LM2695 [TI]
LM2695 High Voltage (30V, 1.25A) Step Down Switching Regulator;
| 型号： | LM2695 |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | LM2695 High Voltage (30V, 1.25A) Step Down Switching Regulator |
| 文件： | 总21页 (文件大小：914K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LM2695
www.ti.com
SNVS413A –JANUARY 2006–REVISED APRIL 2013
LM2695 High Voltage (30V, 1.25A) Step Down Switching Regulator
Check for Samples: LM2695
1
FEATURES
DESCRIPTION
The LM2695 Step Down Switching Regulator features
all of the functions needed to implement a low cost,
efficient, buck bias regulator capable of supplying
1.25A to the load. This buck regulator contains a 33V
N-Channel Buck Switch, and is available in the
thermally enhanced WSON-10 and HTSSOP-14
packages. The hysteretic 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
current limit detection is set at 1.25A. Additional
features include: VCC under-voltage lockout, thermal
shutdown, gate drive under-voltage lockout, and
maximum duty cycle limiter.
2
•
•
•
•
•
•
Integrated 33V, N-Channel Buck Switch
Integrated Start-Up Regulator
Input Voltage Range: 8V to 30V
No Loop Compensation Required
Ultra-Fast Transient Response
Operating Frequency Remains Constant with
Load Current and Input Voltage
•
•
•
•
•
•
•
Maximum Duty Cycle Limited During Start-Up
Adjustable Output Voltage
Valley Current Limit At 1.25A
Precision Internal Reference
Low Bias Current
Highly Efficient Operation
Thermal Shutdown
PACKAGE
•
•
•
10-Pin WSON (4 mm x 4 mm)
14-Pin HTSSOP
TYPICAL APPLICATIONS
•
•
High Efficiency Point-Of-Load (POL) Regulator
Exposed Thermal Pad For Improved Heat
Dissipation
Non-Isolated Telecommunication Buck
Regulator
•
Secondary High Voltage Post Regulator
Basic Step Down Regulator
8V - 30V
Input
VIN
VCC
BST
SW
C3
C1
R
ON
LM2695
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 © 2006–2013, Texas Instruments Incorporated
LM2695
SNVS413A –JANUARY 2006–REVISED APRIL 2013
www.ti.com
Connection Diagram
14
1
2
3
4
5
6
7
10
9
1
2
3
4
5
NC
SW
NC
VIN
VCC
13
12
11
10
9
BST
SW
VIN
VCC
8
BST
RON/SD
ISEN
SGND
RTN
7
ISEN
RON/SD
SS
SS
FB
6
SGND
RTN
NC
FB
8
NC
Figure 1. 14-Lead HTSSOP (Top View)
See PWP0014A Package
Figure 2. 10-Lead WSON (Top View)
See DPR0010A Package
PIN DESCRIPTIONS
Pin Number
Name
Description
Switching Node
Application Information
WSON-10
HTSSOP-14
1
2
3
2
SW
Internally connected to the buck switch source.
Connect to the inductor, free-wheeling diode, and
bootstrap capacitor.
3
4
BST
ISEN
Boost pin for bootstrap capacitor
Current sense
Connect a 0.022 µF capacitor from SW to this pin.
The capacitor is charged from VCC via an internal
diode during each off-time.
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 1.25A.
4
5
6
7
5
6
SGND
RTN
FB
Sense Ground
Circuit Ground
Re-circulating current flows into this pin to the current
sense resistor.
Ground for all internal circuitry other than the current
limit detection.
9
Feedback input from the regulated
output
Internally connected to the regulation and over-
voltage comparators. The regulation level is 2.5V.
10
SS
Softstart
An internal 12.3 µA current source charges an
external capacitor to 2.5V, providing the softstart
function.
8
9
11
12
RON/SD
On-time control and shutdown
Output from the startup regulator
An external resistor from VIN to this pin sets the buck
switch on-time. Grounding this pin shuts down the
regulator.
VCC
Nominally regulates at 7.0V. An external voltage (8V-
14V) can be applied to this pin to reduce internal
dissipation. An internal diode connects VCC to VIN
Nominal input range is 8.0V to 30V.
