LM34910 [TI]
8V 至 36V、1.25A 恒定导通时间非同步降压稳压器;
| 型号： | LM34910 |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | 8V 至 36V、1.25A 恒定导通时间非同步降压稳压器 稳压器 |
| 文件： | 总20页 (文件大小：563K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LM34910
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SNVS297B –OCTOBER 2004–REVISED MARCH 2013
LM34910 High Voltage (40V, 1.25A) Step Down Switching Regulator
Check for Samples: LM34910
1
FEATURES
DESCRIPTION
The LM34910 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 40V N-Channel Buck Switch, and is
available in the thermally enhanced WSON-10
package. 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 40V, N-Channel Buck Switch
Integrated Start-Up Regulator
Input Voltage Range: 8V to 36V
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
•
•
WSON-10 (4 mm x 4 mm)
Exposed Thermal Pad For Improved Heat
Dissipation
TYPICAL APPLICATIONS
•
•
High Efficiency Point-Of-Load (POL) Regulator
Non-Isolated Telecommunication Buck
Regulator
•
Secondary High Voltage Post Regulator
Connection Diagram
SW
BST
ISEN
1
2
3
4
5
10
9
VIN
VCC
8
RON/SD
SS
SGND
RTN
7
6
FB
Figure 1. 10-Lead WSON
See DPR0010A Package
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 © 2004–2013, Texas Instruments Incorporated
LM34910
SNVS297B –OCTOBER 2004–REVISED MARCH 2013
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Typical Application Circuit and Block Diagram
7V SERIES
REGULATOR
8V-36V
Input
LM34910
V
VCC
IN
10
9
C3
VCC
THERMAL
UVLO
SHUTDOWN
C5
C1
-
RON
+
280 ns
OFF TIMER
ON TIMER
RON
SD
/
0.7V
8
RON
START
START
COMPLETE
COMPLETE
BST 2
GATE DRIVE
UVLO
C4
V
IN
2.5V
11.5 mA
DRIVER
LOGIC
SS
7
6
L1
LEVEL
SHIFT
C6
DRIVER
SW
1
VOUT1
+
-
FB
REGULATION
COMPARATOR
D1
CURRENT LIMIT
COMPARATOR
+
R3
-
ISEN
R1
3
4
VOUT2
OVER-VOLTAGE
COMPARATOR
2.875V
+
-
RSENSE
50 mW
-
+
RTN
5
62.5 mV
C2
SGND
R2
PIN DESCRIPTIONS
PIN
NAME
DESCRIPTION
APPLICATION INFORMATION
Internally connected to the buck switch source. Connect to
the external inductor, diode, and boost capacitor.
1
SW
Switching Node
Connect a 0.022 µF capacitor from SW to this pin. An
internal diode charges the capacitor during the off-time.
2
3
BST
ISEN
Boost pin for boot-strap capacitor
Internally the current sense resistor connects from this pin to
SGND. Re-circulating current flows out of this pin to the free-
wheeling diode. Current limit is set at 1.25A.
Current sense input
Re-circulating current flows into this pin to the current sense
resistor.
4
5
6
7
8
SGND
RTN
FB
Sense Ground
Circuit Ground
Feedback
Ground for all internal circuitry other than the current limit
detection.
Internally connected to the regulation and over-voltage
comparators. The regulation level is 2.5V.
An internal 11.5 µA current source charges an external
capacitor to 2.5V to provide the softstart function.
SS
Softstart
An external resistor from VIN to this pin sets the buck switch
on-time. Grounding this pin shuts down the regulator.
RON/SD
On-time Control and Shutdown
Nominally regulated to 7.0V. An external voltage (8V-14V)
can be connected to this pin to reduce internal dissipation.
9
VCC
VIN
Output from the start-up regulator
Input supply voltage
An internal diode connects VCC to VIN
.
10
Nominal input range is 8.0V to 36V.
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.
