LP2987IM-3.0 [NSC]
Micropower, 200 mA Ultra Low-Dropout Voltage Regulator with Programmable Power-On Reset Delay; Low Noise Version Available (LP2988); 微功耗， 200毫安超低压差稳压器，可编程上电复位延迟;低噪音版本可用（ LP2988 ）
| 型号： | LP2987IM-3.0 |
| 厂家： | 
National Semiconductor |
| 描述： | Micropower, 200 mA Ultra Low-Dropout Voltage Regulator with Programmable Power-On Reset Delay; Low Noise Version Available (LP2988) |
| 文件： | 总19页 (文件大小：516K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
March 1999
LP2987/LP2988
Micropower, 200 mA Ultra Low-Dropout Voltage
Regulator with Programmable Power-On Reset Delay;
Low Noise Version Available (LP2988)
General Description
The LP2987/8 are fixed-output 200 mA precision LDO volt-
age regulators with power-ON reset delay which can be
implemented using a single external capacitor.
Features
n Ultra low dropout voltage
n Power-ON reset delay requires only one component
n Bypass pin for reduced output noise (LP2988)
n Guaranteed continuous output current 200 mA
n Guaranteed peak output current 250 mA
n SO-8 and mini SO-8 surface mount packages
The LP2988 is specifically designed for noise-critical appli-
cations. A single external capacitor connected to the Bypass
pin reduces regulator output noise.
>
™
Using an optimized VIP (Vertically Integrated PNP) pro-
<
n
2 µA quiescent current when shutdown
cess, these regulators deliver superior performance:
n Low ground pin current at all loads
@
@
Dropout Voltage: 180 mV 200 mA load, and 1 mV 1 mA
load (typical).
n 0.5% output voltage accuracy (“A” grade)
n Wide supply voltage range (16V max)
n Overtemperature/overcurrent protection
n −40˚C to +125˚C junction temperature range
@
@
Ground Pin Current: 1 mA 200 mA load, and 200 µA
10 mA load (typical).
Sleep Mode: The LP2987/8 draws less than 2 µA quiescent
current when shutdown pin is held low.
Applications
Error Flag/Reset: The error flag goes low when the output
drops approximately 5% below nominal. This pin also pro-
vides a power-ON reset signal if a capacitor is connected to
the DELAY pin.
n Cellular Phone
n Palmtop/Laptop Computer
n Camcorder, Personal Stereo, Camera
Precision Output: Standard product versions of the LP2987
and LP2988 are available with output voltages of 5.0V, 3.8V,
3.3V, 3.2V, 3.0V, or 2.8V, with guaranteed accuracy of 0.5%
(“A” grade) and 1% (standard grade) at room temperature.
Block Diagrams
DS100017-1
DS100017-2
™
VIP is a trademark of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation
DS100017
www.national.com
Connection Diagram (LP2987)
Surface Mount Packages:
Mini SO-8 Package Type MM: See NS Package Drawing Number MUA08A
SO-8 Package Type M: See NS Package Drawing Number M08A
DS100017-3
Top View
For ordering information, refer to Table 1 in this document.