No internal connection.
.
10
13
VIN
NC
EP
Input supply voltage
No connection.
Exposed Pad
1,7,8,14
Exposed metal pad on the underside of the device. It
is recommended to connect this pad to the PC board
ground plane to aid in heat dissipation.
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.
2
Submit Documentation Feedback
Copyright © 2006–2013, Texas Instruments Incorporated
Product Folder Links: LM2695
LM2695
www.ti.com
SNVS413A –JANUARY 2006–REVISED APRIL 2013
Absolute Maximum Ratings(1)(2)(3)
VIN to RTN
33V
47V
BST to RTN
SW to RTN (Steady State)
ESD Rating(4)
-1.5V
Human Body Model
2kV
BST to VCC
33V
VIN to SW
33V
BST to SW
14V
VCC to RTN
14V
SGND to RTN
-0.3V to +0.3V
See Text
-0.3V to 4V
-0.3 to 7V
-65°C to +150°C
150°C
Current out of ISEN
SS to RTN
All Other Inputs to RTN
Storage Temperature Range
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 ensured specifications and test conditions, see the Electrical Characteristics.
(2) For detailed information on soldering plastic WSON-10 packages, refer to the Packaging Data Book available from TI.
(3) If Military/Aerospace specified devices are required, please contact the TI Sales Office/Distributors for availability and specifications.
(4) The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin.
Operating Ratings(1)
VIN
8.0V to 30V
−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 ensured specifications and test conditions, see the Electrical Characteristics.
Copyright © 2006–2013, Texas Instruments Incorporated
Submit Documentation Feedback
3
Product Folder Links: LM2695
LM2695
SNVS413A –JANUARY 2006–REVISED APRIL 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 ensured 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 = 24V, RON = 200kΩ(1)
.
Symbol
Parameter
Conditions
Min
6.6
Typ
Max
7.4
Units
Start-Up Regulator, VCC
VCCReg
VCC regulated output
7
V
V
ICC = 0 mA,
VIN-VCC dropout voltage
1.3
VCC = UVLOVCC + 250 mV
0 mA ≤ ICC ≤ 5 mA
VCC = 0V
VCC output impedance
VCC current limit(2)
140
9.7
Ω
mA
V
UVLOVCC
VCC under-voltage lockout
threshold
VCC increasing
5.7
UVLOVCC hysteresis
UVLOVCC filter delay
IIN operating current
IIN shutdown current
VCC decreasing
150
3
mV
µs
100 mV overdrive
Non-switching, FB = 3V
RON/SD = 0V
0.5
95
0.8
mA
µA
200
Switch Characteristics
Rds(on)
UVLOGD
Buck Switch Rds(on)
ITEST = 200 mA
0.33
4.4
0.7
5.5
Ω
V
Gate Drive UVLO
VBST - VSW Increasing
3.0
UVLOGD hysteresis
480
mV
Softstart Pin
Pull-up voltage
2.5
V
Internal current source
12.3
µA
Current Limit
ILIM
Threshold
Current out of ISEN
1
1.25
130
150
1.5
A
Resistance from ISEN to SGND
Response time
mΩ
ns
On Timer
tON - 1
On-time
VIN = 10V, RON = 200 kΩ
VIN = 30V, RON = 200 kΩ
Voltage at RON/SD rising
Voltage at RON/SD falling
2.1
2.8
950
0.8
37
3.6
1.2
µs
ns
V
tON - 2
On-time
Shutdown threshold
Threshold hysteresis
0.45
mV
Off Timer
tOFF
Minimum Off-time
250
ns
Regulation and Over-Voltage Comparators (FB Pin)
VREF
FB regulation threshold
FB over-voltage threshold
FB bias current
SS pin = steady state
2.440
2.5
2.9
1
2.550
V
V
nA
Thermal Shutdown
TSD Thermal shutdown temperature
Thermal shutdown hysteresis
Thermal Resistance
175
20
°C
°C
θJA
Junction to Ambient
0 LFPM Air Flow
°C/W
°C/W
Both Packages
Both Packages
37
θJC
Junction to Case
6.6
(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 © 2006–2013, Texas Instruments Incorporated
Product Folder Links: LM2695
LM2695
www.ti.com
SNVS413A –JANUARY 2006–REVISED APRIL 2013