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SNVS297B –OCTOBER 2004–REVISED MARCH 2013
Absolute Maximum Ratings(1)(2)
VIN to GND
40V
BST to GND
50V
SW to GND (Steady State)
ESD Rating(3)
-1.5V
Human Body Model
2kV
BST to VCC
40V
VIN to SW
40V
BST to SW
14V
VCC to GND
14V
SGND to RTN
-0.3V to +0.3V
See Text
-0.3V to 4V
-0.3 to 7V
-55°C to +150°C
150°C
Current out of ISEN
SS to RTN
All Other Inputs to GND
Storage Temperature Range
JunctionTemperature
(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 guaranteed specifications and test conditions, see the Electrical Characteristics.
(2) For detailed information on soldering plastic WSON packages, refer to the Packaging Data Book available from National Semiconductor
Corporation.
(3) The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin.
Operating Ratings(1)
VIN
8.0V to 36V
Junction Temperature
−40°C to + 125°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 guaranteed specifications and test conditions, see the Electrical Characteristics.
Electrical Characteristics
Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply over full Operating Junction
(1)
Temperature range. VIN = 24V, RON = 200k unless otherwise stated
.
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
1.4
VCC = VCCReg - 100 mV
0 mA ≤ ICC ≤ 5 mA
VCC = 0V
VCC output impedance
VCC current limit(2)
140
9
Ω
mA
VCC under-voltage lockout
threshold
VCC increasing
UVLOVCC
5.8
V
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
0.63
80
1
mA
µA
250
Switch Characteristics
Rds(on)
UVLOGD
Buck Switch Rds(on)
ITEST = 200 mA
0.45
4.3
0.95
5.5
Ω
V
Gate Drive UVLO
VBST - VSW Increasing
3.0
UVLOGD hysteresis
440
mV
Softstart Pin
Pull-up voltage
2.5
V
Internal current source
11.5
µA
(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
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Electrical Characteristics (continued)
Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply over full Operating Junction
Temperature range. VIN = 24V, RON = 200k unless otherwise stated (1)
.
Symbol
Current Limit
ILIM
Parameter
Conditions
Min
Typ
Max
Units
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 = 36V, RON = 200 kΩ
Voltage at RON/SD rising
Voltage at RON/SD falling
2.1
2.75
740
0.65
40
3.6
1.1
µs
ns
V
tON - 2
On-time
Shutdown threshold
Threshold hysteresis
0.35
mV
Off Timer
tOFF
Minimum Off-time
280
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
2.875
100
2.550
V
V
nA
Thermal Shutdown
TSD Thermal shutdown temperature
Thermal shutdown hysteresis
175
20
°C
°C
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SNVS297B –OCTOBER 2004–REVISED MARCH 2013
Typical Performance Characteristics
7.5
7.0
6.5
6.0
5.5
5.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0
R
ON
= 400k
R
ON
= 200k
F
= 100 kHz
S
R
= 100k
ON
F
S
= 730 kHz
R
= 44.2k
ON
Load Current = 500 mA
0
10
20
(V)
30
40
6.5
7.0
7.5
8.0
(V)
8.5
9.0
V
IN
V
IN
Figure 2. VCC vs VIN
Figure 3. ON-Time vs VIN and RON
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Functional Description
The LM34910 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 40V N-
Channel buck switch, is easy to implement, and is available in the thermally enhanced WSON-10 package. 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 LM34910 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 LM34910 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 280 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 280 ns. Once regulation is
established, the off-times are longer.
When in regulation, the LM34910 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)
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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, requiring a minimum amount of ESR
for the output capacitor C2. The LM34910 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 4. However, R3 slightly degrades the load regulation.
L1
SW
LM34910
R1
R2
R3
FB
V
OUT2
C2
Figure 4. Low Ripple Output Configuration
Start-up Regulator, VCC
The start-up regulator is integral to the LM34910. The input pin (VIN) can be connected directly to line voltage up
to 36V, with transient capability to 40V. The VCC output regulates at 7.0V, and is current limited to 9 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 5.8V, 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
(≊5.7V), 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. See Figure 2.
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 50V. Internally, a
diode connects VCC to VIN. See Figure 5.
V
CC
C3
BST
SW
C4
L1
D2
LM34910
V
OUT1
D1
R3
R1
R2
I
SEN
V
OUT2
S
GND
C2
FB
Figure 5. Self Biased Configuration
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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 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. Bias current at the FB pin is nominally 100 nA.
