LM34919BTLX/NOPB [TI]
Ultra-Small 40-V 600-mA Constant On-Time Buck Switching Regulator;
| 型号： | LM34919BTLX/NOPB |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | Ultra-Small 40-V 600-mA Constant On-Time Buck Switching Regulator |
| 文件： | 总27页 (文件大小：1278K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LM34919B
LM34919B-Q1
www.ti.com
SNVS623B –MAY 2010–REVISED JULY 2013
LM34919B Ultra-Small 40-V 600-mA Constant On-Time
Buck Switching Regulator
Check for Samples: LM34919B, LM34919B-Q1
1
FEATURES
TYPICAL APPLICATIONS
2
•
•
AEC-Q100 Grade 1 Qualified (-40°C to 125°C)
•
•
•
Automotive Safety and Infotainment
Maximum Switching Frequency: 2.6 MHz
(VIN=14V,Vo=3.3V)
High Efficiency Point-Of-Load (POL) Regulator
Non-Isolated Telecommunication Buck
Regulator
•
•
•
•
•
•
Input Voltage Range: 6V to 40V
Integrated N-Channel Buck Switch
Integrated Startup Regulator
No loop compensation Required
Ultra-Fast transient Response
•
Secondary High Voltage Post Regulator
DESCRIPTION
The LM34919B Step-Down Switching Regulator
features all of the functions needed to implement a
low cost, efficient, buck bias regulator capable of
supplying 0.6A to the load. This buck regulator
contains an N-Channel Buck Switch, and is available
in a 10-pin DSBGA package. The constant on-time
feedback regulation scheme requires no loop
compensation, results in fast load transient response,
and simplifies circuit implementation. The operating
frequency remains constant with line and load
variations due to the inverse relationship between the
input voltage and the on-time. The valley current limit
results in a smooth transition from constant voltage to
constant current mode when current limit is detected,
reducing the frequency and output voltage, without
the use of foldback. Additional features include: VCC
under-voltage lockout, thermal shutdown, gate drive
under-voltage lockout, and maximum duty cycle
limiter.
Operating frequency remains constant with
Load Current and Input Voltage
•
•
•
•
•
•
•
•
Maximum Duty Cycle Limited During Startup
Adjustable Output Voltage
Valley Current Limit At 0.64A
Precision Internal Reference
Low Bias Current
Highly Efficient Operation
Thermal Shutdown
10-Pin DSBGA Package
Basic Step-Down Regulator
6V - 40V
Input
VIN
VCC
C3
C1
LM34919B
R
ON
BST
SW
C4
L1
RON/SD
V
OUT
SHUTDOWN
D1
R1
R2
R3
SS
ISEN
FB
C2
C6
RTN
SGND
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 © 2010–2013, Texas Instruments Incorporated
LM34919B
LM34919B-Q1
SNVS623B –MAY 2010–REVISED JULY 2013
www.ti.com
Connection Diagram
SW
D3
C3
B3
A3
D2
D1
C1
B1
A1
BST
D1
C1
B1
A1
D2
D3
C3
B3
A3
VIN
ISEN
VCC
SS
SGND
A2
A2
FB
RON/SD
RTN
Figure 1. Bump Side
Figure 2. Top View
Pin Descriptions
Pin No.
Name
Description
On-time control and
shutdown
Application Information
A1
RON/SD
An external resistor from VIN to this pin sets the buck switch on-time.
Grounding this pin shuts down the regulator.
A2
A3
RTN
FB
Circuit Ground
Ground for all internal circuitry other than the current limit detection.
Feedback input from
the regulated output
Internally connected to the regulation and over-voltage comparators. The
regulation level is 2.5V.
B1
B3
SGND
SS
Sense Ground
Softstart
Re-circulating current flows into this pin to the current sense resistor.
An internal current source charges an external capacitor to 2.5V, providing the
softstart function.
C1
C3
ISEN
VCC
Current sense
The re-circulating current flows through the internal sense resistor, and out of
this pin to the free-wheeling diode. Current limit is nominally set at 0.64A.
Output from the startup Nominally regulated at 7.0V. An external voltage (7V-14V) can be applied to
regulator
this pin to reduce internal dissipation. An internal diode connects VCC to VIN.
D1
D2
VIN
SW
Input supply voltage
Switching Node
Nominal input range is 6.0V to 40V.
Internally connected to the buck switch source. Connect to the inductor, free-
wheeling diode, and bootstrap capacitor.
D3
BST
Boost pin for bootstrap Connect a 0.022 µF capacitor from SW to this pin. The capacitor is charged
capacitor from VCC via an internal diode during each off-time.
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
2
Submit Documentation Feedback
Copyright © 2010–2013, Texas Instruments Incorporated
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
www.ti.com
SNVS623B –MAY 2010–REVISED JULY 2013
Absolute Maximum Ratings(1)
VIN to RTN
44V
52V
BST to RTN
SW to RTN (Steady State)
ESD Rating, Human Body Model(2)
BST to VCC
-1.5V to 44V
2kV
44V
BST to SW
14V
VCC to RTN
14V
SGND to RTN
-0.3V to +0.3V
-0.3V to 4V
-0.3 to 7V
-65°C to +150°C
SS, RON/SD to RTN
FB to RTN
Storage Temperature Range
For soldering specs see:
Junction Temperature
150°C
(1) Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which
operation of the device is intended to be functional. For specifications and test conditions, see the Electrical Characteristics.