Typical Performance Characteristics
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0
7.5
7.0
6.5
6.0
5.5
5.0
R
= 400k
ON
F
= 150 kHz
S
F
= 45 kHz
S
R
= 200k
ON
F
= 750 kHz
S
R
= 100k
ON
R
= 44.2k
ON
0
10
20
30
6.5
7.0
7.5
8.0
(V)
8.5
9.0
V
(V)
IN
V
IN
Figure 3. VCC vs VIN
Figure 4. ON-Time vs VIN and RON
Typical Application Circuit and Block Diagram
7V SERIES
REGULATOR
8V-30V
Input
LM2695
VIN
VCC
C3
VCC
THERMAL
UVLO
SHUTDOWN
C5
C1
-
R
ON
+
250 ns
OFF TIMER
ON TIMER
RON
/SD
0.8V
RON
START
START
COMPLETE
COMPLETE
BST
GATE DRIVE
UVLO
C4
VIN
2.5V
12.3 mA
DRIVER
LOGIC
SS
L1
LEVEL
SHIFT
C6
DRIVER
SW
V
OUT1
+
-
FB
REGULATION
COMPARATOR
+
D1
CURRENT LIMIT
COMPARATOR
R3
-
OVER-
ISEN
R1
V
OUT2
VOLTAGE
2.9V
+
-
R
SENSE
50 mW
SGND
COMPARATOR
-
+
RTN
62.5 mV
C2
R2
Copyright © 2006–2013, Texas Instruments Incorporated
Submit Documentation Feedback
5
Product Folder Links: LM2695
LM2695
SNVS413A –JANUARY 2006–REVISED APRIL 2013
www.ti.com
Functional Description
The LM2695 Step Down Switching Regulator features all the functions needed to implement a low cost, efficient
buck bias power converter capable of supplying 1.25A to the load. This high voltage regulator contains a 33V N-
Channel buck switch, is easy to implement, and is available in the thermally enhanced WSON-10 and HTSSOP-
14 packages. The regulator’s operation is based on a hysteretic control scheme, and uses an on-time control
which varies inversely with VIN. This feature allows the operating frequency to remain relatively constant with
load and input voltage variations. The hysteretic control requires no loop compensation resulting in very fast load
transient response. The valley current limit detection circuit, internally set at 1.25A, holds the buck switch off until
the high current level subsides. The functional block diagram is shown in Typical Application Circuit and Block
Diagram.
The LM2695 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.
Hysteretic Control Circuit Overview
The LM2695 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 for a minimum of 250 ns, and until the FB voltage
falls below the reference. 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 of 250 ns. Once regulation is
established, the off-times are longer.
When in regulation, the LM2695 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
FS =
1.3 x 10-10 x RON
(1)
The buck switch duty cycle is equal to:
tON
VOUT
VIN
=
DC =
tON + tOFF
(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 (C2). 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 reduce with
the reduction in load and frequency. The approximate discontinuous operating frequency can be calculated as
follows:
VOUT2 x L1 x 1.18 x 1020
FS =
2
RL x (RON
)
where
•
RL = the load resistance
(3)
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)
6
Submit Documentation Feedback
Copyright © 2006–2013, Texas Instruments Incorporated
Product Folder Links: LM2695
LM2695
www.ti.com
SNVS413A –JANUARY 2006–REVISED APRIL 2013
Output voltage regulation is based on ripple voltage at the feedback input, requiring a minimum amount of ESR
for the output capacitor C2. The LM2695 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 in Typical Application
Circuit and Block Diagram).
For applications where lower output voltage ripple is required the output can be taken directly from a low ESR
output capacitor as shown in Figure 5. However, R3 slightly degrades the load regulation.
