LM27952SD/NOPB [TI]

输入电压范围为 3V 至 5.5V 的白光 LED 自适应 1.5X/1X 开关电容器电流驱动器 | NHK | 14 | -40 to 85;


型号：	LM27952SD/NOPB
厂家：	TEXAS INSTRUMENTS
描述：	输入电压范围为 3V 至 5.5V 的白光 LED 自适应 1.5X/1X 开关电容器电流驱动器 \| NHK \| 14 \| -40 to 85 开关驱动光电二极管接口集成电路电容器驱动器
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中文：	中文翻译
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LM27952

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SNVS364B –MAY 2005–REVISED MAY 2013

LM27952 White LED Adaptive 1.5X/1X Switched Capacitor Current Driver

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FEATURES

APPLICATIONS

•

Drives up to 4 LEDs with up to 30mA each

•

White LED Display Backlights

White LED Keypad Backlights

General Purpose LED Lighting

Regulated current sources with 0.2%(typ.)

matching

•

3/2x, 1x Gain transition based on LED V_F

Peak Efficiency Over 85%

DESCRIPTION

The LM27952 is a switched capacitor white-LED

driver capable of driving up to 4 LEDs with 30mA

through each LED. Its 4 tightly regulated current sinks

ensure excellent LED current and brightness

matching. LED drive current is programmed by an

external sense resistor. The LM27952 operates over

an input voltage range from 3.0V to 5.5V and requires

only four low-cost ceramic capacitors.

Input Voltage Range: 3.0V to 5.5V

PWM Brightness Control

Very Small Solution Size - NO INDUCTOR

Fixed 750kHz Switching Frequency

<1µA Shutdown Current

14-pin WSON Package: 4.0mm X 3.0mm X

0.8mm

The LM27952 provides excellent efficiency without

the use of an inductor by operating the charge pump

in a gain of 3/2, or in a gain of 1. Maximum efficiency

is achieved over the input voltage range by actively

selecting the proper gain based on the LED forward

voltage requirements.

Typical Application Circuit

= 3.0V - 5.5V

3.3 µF

OUT

C +

3.3 µF

OUT

1 µF

C -

C +

LM27952

C -

= 30 mA max

PWM

SET

GND

SET

Capacitors: 1 µF - TDK C1608X7R1A105K

3.3 µF - TDK C2012X7R1A335K

or equivalent

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.

LM27952

SNVS364B –MAY 2005–REVISED MAY 2013

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DESCRIPTION (CONTINUED)

The LM27952 uses constant frequency pre-regulation to minimize conducted noise on the input. It has a fixed

750kHz switching frequency optimized for portable applications. The LM27952 consumes less than 1µA of

supply current when shut down.

The LM27952 is available in a 14-pin No-Pullback Leadless Leadframe Package: WSON-14.

CONNECTION DIAGRAM

C2+

C1-

GND

C2-

C2+

GND

C2-

OUT

C1+

OUT

C1+

PWM

SET

Die-Attach Pad: GND

Top View

Bottom View

Figure 1. LM27952

14-pin No-Pullback Leadless Leadframe Package (WSON-14)

4mm x 3mm x 0.8mm

See Package Number NHK0014A

Pin Description

Name

C2+

V_OUT

C1+

Description

Flying Capacitor C2 Connection

Pre-Regulated Charge Pump Output

Flying Capacitor C1 Connection

Regulated Current Sink Input.

I_SET

Current Set Input. Placing a resistor (R_SET) between this pin and GND sets the LED current

for all the LEDs. LED Current = 200 x (1.25V ÷ R_SET).

Enable Logic Input Pin. Logic Low = Shut Down, Logic High = Enabled. There is a 150kΩ

(typ.) resistor connected internally between the EN pin and GND.

PWM

Current Sink Modulation Logic Input Pin. Logic Low = Off, Logic High = On.

Applying a Pulse Width Modulated (PWM) signal to this pin allows the regulated current sinks

to be modulated without shutting down the internal Charge Pump and the V_OUTnode.

V_IN

C2-

Input Supply Range: 3.0V to 5.5V.

Flying Capacitor C2 Connection.

Power Supply Ground Connection.

Flying Capacitor C1 Connection.

GND

C1-

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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(1) (2)(3)

Absolute Maximum Ratings

V_IN

-0.3V to 6.0V

EN, PWM

-0.3V to (V_IN+ 0.3V)

w/ 6.0V max

Continuous Power Dissipation

(4)

Internally Limited

150°C

Junction Temperature (T_J-MAX-ABS

Storage Temperature Range

Lead Temp. (Soldering, 5 sec.)

)

-65°C to 150°C

260°C

(5)

ESD Rating

Human Body Model

2kV

(1) Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under

which operation of the device is ensured. Operating Ratings do not imply ensured performance limits. For specified performance limits

and associated test conditions, see the Electrical Characteristics tables.

