LM34910C [TI]

High Voltage (50V, 1.25A) Step Down Switching Regulator;


型号：	LM34910C
厂家：	TEXAS INSTRUMENTS
描述：	High Voltage (50V, 1.25A) Step Down Switching Regulator
文件：	总19页 (文件大小：848K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LM34910C

www.ti.com

SNVS517B –MAY 2007–REVISED MARCH 2013

LM34910C High Voltage (50V, 1.25A) Step Down Switching Regulator

Check for Samples: LM34910C

FEATURES

DESCRIPTION

The LM34910C 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 55V 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.

•

Integrated 55V, N-Channel Buck Switch

Integrated Start-Up Regulator

Input Voltage Range: 8V to 50V

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

BST

I_SEN

V_IN

V_CC

R_ON/SD

S_GND

RTN

10-Lead WSON

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.

LM34910C

SNVS517B –MAY 2007–REVISED MARCH 2013

www.ti.com

Typical Application Circuit and Block Diagram

7V SERIES

REGULATOR

8V-50V

Input

LM34910C

THERMAL

SHUTDOWN

UVLO

R_ON

280 ns

OFF TIMER

ON TIMER

R_ON

0.7V

^ONSTART

START

COMPLETE

BST

GATE DRIVE

UVLO

2.5V

11.5 mA

DRIVER

LOGIC

LEVEL

SHIFT

DRIVER

OUT1

REGULATION

COMPARATOR

OVER-

VOLTAGE

2.875V

COMPARATOR

CURRENT LIMIT

COMPARATOR

SEN

OUT2

R_SENSE

50 mW

RTN

62.5 mV

GND

PIN DESCRIPTIONS

Name

Description

Application Information

Internally connected to the buck switch source. Connect to

the external inductor, diode, and boost capacitor.

Switching Node

Connect a 0.022 µF capacitor from SW to this pin. An

internal diode charges the capacitor during the off-time.

BST

I_SEN

Boost pin for boot-strap capacitor

Internally the current sense resistor connects from this pin to

S_GND. 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.

S_GND

RTN

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.

Softstart

An external resistor from V_INto this pin sets the buck switch

on-time. Grounding this pin shuts down the regulator.

R_ON/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.

V_CC

V_IN

Output from the start-up regulator

Input supply voltage

An internal diode connects V_CCto V_IN

Nominal input range is 8.0V to 50V.

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.

Submit Documentation Feedback

Product Folder Links: LM34910C

LM34910C

www.ti.com

SNVS517B –MAY 2007–REVISED MARCH 2013

Absolute Maximum Ratings⁽¹⁾⁽²⁾

V_INto GND

55V

BST to GND

70V

SW to GND (Steady State)

ESD Rating⁽³⁾

-1.5V

Human Body Model

2kV

BST to V_CC

55V

V_INto SW

55V

BST to SW

14V

V_CCto GND

14V

S_GNDto 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 I_SEN

SS to RTN

All Other Inputs to GND

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 specifications and test conditions, see the Electrical Characteristics.

(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and

specifications.

(3) The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin.

Operating Ratings⁽¹⁾

V_IN

8.0V to 50V

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 specifications and test conditions, see the Electrical Characteristics.

Electrical Characteristics

Specifications with standard typeface are for T_J= 25°C, and those with boldface type apply over full Operating Junction

Temperature range. V_IN= 24V, R_ON= 200k unless otherwise stated⁽¹⁾

Symbol

Parameter

Conditions

Min

6.6

Typ

Max

7.4

Units

Start-Up Regulator, V_CC

V_CCReg

V_CCregulated output

I_CC= 0 mA,

V_IN-V_CCdropout voltage

1.4

V_CC= V_CCReg - 100 mV

0 mA ≤ I_CC≤ 5 mA

V_CC= 0V

V_CCoutput impedance

V_CCcurrent limit⁽²⁾

140

Ω

UVLO_VCC

V_CCunder-voltage lockout

threshold

V_CCincreasing

5.8

UVLO_VCChysteresis

UVLO_VCCfilter delay

I_INoperating current

I_INshutdown current

V_CCdecreasing

150

µs

100 mV overdrive

Non-switching, FB = 3V

R_ON/SD = 0V

0.63

µA

250

Switch Characteristics

Rds(on)

UVLO_GD

Buck Switch Rds(on)

I_TEST= 200 mA

0.45

4.3

0.95

5.5

Ω

Gate Drive UVLO

V_BST- V_SWIncreasing

3.0

UVLO_GDhysteresis

440

(1) Typical specifications represent the most likely parametric norm at 25°C operation.