(2) The human body model is a 100 pF capacitor discharged through a 1.5kΩ resistor into each pin.
Operating Ratings(1)
VIN
6.0V to 40V
−40°C to + 125°C
Junction Temperature
(1) Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which
operation of the device is intended to be functional. For specifications and test conditions, see the Electrical Characteristics.
Copyright © 2010–2013, Texas Instruments Incorporated
Submit Documentation Feedback
3
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
SNVS623B –MAY 2010–REVISED JULY 2013
www.ti.com
Electrical Characteristics
Specifications with standard type are for TJ = 25°C only; limits in boldface type apply over the full Operating Junction
Temperature (TJ) range. Minimum and Maximum limits are specified through test, design, or statistical correlation. Typical
values represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless
(1)
otherwise stated the following conditions apply: VIN = 12V, RON = 20 kΩ. See
.
Symbol
Parameter
Conditions
Min
Typ
Max
7.4
Units
Startup Regulator, VCC
VCCReg
VCC regulated output
VIN = 12V
6.6
5.3
7
V
VIN =6V, ICC = 3 mA,
5.91
20
VIN-VCC dropout voltage
VCC Output Impedance
ICC = 0 mA, non-switching
VCC = UVLOVCC + 250 mV
mV
0 mA ≤ ICC ≤ 5 mA, VIN = 6V
0 mA ≤ ICC ≤ 5 mA, VIN = 8V
VCC = 0V
24
12
Ω
VCC current limit(2)
15
mA
V
UVLOVCC VCC under-voltage lockout threshold
measured at VCC
VCC increasing
5.25
5.1
150
5.25
5.1
3
VCC decreasing
5.25
V
UVLOVCC hysteresis, at VCC
mV
V
VCC under-voltage lock-out threshold
measured at VIN
VIN increasing, ICC = 3 mA
VIN decreasing, ICC = 3 mA
100 mV overdrive
5.6
5.4
V
UVLOVCC filter delay
µs
mA
µA
IQ
IIN operating current
IIN shutdown current
Non-switching, FB = 3V, SW = Open
RON/SD = 0V, SW = Open
0.78
215
1.0
ISD
330
Switch Characteristics
Rds(on)
UVLOGD
Buck Switch Rds(on)
ITEST = 200 mA
0.5
3.6
3.2
400
1.0
Ω
V
Gate Drive UVLO
VBST - VSW Increasing
VBST - VSW Decreasing
2.65
4.40
UVLOGD hysteresis
mV
Softstart Pin
VSS
Pull-up voltage
2.5
V
Internal current source
VSS = 1V
10.5
µA
Current Limit
ILIM
Threshold
Current out of ISEN
0.52
0.64
135
50
0.76
A
Resistance from ISEN to SGND
Response time
mΩ
ns
On Timer
tON - 1
On-time
VIN = 12V, RON = 20kΩ
VIN = 24V, RON = 20 kΩ
VIN = 6V, RON = 20 kΩ
Voltage at RON/SD rising
Voltage at RON/SD
127
0.4
170
110
335
0.74
40
213
1.2
ns
ns
ns
V
tON - 2
On-time
tON - 3
On-time
Shutdown threshold
Threshold hysteresis
mV
Off Timer
tOFF
Minimum Off-time
VIN = 6V, ICC = 3mA
VIN = 8V, ICC = 3mA
60
58
88
82
120
118
ns
Regulation and Over-Voltage Comparators (FB Pin)
VREF
FB regulation threshold
FB over-voltage threshold
FB bias current
SS pin = steady state
FB = 3V
2.440
2.5
2.9
1
2.550
V
V
nA
(1) Typical specifications represent the most likely parametric norm at 25°C operation.
(2) VCC provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading
4
Submit Documentation Feedback
Copyright © 2010–2013, Texas Instruments Incorporated
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
www.ti.com
SNVS623B –MAY 2010–REVISED JULY 2013
Electrical Characteristics (continued)
Specifications with standard type are for TJ = 25°C only; limits in boldface type apply over the full Operating Junction
Temperature (TJ) range. Minimum and Maximum limits are specified through test, design, or statistical correlation. Typical
values represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless
otherwise stated the following conditions apply: VIN = 12V, RON = 20 kΩ. See (1)
.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Thermal Shutdown
TSD
Thermal shutdown temperature
Thermal shutdown hysteresis
175
20
°C
°C
Thermal Resistance
θJA Junction to Ambient
0 LFPM Air Flow
61
°C/W
Copyright © 2010–2013, Texas Instruments Incorporated
Submit Documentation Feedback
5
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
SNVS623B –MAY 2010–REVISED JULY 2013
www.ti.com
Typical Performance Characteristics
Efficiency at 2.1 MHz, 3.3V
Efficiency at 250 kHz, 3.3V
Figure 3.
Figure 4.
Efficiency at 2.1 MHz, 5V
VCC vs. VIN
Figure 5.
Figure 6.
VCC vs. ICC
ICC vs. Externally Applied VCC
Figure 7.
Figure 8.