(2) All voltages are with respect to the potential at the GND pin.

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

availability and specifications.

(4) Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at T_J=150°C (typ.) and

disengages at T_J= 140°C (typ.).

(5) The Human-body model is a 100 pF capacitor discharged through a 1.5kΩ resistor into each pin.

(1) (2)

Operating Ratings

Input Voltage V_IN

3.0V to 5.5V

2.5V to 3.9V

LED Voltage Range

Junction Temperature Range (T_J)

-40°C to +115°C

Ambient Temperature Range (T_A)

(3)

-40°C to +85 °C

(1) All voltages are with respect to the potential at the GND pin.

(2) Min and Max limits are ensured by design, test, or statistical analysis. Typical numbers are not ensured, but do represent the most likely

norm.

(3) In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may

have to be derated. Maximum ambient temperature (T_A-MAX) is dependent on the maximum operation junction temperature (T_J-MAX-OP

115ºC), the maximum power dissipation of the device in the application (P_D-MAX), and the junction-to ambient thermal resistance of the

part/package in the application (θ_JA), as given by the following equation: T_A-MAX= T_J-MAX-OP- (θ_JA× P_D-MAX).

Thermal Characteristics

Junction-to-Ambient Thermal Resistance,

(1)

WSON-14 Package (θ_JA

)

45°C/W

(1) Junction-to-ambient thermal resistance (θ_JA) is taken from a thermal modeling result, performed under the conditions and guidelines set

forth in the JEDEC standard JESD51-7. The test board is a 4 layer FR-4 board measuring 102mm x 76mm x 1.6mm with a 2 x 1 array

of thermal vias. The ground plane on the board is 50mm x 50mm. Thickness of copper layers are 36µm/18µm

/18µm/36µm(1.5oz/1oz/1oz/1.5oz). Ambient temperature in simulation is 22°C, still air. Power dissipation is 1W. The value of θ_JAof the

LM27952 in WSON-14 could fall in a range as wide as 45ºC/W to 150ºC/W (if not wider), depending on PWB material, layout, and

environmental conditions. In applications where high maximum power dissipation exists (high V_IN, high I_OUT), special care must be paid

to thermal dissipation issues. For more information on these topics, please refer to Application Note 1187: Leadless Leadframe Package

(LLP) and the Power Efficiency and Power Dissipation section of this datasheet..

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(1) (2)

Electrical Characteristics

Limits in standard typeface are for T_A= 25°C, and limits in boldface type apply over the full operating junction temperature

range (-40°C to +85 °C). Unless otherwise noted, specifications apply to the LM27952 Typical Application Circuit (pg.1) with

(3)

V_IN= 3.6V, V(EN) = 1.8V, V(PWM) = 1.8V, 4 LEDs, V_DX= 0.45V, C_IN= C_OUT= 3.3µF, C₁= C₂= 1µF, R_SET= 12.5kΩ

Symbol

I_DX

Parameter

Conditions

Min

Typ

Max

Units

LED Current Regulation

3.0V ≤ V_IN≤ 5.5V

R_SET= 12.5kΩ

I_VOUT= 0mA

19.32

(−8%)

22.68

(+8%)

3.0V ≤ V_IN≤ 5.5V

R_SET= 8.32kΩ

I_VOUT= 0mA

3.0V ≤ V_IN≤ 5.5V

R_SET= 24.9kΩ

I_VOUT= 0mA

I_D-MATCH

I_Q

LED Current Matching

R_SET= 8.32kΩ

0.2

1.3

0.1

1.7

µA

(4)

Quiescent Supply Current

Shutdown Supply Current

I_SETPin Voltage

D_(1-4)= OPEN

R_SET= OPEN

I_SD

3.0V ≤ V_IN≤ 5.5V

V(EN) = 0V

V_SET

3.0V ≤ V_IN≤ 5.5V

1.25

200

I_DX/ I_SET

Output Current to Current Set

Ratio

V_HR

Current Sink Voltage

Headroom Requirement

I_DX= 95% I_DX(nom.)

R_SET= 8.32kΩ

(I_DXnom. = 31mA)

360

240

750

(5)

I_DX= 95% I_DX(nom.)

R_SET= 12.5kΩ

(I_DXnom. = 21mA)

f_SW

V_IH

V_IL

I_IH

Switching Frequency

Logic Input High

525

(-30%)

975

(+30%)

kHz

Input Pins: EN, PWM

3.0V ≤ V_IN≤ 5.5V

1.0

V_IN

Logic Input Low

Input Pins: EN, PWM

3.0V ≤ V_IN≤ 5.5V

0.4

Logic Input High Current

Input Pin: PWM

V(PWM) = 1.8V

µA

Ω

Input Pin: EN

V(EN) = 1.8V

(6)

I_IL

Logic Input Low Current

Charge Pump Output

Input Pins: EN, PWM

V(EN, PWM) = 0V

R_OUT

V_GDX

t_ON

3.3

450

330

(7)

Resistance

1x to 3/2x Gain Transition

Voltage Threshold on V_DX

V_DXFalling

µs

Startup Time

I_DX= 90% steady state

(1) All voltages are with respect to the potential at the GND pin.