(2) V_CCprovides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading

Submit Documentation Feedback

Product Folder Links: LM34910C

LM34910C

SNVS517B –MAY 2007–REVISED MARCH 2013

www.ti.com

Electrical Characteristics (continued)

Specifications with standard typeface are for T_J= 25°C, and those with boldface type apply over full Operating Junction

Temperature range. V_IN= 24V, R_ON= 200k unless otherwise stated⁽¹⁾

Symbol

Parameter

Conditions

Min

Typ

Max

Units

Softstart Pin

Pull-up voltage

2.5

Internal current source

11.5

µA

Current Limit

I_LIM

Threshold

Current out of I_SEN

1.25

130

150

1.5

Resistance from I_SENto S_GND

Response time

mΩ

On Timer

t_ON- 1

On-time

V_IN= 10V, R_ON= 200 kΩ

V_IN= 50V, R_ON= 200 kΩ

Voltage at R_ON/SD rising

Voltage at R_ON/SD falling

2.1

2.75

560

0.65

3.6

1.1

µs

t_ON- 2

On-time

Shutdown threshold

Threshold hysteresis

0.35

Off Timer

t_OFF

Minimum Off-time

280

Regulation and Over-Voltage Comparators (FB Pin)

V_REF

FB regulation threshold

FB over-voltage threshold

FB bias current

SS pin = steady state

2.440

2.5

2.875

100

2.550

Thermal Shutdown

T_SDThermal shutdown temperature

Thermal shutdown hysteresis

175

°C

Submit Documentation Feedback

Product Folder Links: LM34910C

LM34910C

www.ti.com

SNVS517B –MAY 2007–REVISED MARCH 2013

Typical Performance Characteristics

7.5

7.0

6.5

6.0

5.5

5.0

= 100 kHz

= 730 kHz

Load Current = 500 mA

6.5

7.0

7.5

8.0

(V)

8.5

9.0

Figure 1. V_CCvs V_IN

Figure 2. ON-Time vs V_INand R_ON

Submit Documentation Feedback

Product Folder Links: LM34910C

LM34910C

SNVS517B –MAY 2007–REVISED MARCH 2013

www.ti.com

Functional Description

The LM34910C 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

55V 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 V_IN. 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 LM34910C can be applied in numerous applications to efficiently regulate down higher voltages. Additional

features include: Thermal shutdown, V_CCunder-voltage lockout, gate drive under-voltage lockout, and maximum

duty cycle limiter.

Hysteretic Control Circuit Overview

The LM34910C 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 (R_ON). 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 LM34910C 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:

V_OUT

F_S=

1.3 x 10^-10x R_ON

(1)

The buck switch duty cycle is equal to :

t_ON

V_OUT

V_IN

DC =

t_ON+ t_OFF

(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:

V_OUT²x L1 x 1.18 x 10²⁰

F_S=

R_Lx (R_ON

)

where

•

R_L= the load resistance

(3)

The output voltage is set by two external resistors (R1, R2). The regulated output voltage is calculated as

follows:

V_OUT= 2.5 x (R1 + R2) / R2

(4)

Submit Documentation Feedback

Product Folder Links: LM34910C

LM34910C

www.ti.com

SNVS517B –MAY 2007–REVISED MARCH 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 LM34910C 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 3. However, R3 slightly degrades the load regulation.

LM34910C

OUT2

Figure 3. Low Ripple Output Configuration

Start-up Regulator, V_CC

The start-up regulator is integral to the LM34910C. The input pin (V_IN) can be connected directly to line voltage

up to 50V, with transient capability to 55V. The V_CCoutput regulates at 7.0V, and is current limited to 9 mA. Upon

power up, the regulator sources current into the external capacitor at V_CC(C3). When the voltage on the V_CCpin

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 V_CCUVLO falling threshold

(≊5.7V), and the frequency. When V_CCfalls below the falling threshold the V_CCUVLO activates to shut off the

output. If V_CCis externally loaded, the minimum input voltage increases since the output impedance at V_CCis

≊140Ω. See Figure 1.