6
Submit Documentation Feedback
Copyright © 2010–2013, Texas Instruments Incorporated
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
www.ti.com
SNVS623B –MAY 2010–REVISED JULY 2013
Typical Performance Characteristics (continued)
ON-TIME vs. VIN and RON
Voltage at the RON/SD Pin
Figure 9.
Figure 10.
Operating Current into VIN
Shutdown Current into VIN
Figure 11.
Figure 12.
VCC UVLO at Vin vs. Temperature
Gate Drive UVLO vs. Temperature
Figure 13.
Figure 14.
Copyright © 2010–2013, Texas Instruments Incorporated
Submit Documentation Feedback
7
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
SNVS623B –MAY 2010–REVISED JULY 2013
www.ti.com
Typical Performance Characteristics (continued)
VCC Voltage vs. Temperature
VCC Output Impedance vs. Temperature
Figure 15.
Figure 16.
VCC Current Limit vs. Temperature
Reference Voltage vs. Temperature
Figure 17.
Figure 18.
Soft-Start Current vs. Temperature
On-Time vs. Temperature
Figure 19.
Figure 20.
8
Submit Documentation Feedback
Copyright © 2010–2013, Texas Instruments Incorporated
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
www.ti.com
SNVS623B –MAY 2010–REVISED JULY 2013
Typical Performance Characteristics (continued)
Minimum Off-Time vs. Temperature
Current Limit Threshold vs. Temperature
Figure 21.
Operating & Shutdown Current vs. Temperature
Figure 22.
RON Pin Shutdown Threshold vs. Temperature
Figure 23.
Figure 24.
Copyright © 2010–2013, Texas Instruments Incorporated
Submit Documentation Feedback
9
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
SNVS623B –MAY 2010–REVISED JULY 2013
www.ti.com
BLOCK DIAGRAM
7V SERIES
REGULATOR
6V to 40V
Input
VIN
LM34919B
VCC
VCC
UVLO
C5
C1
C3
0.8V
OFF
TIMER
START
R
ON
GND
ON
TIMER
START
R
ON
FINISH
FINISH
RON/SD
BST
C4
SD
2.5V
Gate Drive
UVLO
V
IN
m
A
10.5
SS
LOGIC
C6
LEVEL
SHIFT
L1
Driver
SW
VOUT
R3
FB
THERMAL
SHUTDOWN
REGULATION
COMPARATOR
D1
R1
R2
CURRENT LIMIT
COMPARATOR
+
OVER-VOLTAGE
COMPARATOR
ISEN
-
R
SENSE
100 mW
2.9V
C2
-
64 mV
RTN
+
SGND
GND
10
Submit Documentation Feedback
Copyright © 2010–2013, Texas Instruments Incorporated
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
www.ti.com
SNVS623B –MAY 2010–REVISED JULY 2013
VIN
7.0V
UVLO
VCC
SW Pin
Inductor
Current
2.5V
SS Pin
V
OUT
t1
t2
Figure 25. Startup Sequence
Copyright © 2010–2013, Texas Instruments Incorporated
Submit Documentation Feedback
11
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
SNVS623B –MAY 2010–REVISED JULY 2013
www.ti.com
FUNCTIONAL DESCRIPTION
The LM34919B Step Down Switching Regulator features all the functions needed to implement a low-cost,
efficient buck bias power converter capable of supplying at least 0.6A to the load. This high voltage regulator
contains an N-Channel buck switch, is easy to implement, and is available in a DSBGA package. The regulator’s
operation is based on a constant on-time control scheme, where the on-time is determined by VIN. This feature
allows the operating frequency to remain relatively constant with load and input voltage variations. The feedback
control requires no loop compensation resulting in very fast load transient response. The valley current limit
detection circuit, internally set at 0.64A, holds the buck switch off until the high current level subsides. This
scheme protects against excessively high current if the output is short-circuited when VIN is high.
The LM34919B can be applied in numerous applications to efficiently regulate down higher voltages. Additional
features include: Thermal shutdown, VCC under-voltage lockout, gate drive under-voltage lockout, and maximum
duty cycle limiter.
Control Circuit Overview
The LM34919B buck DC-DC regulator employs a control scheme based on a comparator and a one-shot on-
timer, with the output voltage feedback (FB) compared to an internal reference (2.5V). If the FB voltage is below
the reference the buck switch is turned on for a time period determined by the input voltage and a programming
resistor (RON). Following the on-time the switch remains off until the FB voltage falls below the reference but not
less than the minimum off-time. The buck switch then turns on for another on-time period. Typically, during start-
up, or when the load current increases suddenly, the off-times are at the minimum. Once regulation is
established, the off-times are longer.
When in regulation, the LM34919B operates in continuous conduction mode at heavy load currents and
discontinuous conduction mode at light load currents. In continuous conduction mode current always flows
through the inductor, never reaching zero during the off-time. In this mode the operating frequency remains
relatively constant with load and line variations. The minimum load current for continuous conduction mode is
one-half the inductor’s ripple current amplitude. The operating frequency is approximately:
VOUT x (VIN œ 1.5V)
0.565 x 10-10 x (RON + 1.4 kW) x VIN
FS =
(1)
The buck switch duty cycle is approximately equal to:
tON
VOUT
=
DC =
tON + tOFF
VIN
(2)
In discontinuous conduction mode current through the inductor ramps up from zero to a peak during the on-time,
then ramps back to zero before the end of the off-time. The next on-time period starts when the voltage at FB
falls below the reference - until then the inductor current remains zero, and the load current is supplied by the
output capacitor. In this mode the operating frequency is lower than in continuous conduction mode, and varies
with load current. Conversion efficiency is maintained at light loads since the switching losses decrease with the
reduction in load and frequency. The approximate discontinuous operating frequency can be calculated as
follows:
VOUT2 x L1 x 6.27 x 1020
FS =
2
RL x (RON
)
(3)
where RL = the load resistance.