Ordering Information (LP2987)
TABLE 1. Package Marking and Ordering Information
Output Voltage
Grade
A
Order Information
LP2987AIMMX-5.0
LP2987AIMM-5.0
LP2987IMMX-5.0
LP2987IMM-5.0
LP2987AIMMX-3.8
LP2987AIMM-3.8
LP2987IMMX-3.8
LP2987IMM-3.8
LP2987AIMMX-3.3
LP2987AIMM-3.3
LP2987IMMX-3.3
LP2987IMM-3.3
LP2987AIMMX-3.2
LP2987AIMM-3.2
LP2987IMMX-3.2
LP2987IMM-3.2
LP2987AIMMX-3.0
LP2987AIMM-3.0
LP2987IMMX-3.0
LP2987IMM-3.0
LP2987AIMMX-2.8
LP2987AIMM-2.8
LP2987IMMX-2.8
LP2987IMM-2.8
LP2987AIMX-5.0
LP2987AIM-5.0
LP2987IMX-5.0
LP2987IM-5.0
Package Marking
L44A
Supplied as:
5
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
5
A
L44A
5
STD
STD
A
L44B
5
L44B
3.8
3.8
3.8
3.8
3.3
3.3
3.3
3.3
3.2
3.2
3.2
3.2
3.0
3.0
3.0
3.0
2.8
2.8
2.8
2.8
5
L96A
A
L96A
STD
STD
A
L96B
L96B
L43A
A
L43A
STD
STD
A
L43B
L43B
L66A
A
L66A
STD
STD
A
L66B
L66B
L42A
A
L42A
STD
STD
A
L42B
L42B
L89A
A
L89A
STD
STD
A
L89B
L89B
2987AIM5.0
2987AIM5.0
2987IM5.0
2987IM5.0
2987AIM3.8
2987AIM3.8
2987IM3.8
2987IM3.8
2987AIM3.3
2987AIM3.3
5
A
5
STD
STD
A
5
3.8
3.8
3.8
3.8
3.3
3.3
LP2987AIMX-3.8
LP2987AIM-3.8
LP2987IMX-3.8
LP2987IM-3.8
A
STD
STD
A
LP2987AIMX-3.3
LP2987AIM-3.3
A
www.national.com
2
Ordering Information (LP2987) (Continued)
TABLE 1. Package Marking and Ordering Information (Continued)
Output Voltage
Grade
STD
STD
A
Order Information
LP2987IMX-3.3
LP2987IM-3.3
Package Marking
2987IM3.3
Supplied as:
3.3
3.3
3.2
3.2
3.2
3.2
3.0
3.0
3.0
3.0
2.8
2.8
2.8
2.8
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5 Units on Tape and Reel
Shipped in Anti-Static Rails
2.5 Units on Tape and Reel
Shipped in Anti-Static Rails
2.5 Units on Tape and Reel
Shipped in Anti-Static Rails
2987IM3.3
LP2987AIMX-3.2
LP2987AIM-3.2
LP2987IMX-3.2
LP2987AIM-3.2
LP2987IMX-3.0
LP2987AIM-3.0
LP2987IMX-3.0
LP2987IM-3.0
2987AIM3.2
2987AIM3.2
2987IM3.2
A
STD
STD
A
2987IM3.2
2987AIM3.0
2987AIM3.0
2987IM3.0
A
STD
STD
A
2987IM3.0
LP2987AIMX-2.8
LP2987AIM-2.8
LP2987IMX-2.8
LP298AIM-2.8
2987AIM2.8
2987AIM2.8
2987IM2.8
A
STD
STD
298AIM2.8
3
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Connection Diagram (LP2988)
Surface Mount Packages:
Mini SO-8 Package Type MM: See NS Package Drawing Number MUA08A
SO-8 Package Type M: See NS Package Drawing Number M08A
DS100017-16
Top View
For ordering information, refer to Table 2 in this document.
Ordering Information (LP2988)
TABLE 2. Package Marking and Ordering Information
Output Voltage
Grade
A
Order Information
LP2988AIMMX-5.0
LP2988AIMM-5.0
LP2988IMMX-5.0
LP2988IMM-5.0
LP2988AIMMX-3.8
LP2988AIMM-3.8
LP2988IMMX-3.8
LP2988IMM-3.8
LP2988AIMMX-3.3
LP2988AIMM-3.3
LP2988IMMX-3.3
LP2988IMM-3.3
LP2988AIMMX-3.2