L1
SW
LM2695
R1
R2
R3
FB
V
OUT2
C2
Figure 5. Low Ripple Output Configuration
Copyright © 2006–2013, Texas Instruments Incorporated
Submit Documentation Feedback
7
Product Folder Links: LM2695
LM2695
SNVS413A –JANUARY 2006–REVISED APRIL 2013
www.ti.com
Start-Up Regulator, VCC
The start-up regulator is integral to the LM2695. The input pin (VIN) can be connected directly to line voltage up
to 30V, with transient capability to 33V. The VCC output regulates at 7.0V, and is current limited at 9.7 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 5.7V, 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 regulator’s dropout voltage, the VCC UVLO falling threshold
(≊5.5V), and the frequency. 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 since the output impedance at VCC is
≊140Ω.
To reduce power dissipation in the start-up regulator, an auxiliary voltage can be diode connected to the VCC pin.
Setting the auxiliary voltage to between 8V 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 47V. Internally, a
diode connects VCC to VIN. See Figure 6.
VCC
C3
BST
C4
L1
D2
LM2695
SW
V
OUT1
D1
R3
R1
R2
ISEN
SGND
FB
C2
Figure 6. 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 for the LM2695 is determined by the RON resistor and the input voltage (VIN), and is calculated from:
1.3 x 10-10 x RON
tON
=
VIN
(5)
8
Submit Documentation Feedback
Copyright © 2006–2013, Texas Instruments Incorporated
Product Folder Links: LM2695
LM2695
www.ti.com
SNVS413A –JANUARY 2006–REVISED APRIL 2013
See Figure 4. 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:
VOUT
RON
=
FS x 1.3 x 10-10
(6)
In high frequency applicatons the minimum value for tON is limited by the maximum duty cycle required for
regulation and the minimum off-time of (250 ns, ±15%). The minimum off-time limits the maximum duty cycle
achievable with a low voltage at VIN. The minimum allowed on-time to regulate the desired VOUT at the minimum
VIN is determined from the following:
VOUT x 288 ns
tON(min)
=
(VIN(min) - VOUT
)
(7)
The LM2695 can be remotely shut down by taking the RON/SD pin below 0.8V. See Figure 7. 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 1.5V and 3.0V, depending on VIN
and the RON resistor.
VIN
Input
Voltage
LM2695
R
ON
RON/SD
STOP
RUN
Figure 7. 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 Typical Application Circuit and 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 1.25A the current limit comparator output switches to delay the start of the next on-time
period if the voltage at FB is below 2.5V. The next on-time starts when the current out of ISEN is below 1.25A
and the voltage at FB is below 2.5V. If the overload condition persists causing the inductor current to exceed
1.25A 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 8 illustrates 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
1.25A. During the Current Limited portion of Figure 8, the current ramps down to 1.25A 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
(8)
During this time the LM2695 is in a constant current mode, with an average load current (IOCL) equal to 1.25A +
ΔI/2.
Copyright © 2006–2013, Texas Instruments Incorporated
Submit Documentation Feedback
9
Product Folder Links: LM2695
LM2695
SNVS413A –JANUARY 2006–REVISED APRIL 2013
www.ti.com
I
PK
DI
I
OCL
1.25A
I
O
Load Current
Increases
Normal Operation
Current Limited
Figure 8. Inductor Current - Current Limit Operation
The current limit threshold can be increased by connecting an external resistor between SGND and ISEN. The
external resistor will typically be less than 1Ω. The peak current out of SW and ISEN must not exceed 2A. The
average current out of SW must be less than 1.5A.
N - Channel Buck Switch and Driver
The LM2695 integrates an N-Channel buck switch and associated floating high voltage gate driver. The peak
current allowed through the buck switch is 2A, and the maximum allowed average current is 1.5A. 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 of 250 ns 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
12.3 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, if a thermal shutdown
occurs, or if the RON/SD pin is grounded.
Thermal Shutdown
The LM2695 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 and the on-timer, and grounding the Softstart pin. This feature
helps prevent catastrophic failures from accidental device overheating. When the junction temperature reduces
below 155°C (typical hysteresis = 20°C), the Softstart pin is released and normal operation resumes.
10
Submit Documentation Feedback
Copyright © 2006–2013, Texas Instruments Incorporated
Product Folder Links: LM2695
LM2695
www.ti.com
SNVS413A –JANUARY 2006–REVISED APRIL 2013
APPLICATIONS INFORMATION
EXTERNAL COMPONENTS
The following guidelines can be used to select the external components.
