TI LM2695 Lm2695 high voltage (30v, 1.25a) step down switching regulator Datasheet

LM2695
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LM2695 High Voltage (30V, 1.25A) Step Down Switching Regulator
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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.
1
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
TYPICAL APPLICATIONS
•
•
•
High Efficiency Point-Of-Load (POL) Regulator
Non-Isolated Telecommunication Buck
Regulator
Secondary High Voltage Post Regulator
PACKAGE
•
•
•
10-Pin WSON (4 mm x 4 mm)
14-Pin HTSSOP
Exposed Thermal Pad For Improved Heat
Dissipation
Basic Step Down Regulator
8V - 30V
Input
VIN
VCC
C3
C1
LM2695
RON
BST
C4
L1
RON/SD
SHUTDOWN
VOUT
SW
D1
SS
R1
R3
ISEN
C2
C6
FB
RTN
SGND
R2
1
2
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.
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.
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Connection Diagram
1
2
3
4
5
6
7
NC
NC
SW
VIN
BST
VCC
ISEN
RON/SD
SGND
SS
RTN
FB
NC
NC
14
1
13
2
12
3
11
4
10
5
SW
VIN
BST
VCC
ISEN
RON/SD
SGND
SS
RTN
FB
10
9
8
7
6
9
8
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
Application Information
WSON-10
HTSSOP-14
1
2
SW
Switching Node
Internally connected to the buck switch source.
Connect to the inductor, free-wheeling diode, and
bootstrap capacitor.
2
3
BST
Boost pin for bootstrap capacitor
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.
3
4
ISEN
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 1.25A.
4
5
SGND
Sense Ground
Re-circulating current flows into this pin to the current
sense resistor.
5
6
RTN
Circuit Ground
Ground for all internal circuitry other than the current
limit detection.
6
9
FB
Feedback input from the regulated
output
Internally connected to the regulation and overvoltage comparators. The regulation level is 2.5V.
7
10
SS
Softstart
An internal 12.3 µA current source charges an
external capacitor to 2.5V, providing the softstart
function.
8
11
RON/SD
On-time control and shutdown
An external resistor from VIN to this pin sets the buck
switch on-time. Grounding this pin shuts down the
regulator.
9
12
VCC
Output from the startup regulator
Nominally regulates at 7.0V. An external voltage (8V14V) can be applied to this pin to reduce internal
dissipation. An internal diode connects VCC to VIN.
13
VIN
Input supply voltage
Nominal input range is 8.0V to 30V.
1,7,8,14
NC
No connection.
No internal connection.
EP
Exposed Pad
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.
10
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
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Absolute Maximum Ratings (1) (2) (3)
VIN to RTN
33V
BST to RTN
47V
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
Current out of ISEN
See Text
SS to RTN
-0.3V to 4V
All Other Inputs to RTN
-0.3 to 7V
Storage Temperature Range
-65°C to +150°C
Junction Temperature
(1)
(2)
(3)
(4)
150°C
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.
For detailed information on soldering plastic WSON-10 packages, refer to the Packaging Data Book available from TI.
If Military/Aerospace specified devices are required, please contact the TI Sales Office/Distributors for availability and specifications.
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.
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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
Typ
Max
Units
6.6
7
7.4
V
Start-Up Regulator, VCC
VCCReg
UVLOVCC
VCC regulated output
VIN-VCC dropout voltage
ICC = 0 mA,
VCC = UVLOVCC + 250 mV
1.3
V
VCC output impedance
0 mA ≤ ICC ≤ 5 mA
140
Ω
VCC current limit (2)
VCC = 0V
9.7
mA
VCC under-voltage lockout
threshold
VCC increasing
5.7
UVLOVCC hysteresis
VCC decreasing
150
mV
UVLOVCC filter delay
100 mV overdrive
3
µs
IIN operating current
Non-switching, FB = 3V
0.5
0.8
mA
IIN shutdown current
RON/SD = 0V
95
200
µA
0.33
0.7
Ω
4.4
5.5
V
Switch Characteristics
Rds(on)
Buck Switch Rds(on)
ITEST = 200 mA
UVLOGD
Gate Drive UVLO
VBST - VSW Increasing
3.0
UVLOGD hysteresis
480
V
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
1.5
A
Resistance from ISEN to SGND
130
mΩ
Response time
150
ns
On Timer
tON - 1
On-time
VIN = 10V, RON = 200 kΩ
tON - 2
On-time
VIN = 30V, RON = 200 kΩ
Shutdown threshold
Voltage at RON/SD rising
Threshold hysteresis
Voltage at RON/SD falling
2.1
2.8
3.6
950
0.45
0.8
µs
ns
1.2
V
37
mV
250
ns
Off Timer
tOFF
Minimum Off-time
Regulation and Over-Voltage Comparators (FB Pin)
VREF
FB regulation threshold
SS pin = steady state
FB over-voltage threshold
2.440
2.5
2.550
V
2.9
V
1
nA
Thermal shutdown temperature
175
°C
Thermal shutdown hysteresis
20
°C
FB bias current
Thermal Shutdown
TSD
Thermal Resistance
(1)
(2)
4
θJA
Junction to Ambient
0 LFPM Air Flow
Both Packages
37
θJC
Junction to Case
Both Packages
6.6
°C/W
°C/W
Typical specifications represent the most likely parametric norm at 25°C operation.