To reduce power dissipation in the start-up regulator, an auxiliary voltage can be diode connected to the V_CCpin.

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 (V_CC+ V_IN) cannot exceed 70V. Internally, a

diode connects V_CCto V_IN. See Figure 4.

BST

LM34910C

OUT1

SEN

OUT2

GND

Figure 4. Self Biased Configuration

Submit Documentation Feedback

Product Folder Links: LM34910C

LM34910C

SNVS517B –MAY 2007–REVISED MARCH 2013

www.ti.com

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 LM34910C is determined by the R_ONresistor and the input voltage (V_IN), and is calculated

from:

1.3 x 10^-10x R_ON

t_ON

V_IN

(5)

See Figure 2. The inverse relationship with V_INresults in a nearly constant frequency as V_INis varied. R_ONshould

be selected for a minimum on-time (at maximum V_IN) greater than 200 ns. This requirement limits the maximum

frequency for each application, depending on V_INand V_OUT, calculated from the following:

V_OUT

F_MAX

V_INMAXx 200 ns

(6)

The LM34910C can be remotely shut down by taking the R_ON/SD pin below 0.65V. See Figure 5. In this mode

the SS pin is internally grounded, the on-timer is disabled, and bias currents are reduced. Releasing the R_ON/SD

pin allows normal operation to resume. The voltage at the R_ON/SD pin is between 1.5V and 3.0V, depending on

V_INand the R_ONresistor.

Input

Voltage

LM34910C

R /SD

STOP

RUN

Figure 5. 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 S_GND, through the sense resistor, out of I_SENand 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 I_SENis 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.

Submit Documentation Feedback

Product Folder Links: LM34910C

LM34910C

www.ti.com

SNVS517B –MAY 2007–REVISED MARCH 2013

Figure 6 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 6, 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 = (V_IN- V_OUT) x t_ON/ L1

(7)

During this time the LM34910C is in a constant current mode, with an average load current (I_OCL) equal to 1.25A

+ ΔI/2.

OCL

1.25A

Load Current

Increases

Normal Operation

Current Limited

Figure 6. Inductor Current - Current Limit Operation

The current limit threshold can be increased by connecting an external resistor between S_GNDand I_SEN. The

external resistor will typically be less than 1Ω. The peak current out of SW and I_SENmust not exceed 3.5A. The

average current out of SW must be less than 3A, and the average current out of I_SENmust be less than 2A.

Therefore I_PKin Figure 6 must not exceed 3.5A, and I_OCLmust not exceed 2A.

N - Channel Buck Switch and Driver

The LM34910C 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 V_CCthrough 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 V_CCreaches 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 V_CCis below the under-voltage lockout threshold, if a thermal shutdown

occurs, or if the R_ON/SD pin is grounded.

Thermal Shutdown

The LM34910C 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.

Submit Documentation Feedback

Product Folder Links: LM34910C

LM34910C

SNVS517B –MAY 2007–REVISED MARCH 2013

www.ti.com

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 = (V_OUT/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.

R_ON: The minimum value for R_ONis calculated from:

200 ns x V_INMAX

R_ON

1.3 x 10^-10

(9)

Equation 1 can be used to select R_ONif 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 (I_OR). The limits for I_OR

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:

I_OR(MAX1)= 2 x I_O(min)

(10)

The ripple calculated in Equation 6 is then used in the following equation:

V_OUTx (V_IN- V_OUT

I_ORx F_Sx V_IN

)

L1 =

where

•

V_INis the maximum input voltage

Fs is determined from Equation 1

(11)

This provides a minimum value for L1. The next larger standard value should be used, and L1 should be rated

for the I_PKcurrent level.

b) If the maximum load current is greater than the current limit threshold (1.25A), the LM34910C ensures the

lower peak reaches 1.25A each cycle, requiring that I_ORbe at least twice the difference. The upper peak,

however, must not exceed 3.5A. For this case, the ripple limits are:

I_OR(MAX2)= 2 x (3.5A - I_O(max)

)

(12)

and

I_OR(MIN1)= 2 x (I_O(max)- 1.25A)

(13)

The lesser of Equation 12 and Equation 13 is then used in Equation 11. If I_OR(MAX2)is used, the maximum V_INis

used in Equation 11. The next larger value should then be used for L1. If I_OR(MIN1)is used, the minimum V_INis

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 (I_PKin Figure 6).