R1 and R2: The ratio of these resistors is calculated from:
R1/R2 = (VOUT/2.5V) - 1
(9)
R1 and R2 should be chosen from standard value resistors in the range of 1.0 kΩ - 10 kΩ which satisfy the
above ratio.
RON: The minimum value for RON is calculated from:
200 ns x VIN(MAX)
RON
í
1.3 x 10-10
(10)
Equation 1 can be used to select RON if a specific frequency is desired as long as the above limitation is met.
L1: The main parameter affected by the inductor is the output current ripple amplitude (IOR). The limits for IOR
must be determined at both the minimum and maximum nominal load currents.
a) If the maximum load current is less than the current limit threshold (1.25A), the minimum load current is used
to determine the maximum allowable ripple. To maintain continuous conduction mode the lower peak should not
reach 0 mA. For this case, the maximum ripple current is:
IOR(MAX1) = 2 x IO(min)
(11)
The ripple calculated in Equation 11 is then used in the following equation:
VOUT x (VIN - VOUT
IOR x FS x VIN
)
L1 =
where
•
•
VIN is the maximum input voltage
Fs is determined from Equation 1
(12)
This provides a minimum value for L1. The next larger standard value should be used, and L1 should be rated
for the IPK current level.
b) If the maximum load current is greater than the current limit threshold (1.25A), the LM2695 ensures the lower
peak reaches 1.25A each cycle, requiring that IOR be at least twice the difference. The upper peak, however,
must not exceed 2A. For this case, the ripple limits are:
IOR(MAX2) = 2 x (2A - IO(max)
)
(13)
and
IOR(MIN1) = 2 x (IO(max) - 1.25A)
(14)
The lesser of Equation 13 and Equation 14 is then used in Equation 12. If IOR(MAX2) is used, the maximum VIN is
used in Equation 12. The next larger value should then be used for L1. If IOR(MIN1) is used, the minimum VIN is
used in Equation 12. The next smaller value should then be used for L1. L1 must be rated for the peak value of
the current waveform (IPK in Figure 8).
C3: The capacitor at the VCC output provides not only noise filtering and stability, but also prevents false
triggering of the VCC UVLO at the buck switch on/off transitions. For this reason, C3 should be no smaller than
0.1 µF, and should be a good quality, low ESR, ceramic capacitor.
C2, and R3: Since the LM2695 requires a minimum of 25 mVp-p of ripple at the FB pin for proper operation, the
required ripple at VOUT1 is increased by R1 and R2. This necessary ripple is created by the inductor ripple current
acting on C2’s ESR + R3. The minimum ripple current is calculated using Equation 12, rearranged to solve for
IOR at minimum VIN. The minimum ESR for C2 is then equal to:
25 mV x (R1 + R2)
ESR(min)
=
R2 x IOR(min)
(15)
11
Copyright © 2006–2013, Texas Instruments Incorporated
Submit Documentation Feedback
Product Folder Links: LM2695
LM2695
SNVS413A –JANUARY 2006–REVISED APRIL 2013
www.ti.com
If the capacitor used for C2 does not have sufficient ESR, R3 is added in series as shown in Typical Application
Circuit and Block Diagram. Generally R3 is less than 1Ω. C2 should generally be no smaller than 3.3 µF,
although that is dependent on the frequency and the allowable ripple amplitude at VOUT1. 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.
D1: The important parameters are reverse recovery time and forward voltage. The reverse recovery time
determines how long the reverse current surge lasts each time the buck switch is turned on. The forward voltage
drop is significant in the event the output is short-circuited as it is mainly this diode’s voltage (plus the voltage
across the current limit sense resistor) which forces the inductor current to decrease during the off-time. For this
reason, a higher voltage is better, although that affects efficiency. A reverse recovery time of ≊30 ns, and a
forward voltage drop of ≊0.75V are preferred. The reverse leakage specification is important as that can
significantly affect efficiency. D1’s reverse voltage rating must be at least as great as the maximum VIN, and its
current rating must equal or exceed IPK Figure 8.
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. If the
source’s dynamic impedance is high (effectively a current source), it supplies the average input current, but not
the ripple current.