Over-Voltage Comparator
The voltage at FB is compared to an internal 2.875V reference. If the voltage at FB rises above 2.875V 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 LM34910 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)
See Figure 3. The inverse relationship with VIN results in a nearly constant frequency as VIN is varied. RON should
be selected for a minimum on-time (at maximum VIN) greater than 200 ns. This requirement limits the maximum
frequency for each application, depending on VIN and VOUT, calculated from the following:
VOUT
FMAX
=
VINMAX x 200 ns
(6)
The LM34910 can be remotely shut down by taking the RON/SD pin below 0.65V. See Figure 6. 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.
V
IN
Input
Voltage
LM34910
RON
RON/SD
STOP
RUN
Figure 6. 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 may be lower
due to longer-than-normal off-times.
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Figure 7 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 7, 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
(7)
During this time the LM34910 is in a constant current mode, with an average load current (IOCL) equal to 1.25A +
ΔI/2.
I
PK
DI
I
OCL
1.25A
I
O
Load Current
Increases
Normal Operation
Current Limited
Figure 7. 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 3.5A. The
average current out of SW must be less than 3A, and the average current out of ISEN must be less than 2A.
Therefore IPK in Figure 7 must not exceed 3.5A, and IOCL must not exceed 2A.
N - Channel Buck Switch and Driver
The LM34910 integrates an N-Channel buck switch and associated floating high voltage gate driver. The peak
current allowed through the buck switch is 3.5A, and the maximum allowed average current is 3A. 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 280 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
11.5 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, if a thermal shutdown
occurs, or if the RON/SD pin is grounded.
Thermal Shutdown
The LM34910 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.
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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
(8)
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 VINMAX
RON
í
1.3 x 10-10
(9)
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)
(10)
The ripple calculated in Equation 10 is then used in the following equation:
VOUT x (VIN - VOUT
IOR x FS x VIN
)
L1 =
(11)
where VIN is the maximum input voltage and Fs is determined from Equation 1. 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 LM34910 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 3.5A. For this case, the ripple limits are:
IOR(MAX2) = 2 x (3.5A - IO(max)
)
(12)
and
IOR(MIN1) = 2 x (IO(max) - 1.25A)
(13)
The lesser of Equation 12 and Equation 13 is then used in Equation 11. If IOR(MAX2) is used, the maximum VIN is
used in Equation 11. The next larger value should then be used for L1. If IOR(MIN1) is used, the minimum VIN is
used in Equation 11. 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 7).
C3: The capacitor on 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 LM34910 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 11, 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)
(14)
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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 7.
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
(15)
where Io is the load current, tON is the maximum on-time, and ΔV is the allowable ripple voltage at VIN. 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 LM34910 .
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
=
11.5 mA
(16)
PC BOARD LAYOUT
The LM34910 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.
If it is expected that the internal dissipation of the LM34910 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 © 2004–2013, Texas Instruments Incorporated
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11
Product Folder Links: LM34910
LM34910
SNVS297B –OCTOBER 2004–REVISED MARCH 2013
www.ti.com
REVISION HISTORY
Changes from Revision A (March 2013) to Revision B
Page
•
Changed layout of National Data Sheet to TI format .......................................................................................................... 11
12
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Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM34910
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status Package Type Package Pins Package
Eco Plan
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
Samples
Drawing
Qty
(1)
(2)
(3)
(4/5)
(6)
LM34910SD/NOPB
LM34910SDX/NOPB
ACTIVE
ACTIVE
WSON
WSON
DPR
DPR
10
10
1000 RoHS & Green
4500 RoHS & Green
SN
Level-1-260C-UNLIM
Level-1-260C-UNLIM
-40 to 125
-40 to 125
34910SD
34910SD
SN
(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) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(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 finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two
lines if the finish value exceeds the maximum column width.