C3: The capacitor on the V_CCoutput provides not only noise filtering and stability, but also prevents false

triggering of the V_CCUVLO 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.

Submit Documentation Feedback

Product Folder Links: LM34910C

LM34910C

www.ti.com

SNVS517B –MAY 2007–REVISED MARCH 2013

C2, and R3: Since the LM34910C requires a minimum of 25 mV_p-pof ripple at the FB pin for proper operation,

the required ripple at V_OUT1is 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 I_ORat minimum V_IN. The minimum ESR for C2 is then equal to:

25 mV x (R1 + R2)

ESR_(min)

R2 x I_OR(min)

(14)

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 V_OUT1. 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 V_IN, and its

current rating must equal or exceed I_PKFigure 6.

C1 and C5: C1’s purpose is to supply most of the switch current during the on-time, and limit the voltage ripple

at V_IN, on the assumption that the voltage source feeding V_INhas 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 V_INsuddenly 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:

I_Ox t_ON

C1 =

where

•

Io is the load current

t_ONis the maximum on-time

ΔV is the allowable ripple voltage at V_IN

(15)

C5’s purpose is to help avoid transients and ringing due to long lead inductance at V_IN. A low ESR, 0.1 µF

ceramic chip capacitor is recommended, located close to the LM34910C .

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

t_SS

11.5 mA

(16)

Submit Documentation Feedback

Product Folder Links: LM34910C

LM34910C

SNVS517B –MAY 2007–REVISED MARCH 2013

www.ti.com

PC BOARD LAYOUT

The LM34910C 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 S_GNDand I_SENpins 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 LM34910C 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.

Submit Documentation Feedback

Product Folder Links: LM34910C

LM34910C

www.ti.com

SNVS517B –MAY 2007–REVISED MARCH 2013

REVISION HISTORY

Changes from Revision A (March 2013) to Revision B

Page

•

Changed layout of National Data Sheet to TI format .......................................................................................................... 12

Submit Documentation Feedback

Product Folder Links: LM34910C

PACKAGE OPTION ADDENDUM

www.ti.com

14-Feb-2014

PACKAGING INFORMATION

Orderable Device

LM34910CSD/NOPB

LM34910CSDE/NOPB

LM34910CSDX/NOPB

Status Package Type Package Pins Package

Eco Plan

Lead/Ball Finish

MSL Peak Temp

Op Temp (°C)

-40 to 125

Device Marking

Samples

Drawing

Qty

(1)

(2)

(6)

(3)

(4/5)

ACTIVE

WSON

DPR

1000

Green (RoHS

& no Sb/Br)

CU SN

Level-1-260C-UNLIM

L34910C

ACTIVE

DPR

250

Green (RoHS

& no Sb/Br)

-40 to 125

L34910C

4500

Green (RoHS

& no Sb/Br)

-40 to 125

⁽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.

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information

provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and

Addendum-Page 1

PACKAGE OPTION ADDENDUM

www.ti.com

14-Feb-2014

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

11-Oct-2013

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device

Package Package Pins

Type Drawing

SPQ

Reel

Pin1

Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant

(mm) W1 (mm)

LM34910CSD/NOPB

LM34910CSDE/NOPB

LM34910CSDX/NOPB

WSON

DPR

1000

250

178.0

330.0

12.4

4.3

1.3

8.0

12.0

4500

Pack Materials-Page 1

PACKAGE MATERIALS INFORMATION

www.ti.com

11-Oct-2013

*All dimensions are nominal

Device

Package Type Package Drawing Pins

SPQ

Length (mm) Width (mm) Height (mm)

LM34910CSD/NOPB

LM34910CSDE/NOPB

LM34910CSDX/NOPB

WSON

DPR

1000

250

210.0

367.0

185.0

367.0

35.0

4500

Pack Materials-Page 2

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

LM34910C [TI]

相关型号：

LM34910CSD

LM34910CSD/NOPB

LM34910CSD/NOPB

LM34910CSDE

LM34910CSDE/NOPB

LM34910CSDX

LM34910CSDX/NOPB

LM34910C_15

LM34910SD

LM34910SD/NOPB

LM34910SD/NOPB

LM34910SDX