LP2988AIMM-3.2
LP2988IMMX-3.2
LP2988IMM-3.2
LP2988AIMMX-3.0
LP2988AIMM-3.0
LP2988IMMX-3.0
LP2988IMM-3.0
LP2988AIMMX-2.8
LP2988AIMM-2.8
LP2988IMMX-2.8
LP2988IMM-2.8
LP2988AIMX-5.0
LP2988AIM-5.0
LP2988IMX-5.0
LP2988IM-5.0
Package Marking
L51A
Supplied as:
5
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
3.5k Units on Tape and Reel
250 Units on Tape and Reel
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
5
A
L51A
5
STD
STD
A
L51B
5
L51B
3.8
3.8
3.8
3.8
3.3
3.3
3.3
3.3
3.2
3.2
3.2
3.2
3.0
3.0
3.0
3.0
2.8
2.8
2.8
2.8
5
L0AA
A
L0AA
STD
STD
A
L0AB
L0AB
L50A
A
L50A
STD
STD
A
L50B
L50B
L67A
A
L67A
STD
STD
A
L67B
L67B
L49A
A
L49A
STD
STD
A
L49B
L49B
L0IA
A
L0IA
STD
STD
A
L0IB
L0IB
2988AIM5.0
2988AIM5.0
2988IM5.0
2988IM5.0
2988AIM3.8
2988AIM3.8
2988IM3.8
2988IM3.8
2988AIM3.3
2988AIM3.3
5
A
5
STD
STD
A
5
3.8
3.8
3.8
3.8
3.3
3.3
LP2988AIMX-3.8
LP2988AIM-3.8
LP2988IMX-3.8
LP2988IM-3.8
A
STD
STD
A
LP2988AIMX-3.3
LP2988AIM-3.3
A
www.national.com
4
Ordering Information (LP2988) (Continued)
TABLE 2. Package Marking and Ordering Information (Continued)
Output Voltage
Grade
STD
STD
A
Order Information
LP2988IMX-3.3
LP2988IM-3.3
Package Marking
2988IM3.3
Supplied as:
3.3
3.3
3.2
3.2
3.2
3.2
3.0
3.0
3.0
3.0
2.8
2.8
2.8
2.8
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5k Units on Tape and Reel
Shipped in Anti-Static Rails
2.5 Units on Tape and Reel
Shipped in Anti-Static Rails
2.5 Units on Tape and Reel
Shipped in Anti-Static Rails
2.5 Units on Tape and Reel
Shipped in Anti-Static Rails
2988IM3.3
LP2988AIMX-3.2
LP2988AIM-3.2
LP2988IMX-3.2
LP2988IM-3.2
2988AIM3.2
2988AIM3.2
2988IM3.2
A
STD
STD
A
2988IM3.2
LP2988AIMX-3.0
LP2988AIM-3.0
LP2988IMX-3.0
LP2988IM-3.0
2988AIM3.0
2988AIM3.0
2988IM3.0
A
STD
STD
A
2988IM3.0
LP2988AIMX-2.8
LP2988AIM-2.8
LP2988IMX-2.8
LP2988IM-2.8
2988AIM2.8
2988AIM2.8
2988IM2.8
A
STD
STD
2988IM2.8
5
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Supply Voltage
(Operating)
2.1V to +16V
−0.3V to +16V
−0.3V to +6V
Shutdown Pin
Sense Pin
Output Voltage
Storage Temperature Range
−65˚C to +150˚C
(Survival) (Note 4)
−0.3V to +16V
Operating Junction
Temperature Range
I
OUT (Survival)
Short Circuit Protected
−40˚C to +125˚C
Input-Output Voltage
(Survival) (Note 5)
Lead Temperature
(Soldering, 5 seconds)
−0.3V to +16V
260˚C
2 kV
ESD Rating (Note 2)
Power Dissipation (Note 3)
Internally Limited
Input Supply Voltage
(Survival)
−0.3V to +16V
Electrical Characteristics
Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the full operating temperature range. Un-
less otherwise specified: VIN = VO(NOM) + 1V, IL = 1 mA, COUT = 4.7 µF, CIN = 2.2 µF, VS/D = 2V.