VCC provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading
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Typical Performance Characteristics
7.0
7.5
RON = 400k
6.0
FS = 150 kHz
ON-TIME (Ps)
VCC (V)
7.0
FS = 45 kHz
6.5
FS = 750 kHz
6.0
5.0
4.0
RON = 200k
3.0
RON = 100k
2.0
5.5
1.0 RON = 44.2k
0
5.0
6.5
7.0
7.5
8.0
8.5
9.0
10
0
20
30
VIN (V)
VIN (V)
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
UVLO
THERMAL
SHUTDOWN
C5
C1
RON
RON
/SD
ON TIMER
RON
START
COMPLETE
250 ns
OFF TIMER
+
0.8V
START
COMPLETE
BST
GATE DRIVE
UVLO
C4
VIN
2.5V
12.3 PA
SS
C6
DRIVER
FB +
REGULATION
COMPARATOR
+
OVER2.9V VOLTAGE
COMPARATOR
RTN
DRIVER
LOGIC
L1
LEVEL
SHIFT
SW
VOUT1
D1
CURRENT LIMIT
COMPARATOR
+
62.5 mV
+
ISEN
R1
RSENSE
50 m:
SGND
R2
R3
VOUT2
C2
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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 NChannel buck switch, is easy to implement, and is available in the thermally enhanced WSON-10 and HTSSOP14 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:
VOUT
tON
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 (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 =
RL x (RON)2
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
6
(4)
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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
R3
FB
VOUT2
R2
C2
Figure 5. Low Ripple Output Configuration
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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
LM2695
D2
SW
VOUT1
D1
ISEN
R3
R1
SGND
R2
C2
FB
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 =
8
VIN
(5)
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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:
RON =
VOUT
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
RON
LM2695
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.
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IPK
'I
IOCL
Inductor Current
1.25A
IO
Normal Operation
Load Current
Increases
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
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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:
RON
t
200 ns x VIN(MAX)
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)
L1 =
IOR x FS x VIN
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)
IOR(MIN1) = 2 x (IO(max) - 1.25A)
(14)
and
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)
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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 =
'V
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:
tSS =
C6 x 2.5V
12.3 PA
(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
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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.
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Copyright © 2006–2013, Texas Instruments Incorporated
Product Folder Links: LM2695
13
LM2695
SNVS413A – JANUARY 2006 – REVISED APRIL 2013
www.ti.com
REVISION HISTORY
Changes from Original (April 2013) to Revision A
•
14
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 13
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Product Folder Links: LM2695
PACKAGE OPTION ADDENDUM
www.ti.com
16-Oct-2015
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
LM2695MH/NOPB
ACTIVE
HTSSOP
PWP
14
94
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
L2695
MH
LM2695MHX/NOPB
LIFEBUY
HTSSOP
PWP
14
2500
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
L2695
MH
LM2695SD/NOPB
LIFEBUY
WSON
DPR
10
1000
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
L2695SD
LM2695SDX/NOPB
ACTIVE
WSON
DPR
10
4500
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 125
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
Samples
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
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
LM2695MHX/NOPB
HTSSOP
PWP
14
2500
330.0
12.4
LM2695SD/NOPB
WSON
DPR
10
1000
178.0
LM2695SDX/NOPB
WSON
DPR
10
4500
330.0
6.95
5.6
1.6
8.0
12.0
Q1
12.4
4.3
4.3
1.3
8.0
12.0
Q1
12.4
4.3
4.3
1.3
8.0
12.0
Q1
Pack Materials-Page 1
W
Pin1
(mm) Quadrant
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
HTSSOP
PWP
14
2500
367.0
367.0
35.0
LM2695SD/NOPB
WSON
DPR
10
1000
210.0
185.0
35.0
LM2695SDX/NOPB
WSON
DPR
10
4500
367.0
367.0
35.0
Pack Materials-Page 2
MECHANICAL DATA
PWP0014A
MXA14A (Rev A)
www.ti.com
MECHANICAL DATA
DPR0010A
SDC10A (Rev A)
www.ti.com
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