The output voltage is set by two external resistors (R1, R2). The regulated output voltage is calculated as
follows:
VOUT = 2.5 x (R1 + R2) / R2
(4)
Output voltage regulation is based on ripple voltage at the feedback input, normally obtained from the output
voltage ripple through the feedback resistors. The LM34919B requires a minimum of 25 mV of ripple voltage at
the FB pin. In cases where the capacitor’s ESR is insufficient additional series resistance may be required (R3).
12
Submit Documentation Feedback
Copyright © 2010–2013, Texas Instruments Incorporated
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
www.ti.com
SNVS623B –MAY 2010–REVISED JULY 2013
Startup Regulator, VCC
The start-up regulator is integral to the LM34919B. The input pin (VIN) can be connected directly to line voltage
up to 40V, with transient capability to 44V. The VCC output regulates at 7.0V, and is current limited at 15 mA.
Upon power up, the regulator sources current into the external capacitor at VCC (C3). When the voltage on the
VCC pin reaches the under-voltage lockout threshold of 5.25V, the buck switch is enabled and the Softstart pin is
released to allow the Softstart capacitor (C6) to charge up.
The minimum input voltage is determined by the VCC UVLO falling threshold (≊5.1V). When VCC falls below the
falling threshold the VCC UVLO activates to shut off the output. If VCC is externally loaded, the minimum input
voltage increases.
To reduce power dissipation in the startup regulator, an auxiliary voltage can be diode connected to the VCC pin.
Setting the auxiliary voltage to between 7V and 14V shuts off the internal regulator, reducing internal power
dissipation. The sum of the auxiliary voltage and the input voltage (VCC + VIN) cannot exceed 52V. Internally, a
diode connects VCC to VIN (see Figure 26).
VCC
C3
BST
C4
L1
D2
LM34919B
SW
V
OUT
D1
R3
R1
R2
ISEN
SGND
FB
C2
Figure 26. Self Biased Configuration
Regulation Comparator
The feedback voltage at FB is compared to the voltage at the Softstart pin (2.5V). In normal operation (the output
voltage is regulated), an on-time period is initiated when the voltage at FB falls below 2.5V. The buck switch
stays on for the programmed on-time, causing the FB voltage to rise above 2.5V. After the on-time period, the
buck switch stays off until the FB voltage falls below 2.5V. Input bias current at the FB pin is less than 100 nA
over temperature.
Over-Voltage Comparator
The voltage at FB is compared to an internal 2.9V reference. If the voltage at FB rises above 2.9V the on-time
pulse is immediately terminated. This condition can occur if the input voltage or the output load changes
suddenly, or if the inductor (L1) saturates. The buck switch remains off until the voltage at FB falls below 2.5V.
ON-Time Timer, and Shutdown
The on-time is determined by the RON resistor and the input voltage (VIN), and is calculated from:
0.565 x 10-10x(RON + 1.4 kW)
tON
=
+ 55 ns
VIN - 1.5V
(5)
The inverse relationship with VIN results in a nearly constant frequency as VIN is varied. To set a specific
continuous conduction mode switching frequency (FS), the RON resistor is determined from the following:
Copyright © 2010–2013, Texas Instruments Incorporated
Submit Documentation Feedback
13
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
SNVS623B –MAY 2010–REVISED JULY 2013
www.ti.com
VOUT x (VIN - 1.5V)
FS x 0.565 x 10-10 x VIN
- 1.4 kW
RON
=
(6)
In high frequency applications the minimum value for tON is limited by the maximum duty cycle required for
regulation and the minimum off-time. The minimum off-time limits the maximum duty cycle achievable with a low
voltage at VIN. At high values of VIN, the minimum on-time is limited to ≊ 90 ns.
The LM34919B can be remotely shut down by taking the RON/SD pin low (see Figure 27). In this mode the SS
pin is internally grounded, the on-timer is disabled, and bias currents are reduced. Releasing the RON/SD pin
allows normal operation to resume. The voltage at the RON/SD pin is between 1.4V and 5.0V, depending on VIN
and the RON resistor.
VIN
Input
Voltage
LM34919B
R
ON
RON/SD
STOP
RUN
Figure 27. Shutdown Implementation
Current Limit
Current limit detection occurs during the off-time by monitoring the recirculating current through the free-wheeling
diode (D1). Referring to the Block Diagram, when the buck switch is turned off the inductor current flows through
the load, into SGND, through the sense resistor, out of ISEN and through D1. If that current exceeds 0.64A the
current limit comparator output switches to delay the start of the next on-time period. The next on-time starts
when the current out of ISEN is below 0.64A and the voltage at FB is below 2.5V. If the overload condition
persists causing the inductor current to exceed 0.64A during each on-time, that is detected at the beginning of
each off-time. The operating frequency is lower due to longer-than-normal off-times.