LM2987/8AI-X.X
LM2987/8I-X.X
(Note 6)
(Note 6)
Symbol
∆VO
Parameter
Conditions
Typical
Units
Min
−0.5
−0.8
−1.8
Max
0.5
Min
−1.0
−1.6
−2.8
Max
1.0
Output Voltage
Tolerance
<
<
0.1 mA IL 200 mA
0.8
1.6
%VNOM
%/V
1.8
2.8
Output Voltage Line
Regulation
VO(NOM) + 1V ≤ VIN
≤
0.014
0.014
0.007
16V
0.032
0.032
VIN–VO
Dropout Voltage
(Note 7)
IL = 100 µA
IL = 75 mA
IL = 200 mA
IL = 100 µA
IL = 75 mA
IL = 200 mA
2.0
3.5
2.0
3.5
1
120
170
230
350
120
150
800
1400
2.1
120
170
230
350
120
150
800
1400
2.1
90
mV
µA
180
100
500
1
IGND
Ground Pin Current
mA
µA
3.7
3.7
<
VS/D 0.3V
0.05
400
1.5
1.5
I
O(PK)
Peak Output Current
Short Circuit Current
VOUT ≥ VO(NOM) − 5%
250
250
mA
IO(MAX)
RL = 0 (Steady State)
(Note 10)
400
en
LP2987 Output Noise
Voltage (RMS)
BW = 300 Hz to
50 kHz, VOUT = 3.3V
COUT = 10 µF
100
µV(RMS)
LP2988 Output Noise
Voltage (RMS)
BW = 300 Hz to
50 kHz, VOUT = 3.3V
COUT = 10 µF
20
CBYPASS = .01 µF
Ripple Rejection
f = 1 kHz, COUT = 10 µF
65
20
dB
=
CBYP 0 (LP2988)
Output Voltage
Temperature Coefficient
(Note 9)
ppm/˚C
www.national.com
6
Electrical Characteristics (Continued)
Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the full operating temperature range. Un-
less otherwise specified: VIN = VO(NOM) + 1V, IL = 1 mA, COUT = 4.7 µF, CIN = 2.2 µF, VS/D = 2V.
LM2987/8AI-X.X
LM2987/8I-X.X
(Note 6)
(Note 6)
Symbol
IDELAY
Parameter
Conditions
Typical
Units
Min
1.6
1.4
Max
2.8
Min
1.6
1.4
Max
2.8
Delay Pin Current
Source
2.2
µA
3.0
3.0
SHUTDOWN INPUT
VS/D S/D Input Voltage
VH = O/P ON
1.4
0.55
0
1.6
1.6
V
(Note 8)
VL = O/P OFF
VS/D = 0
0.18
−1
0.18
−1
IS/D
S/D Input Current
µA
VS/D = 5V
5
15
15
ERROR COMPARATOR
IOH
Output “HIGH” Leakage
VOH = 16V
1
1
0.01
150
µA
2
2
VOL
Output “LOW” Voltage
VIN = VO(NOM) − 0.5V,
IO(COMP) = 300 µA
220
350
−3.5
−2.5
−4.9
−3.3
220
350
−3.5
−2.5
−4.9
−3.3
mV
VTHR
(MAX)
Upper Threshold
Voltage
−5.5
−7.7
−5.5
−7.7
−4.6
VTHR
(MIN)
Lower Threshold
Voltage
−8.9
−8.9
%VOUT
−6.6
2.0
−13.0
−13.0
HYST
Hysteresis
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating the de-
vice outside of its rated operating conditions.
Note 2: The ESD rating of the Bypass pin is 500V (LP2988 only.)
Note 3: The maximum allowable power dissipation is a function of the maximum junction temperature, T (MAX), the junction-to-ambient thermal resistance, θ
,
J−A
J
and the ambient temperature, T . The maximum allowable power dissipation at any ambient temperature is calculated using:
A
The value of θ
for the SO-8 (M) package is 160˚C/W, and the mini SO-8 (MM) package is 200˚C/W. Exceeding the maximum allowable power dissipation will cause
J−A
excessive die temperature, and the regulator will go into thermal shutdown.
Note 4: If used in a dual-supply system where the regulator load is returned to a negative supply, the LM2987/8 output must be diode-clamped to ground.
Note 5: The output PNP structure contains a diode between the V and V
IN
terminals that is normally reverse-biased. Forcing the output above the input will turn
OUT
on this diode and may induce a latch-up mode which can damage the part (see Application Hints).
Note 6: Limits are 100% production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control
(SQC) methods. The limits are used to calculate National’s Average Outgoing Quality Level (AOQL).
Note 7: Dropout voltage is defined as the input to output differential at which the output voltage drops 100 mV below the value measured with a 1V differential.
Note 8: To prevent mis-operation, the Shutdown input must be driven by a signal that swings above V and below V with a slew rate not less than 40 mV/µs (see
H
L
Application Hints).
Note 9: Temperature coefficient is defined as the maximum (worst-case) change divided by the total temperature range.