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 1
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
9-Aug-2022
TAPE AND REEL INFORMATION
REEL DIMENSIONS
TAPE DIMENSIONS
K0
P1
W
B0
Reel
Diameter
Cavity
A0
A0 Dimension designed to accommodate the component width
B0 Dimension designed to accommodate the component length
K0 Dimension designed to accommodate the component thickness
Overall width of the carrier tape
W
P1 Pitch between successive cavity centers
Reel Width (W1)
QUADRANT ASSIGNMENTS FOR PIN 1 ORIENTATION IN TAPE
Sprocket Holes
Q1 Q2
Q3 Q4
Q1 Q2
Q3 Q4
User Direction of Feed
Pocket Quadrants
*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)
LM34910SD/NOPB
LM34910SDX/NOPB
WSON
WSON
DPR
DPR
10
10
1000
4500
178.0
330.0
12.4
12.4
4.3
4.3
4.3
4.3
1.3
1.3
8.0
8.0
12.0
12.0
Q1
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
9-Aug-2022
TAPE AND REEL BOX DIMENSIONS
Width (mm)
H
W
L
*All dimensions are nominal
Device
Package Type Package Drawing Pins
SPQ
Length (mm) Width (mm) Height (mm)
LM34910SD/NOPB
LM34910SDX/NOPB
WSON
WSON
DPR
DPR
10
10
1000
4500
208.0
367.0
191.0
367.0
35.0
35.0
Pack Materials-Page 2
PACKAGE OUTLINE
DPR0010A
WSON - 0.8 mm max height
SCALE 3.000
PLASTIC SMALL OUTLINE - NO LEAD
4.1
3.9
A
B
(0.2)
4.1
3.9
PIN 1 INDEX AREA
FULL R
BOTTOM VIEW
SIDE VIEW
20.000
ALTERNATIVE LEAD
DETAIL
0.8
0.7
C
SEATING PLANE
0.08 C
0.05
0.00
EXPOSED
THERMAL PAD
2.6 0.1
(0.1) TYP
SEE ALTERNATIVE
LEAD DETAIL
5
6
2X
3.2
11
3
0.1
8X 0.8
1
10
0.35
0.25
0.1
10X
0.5
0.3
PIN 1 ID
10X
C A B
C
0.05
4218856/B 01/2021
NOTES:
1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing
per ASME Y14.5M.
2. This drawing is subject to change without notice.
3. The package thermal pad must be soldered to the printed circuit board for thermal and mechanical performance.
www.ti.com
EXAMPLE BOARD LAYOUT
DPR0010A
WSON - 0.8 mm max height
PLASTIC SMALL OUTLINE - NO LEAD
(2.6)
10X (0.6)
SYMM
10
1
10X (0.3)
(1.25)
SYMM
11
(3)
8X (0.8)
6
5
(
0.2) VIA
TYP
(1.05)
(R0.05) TYP
(3.8)
LAND PATTERN EXAMPLE
EXPOSED METAL SHOWN
SCALE:15X
0.07 MIN
ALL AROUND
0.07 MAX
ALL AROUND
EXPOSED
METAL
EXPOSED
METAL
SOLDER MASK
OPENING
METAL UNDER
SOLDER MASK
METAL
EDGE
SOLDER MASK
OPENING
NON SOLDER MASK
DEFINED
SOLDER MASK
DEFINED
(PREFERRED)
SOLDER MASK DETAILS
4218856/B 01/2021
NOTES: (continued)
4. This package is designed to be soldered to a thermal pad on the board. For more information, see Texas Instruments literature
number SLUA271 (www.ti.com/lit/slua271).
www.ti.com
EXAMPLE STENCIL DESIGN
DPR0010A
WSON - 0.8 mm max height
PLASTIC SMALL OUTLINE - NO LEAD
SYMM
10X (0.6)
METAL
TYP
(0.68)
10
1
10X (0.3)
(0.76)
11
SYMM
8X (0.8)
4X
(1.31)
5
6
(R0.05) TYP
4X (1.15)
(3.8)
SOLDER PASTE EXAMPLE
BASED ON 0.125 mm THICK STENCIL
EXPOSED PAD 11:
77% PRINTED SOLDER COVERAGE BY AREA
SCALE:20X
4218856/B 01/2021
NOTES: (continued)
5. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
design recommendations.
www.ti.com
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