Figure 28 shows the inductor current waveform. During normal operation the load current is Io, the average of
the ripple waveform. When the load resistance decreases the current ratchets up until the lower peak reaches
0.64A. During the Current Limited portion of Figure 28, the current ramps down to 0.64A during each off-time,
initiating the next on-time (assuming the voltage at FB is <2.5V). During each on-time the current ramps up an
amount equal to:
ΔI = (VIN - VOUT) x tON / L1
(7)
During this time the LM34919B is in a constant current mode, with an average load current (IOCL) equal to 0.64A
+ ΔI/2.
Generally, in applications where the switching frequency is higher than ≊300 kHz and uses a small value
inductor, the higher dl/dt of the inductor's ripple current results in an effectively lower valley current limit threshold
due to the response time of the current limit detection circuit. However, since the small value inductor results in a
relatively high ripple current amplitude (ΔI in Figure 28), the load current (IOCL) at current limit is typically in
excess of 640 mA.
14
Submit Documentation Feedback
Copyright © 2010–2013, Texas Instruments Incorporated
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
www.ti.com
SNVS623B –MAY 2010–REVISED JULY 2013
I
PK
DI
I
OCL
0.64A
I
O
Load Current
Increases
Normal Operation
Current Limited
Figure 28. Inductor Current - Current Limit Operation
N-Channel Buck Switch and Driver
The LM34919B integrates an N-Channel buck switch and associated floating high voltage gate driver. The peak
current allowed through the buck switch is 1.5A, and the maximum allowed average current is 1A. The gate
driver circuit works in conjunction with an external bootstrap capacitor and an internal high voltage diode. A 0.022
µF capacitor (C4) connected between BST and SW provides the voltage to the driver during the on-time. During
each off-time, the SW pin is at approximately -1V, and C4 charges from VCC through the internal diode. The
minimum off-time forced by the LM34919B ensures a minimum time each cycle to recharge the bootstrap
capacitor.
Softstart
The softstart feature allows the converter to gradually reach a steady state operating point, thereby reducing
start-up stresses and current surges. Upon turn-on, after VCC reaches the under-voltage threshold, an internal
10.5 µA current source charges up the external capacitor at the SS pin to 2.5V. The ramping voltage at SS (and
the non-inverting input of the regulation comparator) ramps up the output voltage in a controlled manner.
An internal switch grounds the SS pin if VCC is below the under-voltage lockout threshold, or if the RON/SD pin is
grounded.
Thermal Shutdown
The LM34919B should be operated so the junction temperature does not exceed 125°C. If the junction
temperature increases, an internal Thermal Shutdown circuit, which activates (typically) at 175°C, takes the
controller to a low power reset state by disabling the buck switch. This feature helps prevent catastrophic failures
from accidental device overheating. When the junction temperature reduces below 155°C (typical hysteresis =
20°C) normal operation resumes.
Copyright © 2010–2013, Texas Instruments Incorporated
Submit Documentation Feedback
15
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
SNVS623B –MAY 2010–REVISED JULY 2013
www.ti.com
APPLICATIONS INFORMATION
External Components
The procedure for calculating the external components is illustrated with the following design example. Referring
to the Block Diagram, the circuit is to be configured for the following specifications:
- VOUT = 3.3V
- VIN = 6V to 24V
- Minimum load current = 200 mA
- Maximum load current = 600 mA
- Switching Frequency = 1.5 MHz
- Soft-start time = 5 ms
R1 and R2: These resistors set the output voltage. The ratio of the feedback resistors is calculated from:
R1/R2 = (VOUT/2.5V) - 1
(8)
For this example, R1/R2 = 0.32. R1 and R2 should be chosen from standard value resistors in the range of 1.0
kΩ - 10 kΩ which satisfy the above ratio. For this example, 2.49kΩ is chosen for R2 and 787Ω for R1.
RON: This resistor sets the on-time, and (by default) the switching frequency. The switching frequency must be
less than 1.53 MHz to ensure the minimum forced on-time does not interfere with the circuit's proper operation at
the maximum input voltage. The RON resistor is calculated from the following equation, using the minimum input
voltage.
VOUT x (VIN(min) - 1.5V)
FS x 0.565 x 10-10 x VIN(min)
-1.4 kW = 27.8 kW
RON
=
(9)
Check that this value resistor does not set an on-time less than 90 ns at maximum VIN.
A standard value 28 kΩ resistor is used, resulting in a nominal frequency of 1.49 MHz. The minimum on-time is
≊129 ns at Vin = 24V, and the maximum on-time is ≊424 ns at Vin = 6V. Alternately, RON can be determined
using Equation 5 if a specific on-time is required.
L1: The main parameter affected by the inductor is the inductor current ripple amplitude (IOR). The minimum load
current is used to determine the maximum allowable ripple in order to maintain continuous conduction mode,
where the lower peak does not reach 0 mA. This is not a requirement of the LM34919B, but serves as a
guideline for selecting L1. For this case the maximum ripple current is:
IOR(MAX) = 2 x IOUT(min) = 400 mA
(10)
If the minimum load current is zero, use 20% of IOUT(max) for IOUT(min) in Equation 10. The ripple calculated in
Equation 10 is then used in the following equation:
(VIN(max) œ VOUT) x tON(min
)
L1 =
= 6.67 mH
IOR(max)
(11)
A standard value 8.2 µH inductor is selected. The maximum ripple amplitude, which occurs at maximum VIN,
calculates to 325 mA p-p, and the peak current is 763 mA at maximum load current. Ensure the selected inductor
is rated for this peak current.