Note 10: See Typical Performance Characteristics curves.
7
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Typical Performance Characteristics Unless otherwise specified: TA = 25˚C, COUT = 4.7 µF,
CIN = 2.2 µF, S/D is tied to VIN, VIN = VO(NOM) + 1V, IL = 1 mA.
VOUT vs Temperature
Dropout Voltage vs Temperature
DS100017-17
DS100017-18
Dropout Voltage vs Load Current
Dropout Characteristics
DS100017-19
DS100017-20
Ground Pin Current vs
Temperature and Load
Ground Pin Current vs
Load Current
DS100017-21
DS100017-22
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8
Typical Performance Characteristics Unless otherwise specified: TA = 25˚C, COUT = 4.7 µF,
CIN = 2.2 µF, S/D is tied to VIN, VIN = VO(NOM) + 1V, IL = 1 mA. (Continued)
Input Current vs VIN
Input Current vs VIN
DS100017-24
DS100017-23
Load Transient Response
Load Transient Response
DS100017-25
DS100017-26
Line Transient Response
Line Transient Response
DS100017-27
DS100017-28
9
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Typical Performance Characteristics Unless otherwise specified: TA = 25˚C, COUT = 4.7 µF,
CIN = 2.2 µF, S/D is tied to VIN, VIN = VO(NOM) + 1V, IL = 1 mA. (Continued)
Turn-On Waveform
Turn-On Waveform
DS100017-30
DS100017-29
Short Circuit Current
Short Circuit Current
DS100017-31
DS100017-32
Short Circuit Current
vs Output Voltage
Instantaneous Short Circuit Current
vs Temperature
DS100017-34
DS100017-33
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10
Typical Performance Characteristics Unless otherwise specified: TA = 25˚C, COUT = 4.7 µF,
CIN = 2.2 µF, S/D is tied to VIN, VIN = VO(NOM) + 1V, IL = 1 mA. (Continued)
Shutdown Pin Current vs
DC Load Regulation
Shutdown Pin Voltage
DS100017-36
DS100017-35
Shutdown Voltage
vs Temperature
Input to Output Leakage
vs Temperature
DS100017-37
DS100017-38
Delay Pin Current vs VIN
Delay Pin Current vs
Delay Pin Voltage
DS100017-45
DS100017-48
11
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Typical Performance Characteristics Unless otherwise specified: TA = 25˚C, COUT = 4.7 µF,
CIN = 2.2 µF, S/D is tied to VIN, VIN = VO(NOM) + 1V, IL = 1 mA. (Continued)
Delay Sink Current
vs Temperature
Delay Sink Current vs Temperature
DS100017-47
DS100017-46
Output Impedance vs Frequency
Output Impedance vs Frequency
DS100017-40
DS100017-41
Ripple Rejection (LP2987)
Ripple Rejection (LP2988)
DS100017-42
DS100017-51
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12
Typical Performance Characteristics Unless otherwise specified: TA = 25˚C, COUT = 4.7 µF,
CIN = 2.2 µF, S/D is tied to VIN, VIN = VO(NOM) + 1V, IL = 1 mA. (Continued)
Output Noise Voltage (LP2988)
Output Noise Density (LP2987)
DS100017-44
DS100017-39
Output Noise Density (LP2988)
Output Noise Density (LP2988)
DS100017-52
DS100017-53
Turn-On Time (LP2988)
Turn-On Time (LP2988)
DS100017-54
DS100017-55
13
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Typical Performance Characteristics Unless otherwise specified: TA = 25˚C, COUT = 4.7 µF,
CIN = 2.2 µF, S/D is tied to VIN, VIN = VO(NOM) + 1V, IL = 1 mA. (Continued)
Turn-On Time (LP2988)
DS100017-56
Basic Application Circuits
DS100017-5
DS100017-6
*Capacitance value shown is minimum required to assure stability, but may be increased without limit. Larger output capacitor provides improved dynamic
response.
**Shutdown must be actively terminated (see Application Hints). Tie to INPUT (pin 4) if not used.
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14
quired amount of output capacitance is provided over the full
operating temperature range. A good Tantalum capacitor will
show very little variation with temperature, but a ceramic
may not be as good (see next section).