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 peak value, then drop 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. C1 is calculated from:
IO x tON
C1 =
DV
where
•
•
•
Io is the load current
tON is the maximum on-time
ΔV is the allowable ripple voltage at VIN
(16)
C5’s purpose is to help avoid transients and ringing due to long lead inductance at VIN. A low ESR, 0.1 µF
ceramic chip capacitor is recommended, located close to the LM2695.
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 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 reference voltage at the
regulation comparator, and the output voltage, to reach their final value. The time is determined from the
following:
C6 x 2.5V
tSS
=
12.3 mA
(17)
PC BOARD LAYOUT
The LM2695 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
current loop formed by D1, L1, C2 and the SGND and ISEN pins should be as small as possible. The ground
connection from C2 to C1 should be as short and direct as possible.
12
Submit Documentation Feedback
Copyright © 2006–2013, Texas Instruments Incorporated
Product Folder Links: LM2695
LM2695
www.ti.com
SNVS413A –JANUARY 2006–REVISED APRIL 2013
If it is expected that the internal dissipation of the LM2695 will produce excessive junction temperatures during
normal operation, good use of the PC board’s ground plane can help considerably to dissipate heat. The
exposed pad on the bottom of the IC package can be soldered to a ground plane, and that plane should extend
out from beneath the IC, and be connected to ground plane on the board’s other side with several vias, to help
dissipate the heat. The exposed pad is internally connected to the IC substrate. 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.
Copyright © 2006–2013, Texas Instruments Incorporated
Submit Documentation Feedback
13
Product Folder Links: LM2695
LM2695
SNVS413A –JANUARY 2006–REVISED APRIL 2013
www.ti.com
REVISION HISTORY
Changes from Original (April 2013) to Revision A
Page
•
Changed layout of National Data Sheet to TI format .......................................................................................................... 13
14
Submit Documentation Feedback
Copyright © 2006–2013, Texas Instruments Incorporated
Product Folder Links: LM2695
PACKAGE OPTION ADDENDUM
www.ti.com
16-Oct-2015
PACKAGING INFORMATION
Orderable Device
LM2695MH/NOPB
LM2695MHX/NOPB
LM2695SD/NOPB
LM2695SDX/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)
(6)
(3)
(4/5)
ACTIVE
HTSSOP
HTSSOP
WSON
PWP
14
14
10
10
94
Green (RoHS
& no Sb/Br)
CU SN
CU SN
CU SN
CU SN
Level-1-260C-UNLIM
Level-1-260C-UNLIM
Level-1-260C-UNLIM
Level-1-260C-UNLIM
L2695
MH
LIFEBUY
LIFEBUY
ACTIVE
PWP
DPR
DPR
2500
1000
4500
Green (RoHS
& no Sb/Br)
L2695
MH
Green (RoHS
& no Sb/Br)
L2695SD
WSON
Green (RoHS
& no Sb/Br)
L2695SD
(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.
(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
16-Oct-2015
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.
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
6-Nov-2015
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)
LM2695MHX/NOPB
LM2695SD/NOPB
LM2695SDX/NOPB
HTSSOP PWP
14
10
10
2500
1000
4500
330.0
178.0
330.0
12.4
12.4
12.4
6.95
4.3
5.6
4.3
4.3
1.6
1.3
1.3
8.0
8.0
8.0
12.0
12.0
12.0
Q1
Q1
Q1
WSON
WSON
DPR
DPR
4.3
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
6-Nov-2015
*All dimensions are nominal
Device
Package Type Package Drawing Pins
SPQ
Length (mm) Width (mm) Height (mm)
LM2695MHX/NOPB
LM2695SD/NOPB
LM2695SDX/NOPB
HTSSOP
WSON
PWP
DPR
DPR
14
10
10
2500
1000
4500
367.0
210.0
367.0
367.0
185.0
367.0
35.0
35.0
35.0
WSON
Pack Materials-Page 2
MECHANICAL DATA
PWP0014A
MXA14A (Rev A)
www.ti.com
MECHANICAL DATA
DPR0010A
SDC10A (Rev A)
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：
©2020 ICPDF网 联系我们和版权申明