C2 and R3: Since the LM34919B requires a minimum of 25 mVpp ripple at the FB pin for proper operation, the
required ripple at VOUT is increased by R1 and R2. This necessary ripple is created by the inductor ripple current
flowing through R3, and to a lesser extent by C2 and its ESR. The minimum inductor ripple current is calculated
using Equation 11, rearranged to solve for IOR at minimum VIN.
(VIN(min) œ VOUT) x ton(max)
= 140 mA
IOR(min)
=
L1
(12)
The minimum value for R3 is equal to:
25 mV x (R1 + R2)
R3(min)
=
= 0.24W
R2 x IOR (min)
(13)
16
Submit Documentation Feedback
Copyright © 2010–2013, Texas Instruments Incorporated
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
www.ti.com
SNVS623B –MAY 2010–REVISED JULY 2013
A standard value 0.27Ω resistor is used for R3 to allow for tolerances. C2 should generally be no smaller than
3.3 µF, although that is dependent on the frequency and the desired output characteristics. C2 should be a low
ESR good quality ceramic capacitor. Experimentation is usually necessary to determine the minimum value for
C2, as the nature of the load may require a larger value. A load which creates significant transients requires a
larger value for C2 than a non-varying load.
C1 and C5: C1’s purpose is to supply most of the switch current during the on-time, and limit the voltage ripple
at VIN, on the assumption that the voltage source feeding VIN has an output impedance greater than zero.
At maximum load current, when the buck switch turns on, the current into VIN suddenly increases to the lower
peak of the inductor’s ripple current, ramps up to the upper peak, then drops to zero at turn-off. The average
current during the on-time is the load current. For a worst case calculation, C1 must supply this average load
current during the maximum on-time, without letting the voltage at VIN drop more than 0.5V. The minimum value
for C1 is calculated from:
IOUT (max) x tON
C1 =
= 0.5 mF
DV
(14)
where tON is the maximum on-time, and ΔV is the allowable ripple voltage (0.5V). C5’s purpose is to minimize
transients and ringing due to long lead inductance leading to the VIN pin. A low ESR, 0.1 µF ceramic chip
capacitor must be located close to the VIN and RTN pins.
C3: The capacitor at the VCC pin provides noise filtering and stability for the VCC regulator. C3 should be no
smaller than 0.1 µF, and should be a good quality, low ESR, ceramic capacitor. C3’s value, and the VCC current
limit, determine a portion of the turn-on-time (t1 in Figure 25).
C4: The recommended value for C4 is 0.022 µF. A high quality ceramic capacitor with low ESR is recommended
as C4 supplies a surge current to charge the buck switch gate at each turn-on. A low ESR also helps ensure a
complete recharge during each off-time.
C6: The capacitor at the SS pin determines the softstart time, i.e. the time for the output voltage, to reach its final
value (t2 in Figure 25). The capacitor value is determined from the following:
t2 x 10.5 mA
= 0.021 mF
C6 =
2.5V
(15)
D1: A Schottky diode is recommended. Ultra-fast recovery diodes are not recommended as the high speed
transitions at the SW pin may inadvertently affect the IC’s operation through external or internal EMI. The diode
should be rated for the maximum input voltage, the maximum load current, and the peak current which occurs
when the current limit and maximum ripple current are reached simultaneously. The diode’s average power
dissipation is calculated from:
PD1 = VF x IOUT x (1-D)
(16)
where VF is the diode’s forward voltage drop, and D is the on-time duty cycle.
Final Circuit
The final circuit is shown in Figure 29, and its performance is shown in Figure 30 and Figure 31. Current limit
measured approximately 780 mA at 6V, and 812 mA at 24V.
Copyright © 2010–2013, Texas Instruments Incorporated
Submit Documentation Feedback
17
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
SNVS623B –MAY 2010–REVISED JULY 2013
www.ti.com
6V - 24V
Input
VCC
C3
0.1 mF
VIN
C5
C1
0.1 mF
2.2 mF
LM34919B
L1
8.2 mH
C4
0.022 mF
BST
SW
R
ON
28 kW
V
OUT
3.3V
RON/SD
SS
D1
SHUTDOWN
R1
787W
R3
0.27W
ISEN
FB
C6
0.022 mF
C2
22 mF
R2
2.49 kW
SGND
RTN
Figure 29. Example Circuit
Figure 30. Efficiency (Circuit of Figure 29)
Low-Output Ripple Configurations
Figure 31. Frequency vs. VIN (Circuit of Figure 29)
For applications where lower ripple at VOUT is required, the following options can be used to reduce or nearly
eliminate the ripple.
a) Reduced ripple configuration: In Figure 32, Cff is added across R1 to AC-couple the ripple at VOUT directly
to the FB pin. This allows the ripple at VOUT to be reduced to a minimum of 25 mVpp by reducing R3, since the
ripple at VOUT is not attenuated by the feedback resistors. The minimum value for Cff is determined from:
tON (max) x 3
Cff =
(R1//R2)
(17)
where tON(max) is the maximum on-time, which occurs at VIN(min). The next larger standard value capacitor should
be used for Cff. R1 and R2 should each be towards the upper end of the 2 kΩ to 10 kΩ range.