Application Hints
EXTERNAL CAPACITORS
As with any low-dropout regulator, external capacitors are
required to assure stability. These capacitors must be cor-
rectly selected for proper performance.
The output capacitor should be located not more than 0.5”
from the output pin and returned to a clean analog ground.
INPUT CAPACITOR: An input capacitor (≥ 2.2 µF) is re-
quired between the LP2987/8 input and ground (amount of
capacitance may be increased without limit).
CAPACITOR CHARACTERISTICS
TANTALUM: A solid tantalum capacitor is the best choice for
the output capacitor on the LM2987/8. Available from many
sources, their typical ESR is very close to the ideal value re-
quired on the output of many LDO regulators.
This capacitor must be located a distance of not more than
0.5” from the input pin and returned to a clean analog
ground. Any good quality ceramic or tantalum may be used
for this capacitor.
Tantalums also have good temperature stability: a 4.7 µF
was tested and showed only a 10% decline in capacitance
as the temperature was decreased from +125˚C to −40˚C.
The ESR increased only about 2:1 over the same range of
temperature.
OUTPUT CAPACITOR: The output capacitor must meet the
requirement for minimum amount of capacitance and also
have an appropriate E.S.R. (equivalent series resistance)
value.
However, it should be noted that the increasing ESR at lower
temperatures present in all tantalums can cause oscillations
when marginal quality capacitors are used (where the ESR
of the capacitor is near the upper limit of the stability range at
room temperature).
Curves are provided which show the allowable ESR range
as a function of load current for 3V and 5V outputs.
ESR Curves For 5V Output
CERAMIC: The ESR of ceramic capacitor can be low
enough to cause an LDO regulator to oscillate: a 2.2 µF ce-
ramic was measured and found to have an ESR of 15 mΩ.
If a ceramic capacitor is to be used on the LP2987/8 output,
a 1Ω resistor should be placed in series with the capacitor to
provide a minimum ESR for the regulator.
A disadvantage of ceramic capacitors is that their capaci-
tance varies a lot with temperature: Large ceramic capaci-
tors are typically manufactured with the Z5U temperature
characteristic, which results in the capacitance dropping by
50% as the temperature goes from 25˚C to 80˚C.
This means you have to buy a capacitor with twice the mini-
mum COUT to assure stable operation up to 80˚C.
ALUMINUM: The large physical size of aluminum electrolyt-
ics makes them unsuitable for most applications. Their ESR
characteristics are also not well suited to the requirements of
LDO regulators. The ESR of a typical aluminum electrolytic
is higher than a tantalum, and it also varies greatly with tem-
perature.
DS100017-7
ESR Curves For 3V Output
A typical aluminum electrolytic can exhibit an ESR increase
of 50X when going from 20˚C to −40˚C. Also, some alumi-
num electrolytics can not be used below −25˚C because the
electrolyte will freeze.
POWER-ON RESET DELAY
A power-on reset function can be easily implemented using
the LP2987/8 by adding a single external capacitor to the
Delay pin. The Error output provides the power-on reset sig-
nal when input power is applied to the regulator.
The reset signal stays low for a pre-set time period after
power is applied to the regulator, and then goes high (see
Timing Diagram below).
DS100017-8
IMPORTANT: The output capacitor must maintain its ESR in
the stable region over the full operating temperature range of
the application to assure stability.
The minimum required amount of output capacitance is
4.7 µF. Output capacitor size can be increased without limit.
It is important to remember that capacitor tolerance and
variation with temperature must be taken into consideration
when selecting an output capacitor so that the minimum re-
15
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Application Hints (Continued)
DS100017-9
Timing Diagram for Power-Up
The external capacitor cDLY sets the delay time (TDELAY).
The value of capacitor required for a given time delay may
be calculated using the formula:
CDLY = TDELAY/(5.59 X 105)
To simplify design, a plot is provided below which shows val-
ues of CDLY versus delay time.
DS100017-10
LP2987/8 Equivalent Circuit
The output of comparator U2 is the ERR/RESET flag. Since
it is an open-collector output, it requires the use of a pull-up
resistor (RP). The 1.23V reference is tied to the inverting in-
put of U2, which means that its output is controlled by the
voltage applied to the non-inverting input.
