane for heat sinking. Figure 27 shows a curve for the θJA of DDPAK/TO-263 package for
different copper area sizes, using a typical PCB with 1 ounce copper and no solder mask over the copper area
for heat sinking.
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Figure 27. θJA vs Copper (1 Ounce) Area for DDPAK/TO-263 Package
As shown in the figure, increasing the copper area beyond 1 square inch produces very little improvement. The
minimum value for θJA for the DDPAK/TO-263 package mounted to a PCB is 32°C/W.
Figure 28 shows the maximum allowable power dissipation for DDPAK/TO-263 packages for different ambient
temperatures, assuming θJA is 35°C/W and the maximum junction temperature is 125°C.
Figure 28. Maximum Power Dissipation vs Ambient Temperature for DDPAK/TO-263 Package
14
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LP3856-ADJ
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SNVS243E –SEPTEMBER 2003–REVISED APRIL 2013
REVISION HISTORY
Changes from Revision D (April 2013) to Revision E
Page
•
Changed layout of National Data Sheet to TI format .......................................................................................................... 14
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PACKAGE OPTION ADDENDUM
www.ti.com
7-Oct-2013
PACKAGING INFORMATION
Orderable Device
LP3856ES-ADJ/NOPB
LP3856ESX-ADJ/NOPB
LP3856ET-ADJ/NOPB
Status Package Type Package Pins Package
Eco Plan Lead/Ball Finish
MSL Peak Temp
Op Temp (°C)
-40 to 125
Device Marking
Samples
Drawing
Qty
(1)
(2)
(3)
(4/5)
ACTIVE
DDPAK/
TO-263
KTT
5
5
5
45
Pb-Free (RoHS
Exempt)
CU SN
CU SN
CU SN
Level-3-245C-168 HR
Level-3-245C-168 HR
Level-1-NA-UNLIM
LP3856ES
-ADJ
ACTIVE
ACTIVE
DDPAK/
TO-263
KTT
500
45
Pb-Free (RoHS
Exempt)
-40 to 125
LP3856ES
-ADJ
TO-220
NDH
Green (RoHS
& no Sb/Br)
-40 to 125
LP3856ET
-ADJ
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
7-Oct-2013
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
23-Sep-2013
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
B0
K0
P1
W
Pin1
Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant
(mm) W1 (mm)
LP3856ESX-ADJ/NOPB DDPAK/
TO-263
KTT
5
500
330.0
24.4
10.75 14.85
5.0
16.0
24.0
Q2
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
23-Sep-2013
*All dimensions are nominal
Device
Package Type Package Drawing Pins
DDPAK/TO-263 KTT
SPQ
Length (mm) Width (mm) Height (mm)
367.0 367.0 45.0
LP3856ESX-ADJ/NOPB
5
500
Pack Materials-Page 2
MECHANICAL DATA
NDH0005D
www.ti.com
MECHANICAL DATA
KTT0005B
TS5B (Rev D)
BOTTOM SIDE OF PACKAGE
www.ti.com
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