18
Submit Documentation Feedback
Copyright © 2010–2013, Texas Instruments Incorporated
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
www.ti.com
SNVS623B –MAY 2010–REVISED JULY 2013
L1
SW
FB
V
OUT
Cff
LM34919B
R1
R3
R2
C2
Figure 32. Reduced Ripple Configuration
b) Minimum ripple configuration: The circuit of Figure 33 provides minimum ripple at VOUT, determined
primarily by C2’s characteristics and the inductor’s ripple current since R3 is removed. RA and CA are chosen to
generate a sawtooth waveform at their junction, and that voltage is AC-coupled to the FB pin via CB. To
determine the values for RA, CA and CB, use the following procedure:
Calculate VA = VOUT - (VSW x (1 - (VOUT/VIN(min))))
(18)
where VSW is the absolute value of the voltage at the SW pin during the off-time (typically 1V). VA is the DC
voltage at the RA/CA junction, and is used in the next equation.
(VIN(min) - VA) x tON
RA x CA =
DV
(19)
where tON is the maximum on-time (at minimum input voltage), and ΔV is the desired ripple amplitude at the
RA/CA junction, typically 50 mV. RA and CA are then chosen from standard value components to satisfy the
above product. Typically CA is 3000 pF to 5000 pF, and RA is 10 kΩ to 300 kΩ. CB is then chosen large
compared to CA, typically 0.1 µF. R1 and R2 should each be towards the upper end of the 2 kΩ to 10 kΩ range.
L1
SW
V
OUT
CA
C2
LM34919B
RA
CB
R1
R2
FB
Figure 33. Minimum Output Ripple Using Ripple Injection
c) Alternate minimum ripple configuration: The circuit in Figure 34 is the same as that in Figure 29, except
the output voltage is taken from the junction of R3 and C2. The ripple at VOUT is determined by the inductor’s
ripple current and C2’s characteristics. However, R3 slightly degrades the load regulation. This circuit may be
suitable if the load current is fairly constant.
Copyright © 2010–2013, Texas Instruments Incorporated
Submit Documentation Feedback
19
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
SNVS623B –MAY 2010–REVISED JULY 2013
www.ti.com
L1
SW
FB
LM34919B
R1
R2
R3
V
OUT
C2
Figure 34. Alternate Minimum Output Ripple Configuration
Minimum Load Current
The LM34919B requires a minimum load current of 1 mA. If the load current falls below that level, the bootstrap
capacitor (C4) may discharge during the long off-time, and the circuit will either shutdown, or cycle on and off at
a low frequency. If the load current is expected to drop below 1 mA in the application, R1 and R2 should be
chosen low enough in value so they provide the minimum required current at nominal VOUT
.
PC Board Layout
Refer to application note AN-1112 for PC board guidelines for the DSBGA package.
The LM34919B regulation, over-voltage, and current limit comparators are very fast, and respond to short
duration noise pulses. Layout considerations are therefore critical for optimum performance. The layout must be
as neat and compact as possible, and all of the components must be as close as possible to their associated
pins. The two major current loops have currents which switch very fast, and so the loops should be as small as
possible to minimize conducted and radiated EMI. The first loop is that formed by C1, through the VIN to SW
pins, L1, C2, and back to C1.The second current loop is formed by D1, L1, C2 and the SGND and ISEN pins.
The power dissipation within the LM34919B can be approximated by determining the total conversion loss (PIN
-
POUT), and then subtracting the power losses in the free-wheeling diode and the inductor. The power loss in the
diode is approximately:
PD1 = Iout x VF x (1-D)
(20)
where Iout is the load current, VF is the diode’s forward voltage drop, and D is the on-time duty cycle. The power
loss in the inductor is approximately:
PL1 = Iout2 x RL x 1.1
(21)
where RL is the inductor’s DC resistance, and the 1.1 factor is an approximation for the AC losses. If it is
expected that the internal dissipation of the LM34919B will produce excessive junction temperatures during
normal operation, good use of the PC board’s ground plane can help to dissipate heat. Additionally the use of
wide PC board traces, where possible, can help conduct heat away from the IC. Judicious positioning of the PC
board within the end product, along with the use of any available air flow (forced or natural convection) can help
reduce the junction temperatures.