The output of U1 (also an open-collector) will force the non-
inverting input of U2 to go low whenever the LP2987/8 regu-
lated output drops about 5% below nominal.
U1’s inverting input is also held at 1.23V. The other input
samples the regulated output through a resistive divider (RA
and RB). When the regulated output is at nominal voltage,
the voltage at the divider tap point will be 1.23V. If this volt-
age drops about 60 mV below 1.23V, the output of U1 will go
low forcing the output of U2 low (which is the ERROR state).
DS100017-11
Power-ON reset delay occurs when a capacitor (shown as
Plot of CDLY vs TDELAY
C
DLY) is connected to the Delay pin. At turn-ON, this capaci-
tor is initially fully discharged (which means the voltage at
the Delay pin is 0V). The output of U1 keeps CDLY fully dis-
charged (by sinking the 2.2 µA from the current source) until
the regulator output voltage comes up to within about 5% of
nominal. At this point, U1’s output stops sinking current and
DETAILS OF ERR/RESET CIRCUIT OPERATION: (Refer
to LP2987/8 Equivalent Circuit).
the 2.2 µA starts charging up CDLY
.
When the voltage across CDLY reaches 1.23V, the output of
U2 will go high (note that D1 limits the maximum voltage to
about 2V).
SELECTING CDLY: The maximum recommended value for
this capacitor is 1 µF. The capacitor must not have exces-
sively high leakage current, since it is being charged from a
2.2 µA current source.
Aluminum electrolytics can not be used, but good-quality
tantalum, ceremic, mica, or film types will work.
SHUTDOWN INPUT OPERATION
The LP2987/8 is shut off by driving the Shutdown input low,
and turned on by pulling it high. If this feature is not to be
used, the Shutdown input should be tied to VIN to keep the
regulator output on at all times.
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16
Care must be taken to ensure that the capacitor selected for
bypass will not have significant leakage current over the op-
erating temperature range of the application.
Application Hints (Continued)
To assure proper operation, the signal source used to drive
the Shutdown input must be able to swing above and below
the specified turn-on/turn-off voltage thresholds listed as VH
and VL, respectively (see Electrical Characteristics).
A high quality ceramic capacitor which uses either NPO or
COG type dielectiric material will typically have very low
leakage. Small surface-mount polypropolene or polycarbon-
ate film capacitors also have extremely low leakage, but are
slightly larger in size than ceramics.
It is also important that the turn-on (and turn-off) voltage sig-
nals applied to the Shutdown input have a slew rate which is
not less than 40 mV/µs.
CAUTION: the regulator output state can not be guaranteed
if a slow-moving AC (or DC) signal is applied that is in the
range between VH and VL.
REVERSE INPUT-OUTPUT VOLTAGE
The PNP power transistor used as the pass element in the
LP2987/8 has an inherent diode connected between the
regulator output and input.
During normal operation (where the input voltage is higher
than the output) this diode is reverse-biased.
However, if the output is pulled above the input, this diode
will turn ON and current will flow into the regulator output.
In such cases, a parasitic SCR can latch which will allow a
high current to flow into VIN (and out the ground pin), which
can damage the part.
DS100017-49
In any application where the output may be pulled above the
input, an external Schottky diode must be connected from
V
IN to VOUT (cathode on VIN, anode on VOUT), to limit the re-
verse voltage across the LP2987/8 to 0.3V (see Absolute
Maximum Ratings).
BYPASS CAPACITOR (LP2988)
The capacitor connected to the Bypass pin must have very
low leakage. The current flowing out of the Bypass pin
comes from the Bandgap reference, which is used to set the
output voltage. Since the Bandgap circuit has only a few mi-
croamps flowing in it, loading effects due to leakage current
will cause a change in the regulated output voltage.
Curves are provided which show the effect of loading the By-
pass pin on the regulated output voltage.
DS100017-50
17
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Physical Dimensions inches (millimeters) unless otherwise noted
Mini SO-8 Package Type MM
NS Package Number MUA08A
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18
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
SO-8 Package Type M
NS Package Number M08A
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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL
SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com
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Response Group
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