20
Submit Documentation Feedback
Copyright © 2010–2013, Texas Instruments Incorporated
Product Folder Links: LM34919B LM34919B-Q1
LM34919B
LM34919B-Q1
www.ti.com
SNVS623B –MAY 2010–REVISED JULY 2013
REVISION HISTORY
Changes from Revision A (February 2013) to Revision B
Page
•
Changed layout of National Data Sheet to TI format .......................................................................................................... 20
Copyright © 2010–2013, Texas Instruments Incorporated
Submit Documentation Feedback
21
Product Folder Links: LM34919B LM34919B-Q1
PACKAGE OPTION ADDENDUM
www.ti.com
1-Jul-2013
PACKAGING INFORMATION
Orderable Device
LM34919BQTL/NOPB
LM34919BQTLX/NOPB
LM34919BTL/NOPB
LM34919BTLX/NOPB
Status Package Type Package Pins Package
Eco Plan Lead/Ball Finish
MSL Peak Temp
Op Temp (°C)
-40 to 125
-40 to 125
-40 to 125
-40 to 125
Device Marking
Samples
Drawing
Qty
(1)
(2)
(3)
(4/5)
ACTIVE
DSBGA
DSBGA
DSBGA
DSBGA
YPA
10
10
10
10
250
Green (RoHS
& no Sb/Br)
SNAGCU
SNAGCU
SNAGCU
SNAGCU
Level-1-260C-UNLIM
Level-1-260C-UNLIM
Level-1-260C-UNLIM
Level-1-260C-UNLIM
SZRB
SZRB
SZCB
SZCB
ACTIVE
ACTIVE
ACTIVE
YPA
YPA
YPA
3000
250
Green (RoHS
& no Sb/Br)
Green (RoHS
& no Sb/Br)
3000
Green (RoHS
& no Sb/Br)
(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
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
1-Jul-2013
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.
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.
OTHER QUALIFIED VERSIONS OF LM34919B, LM34919B-Q1 :
Catalog: LM34919B
•
Automotive: LM34919B-Q1
•
NOTE: Qualified Version Definitions:
Catalog - TI's standard catalog product
•
Automotive - Q100 devices qualified for high-reliability automotive applications targeting zero defects
•
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
1-Jul-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)
LM34919BQTL/NOPB
DSBGA
YPA
YPA
YPA
YPA
10
10
10
10
250
3000
250
178.0
178.0
178.0
178.0
8.4
8.4
8.4
8.4
1.89
1.89
1.89
1.89
2.2
2.2
2.2
2.2
0.69
0.69
0.69
0.69
4.0
4.0
4.0
4.0
8.0
8.0
8.0
8.0
Q1
Q1
Q1
Q1
LM34919BQTLX/NOPB DSBGA
LM34919BTL/NOPB
LM34919BTLX/NOPB
DSBGA
DSBGA
3000
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
1-Jul-2013
*All dimensions are nominal
Device
Package Type Package Drawing Pins
SPQ
Length (mm) Width (mm) Height (mm)
LM34919BQTL/NOPB
LM34919BQTLX/NOPB
LM34919BTL/NOPB
LM34919BTLX/NOPB
DSBGA
DSBGA
DSBGA
DSBGA
YPA
YPA
YPA
YPA
10
10
10
10
250
3000
250
210.0
210.0
210.0
210.0
185.0
185.0
185.0
185.0
35.0
35.0
35.0
35.0
3000
Pack Materials-Page 2
MECHANICAL DATA
YPA0010
0.600
±0.075
D
E
TLP10XXX (Rev D)
D: Max = 2.012 mm, Min =1.951 mm
E: Max = 1.779 mm, Min =1.718 mm
4215069/A
12/12
A. All linear dimensions are in millimeters. Dimensioning and tolerancing per ASME Y14.5M-1994.
B. This drawing is subject to change without notice.
NOTES:
www.ti.com
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other
changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest
issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and
complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale
supplied at the time of order acknowledgment.
TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms
and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary
to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily
performed.
TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and
applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information
published by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty or
endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the
third party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration
and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altered
documentation. Information of third parties may be subject to additional restrictions.
Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service
voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice.
TI is not responsible or liable for any such statements.
Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements
concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support
that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which
anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause
harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use
of any TI components in safety-critical applications.
In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to
help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and
requirements. Nonetheless, such components are subject to these terms.
No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties
have executed a special agreement specifically governing such use.
Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in
military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components
which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and
regulatory requirements in connection with such use.
TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use of
non-designated products, TI will not be responsible for any failure to meet ISO/TS16949.
Products
Applications
Audio
www.ti.com/audio
amplifier.ti.com
dataconverter.ti.com
www.dlp.com
Automotive and Transportation www.ti.com/automotive
Communications and Telecom www.ti.com/communications
Amplifiers
Data Converters
DLP® Products
DSP
Computers and Peripherals
Consumer Electronics
Energy and Lighting
Industrial
www.ti.com/computers
www.ti.com/consumer-apps
www.ti.com/energy
dsp.ti.com
Clocks and Timers
Interface
www.ti.com/clocks
interface.ti.com
logic.ti.com
www.ti.com/industrial
www.ti.com/medical
Medical
Logic
Security
www.ti.com/security
Power Mgmt
Microcontrollers
RFID
power.ti.com
Space, Avionics and Defense
Video and Imaging
www.ti.com/space-avionics-defense
www.ti.com/video
microcontroller.ti.com
www.ti-rfid.com
www.ti.com/omap
OMAP Applications Processors
Wireless Connectivity
TI E2E Community
e2e.ti.com
www.ti.com/wirelessconnectivity
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2015, Texas Instruments Incorporated
相关型号：
LM34919TL/NOPB
2x1.5mm, 8-40V Wide Vin, 600mA, Constant On-Time Non-Synchronous Buck Regulator 10-DSBGA -40 to 125
TI
LM34919TLX/NOPB
IC 0.76 A SWITCHING REGULATOR, 1600 kHz SWITCHING FREQ-MAX, PBGA10, ROHS COMPLIANT, MICRO, SMD-10, Switching Regulator or Controller
NSC
©2020 ICPDF网 联系我们和版权申明