(2) Min and Max limits are ensured by design, test, or statistical analysis. Typical numbers are not ensured, but do represent the most likely

norm.

(3) C_IN, C_OUT, C₁, C₂: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics

(4) LED Current Matching is based on two calculations: [(I_MAX- I_AVG) ÷ I_AVG] and [(I_AVG- I_MIN) ÷ I_AVG]. I_MAXand I_MINare the highest and

lowest respective Dx currents, and I_AVGis the average Dx current of all four current sinks. The largest number of the two calculations

(worst case) is considered the matching figure for the part. The typical specification provided is the most likely norm of the matching

figure for all parts.

(5) Headroom Voltage = V_DXto GND. If headroom voltage requirement is not met, LED current regulation will be compromised.

(6) EN Logic Input High Current (I_IH) is due to a 150kΩ (typ.) pull-down resistor connected internally between the EN and GND pins.

(7) The open loop output resistance (R_OUT) models all voltage losses in the charge pump. R_OUTcan be used to estimate the voltage at the

charge pump output V_OUTand the maximum current capability of the device under low V_INand high I_OUTconditions, beyond what is

specified in the electrical specifications table: V_OUT= (G x V_IN) - (R_OUTx I_OUT). In the equation, G is the charge pump gain mode, and

I_OUTis the total output current (sum of all active Dx current sinks and all current drawn from V_OUT).

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BLOCK DIAGRAM

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Typical Performance Characteristics

Unless otherwise specified: T_A= 25°C, 4 LEDs, V_DX= 0.45V, V_IN= 3.6V, V_EN= V_IN, V_PWM= V_IN, C₁= C₂= 1µF, C_IN= C_OUT

3.3µF. Capacitors are low-ESR multi-layer ceramic capacitors (MLCC's).

LED Current Regulation

vs.

LED Current Regulation

vs.

Input Voltage

Figure 2.

Figure 3.

Average LED Current Regulation

vs.

Input Voltage

Figure 4.

Figure 5.

Efficiency

vs.

Input Voltage

LED Current

vs.

R_SET

Figure 6.

Figure 7.

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Typical Performance Characteristics (continued)

Unless otherwise specified: T_A= 25°C, 4 LEDs, V_DX= 0.45V, V_IN= 3.6V, V_EN= V_IN, V_PWM= V_IN, C₁= C₂= 1µF, C_IN= C_OUT

3.3µF. Capacitors are low-ESR multi-layer ceramic capacitors (MLCC's).

LED Current

Output Voltage

vs.

Output Current

vs.

V_HR

Figure 8.

Figure 9.

Input and Output Voltage Ripple

Startup Response

V_IN= 3.6V, Load = 15mA/LED, 4 LEDs

CH1 (TOP): V_IN; Scale: 20mV/Div, AC Coupled

CH2 (BOTTOM): V_OUT; Scale: 20mV/Div, AC Coupled

V_IN= 3.6V, Load = 20mA/LED, 4 LEDs

CH1 (TOP): V_EN; Scale: 1V/Div

CH2 (BOTTOM): V_OUT; Scale: 1V/Div

Time scale: 400ns/Div

Time scale: 100µs/Div

Figure 10.

Figure 11.

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APPLICATION INFORMATION

CIRCUIT DESCRIPTION

The LM27952 is an adaptive 1.5x/1x CMOS charge pump, optimized for driving white LEDs used in backlighting

small-format displays. It provides four constant current inputs capable of sinking up to 30mA through each LED.

The well-matched current sinks ensure the current through all the LEDs are virtually identical, providing a uniform

brightness across the entire display.

Each LED is driven from V_OUTand connected to one of the four current sinks. LED drive current is programmed

by connecting a resistor, R_SET, to the current set pin, I_SET. LED brightness is adjusted by applying a Pulse Width

Modulated (PWM) signal to the dedicated PWM input pin.

CHARGE PUMP

The input to the 1.5x/1x charge pump is connected to the V_INpin, and the loosely regulated output of the charge

pump is connected to the V_OUTpin. The recommended input voltage range of the LM27952 is 3.0V to 5.5V. The

device's loosely-regulated charge pump has both open loop and closed loop modes of operation. When the

device is in open loop, the voltage at V_OUTis equal to the gain times the voltage at the input. When the device is

in closed loop, the voltage at V_OUTis loosely regulated to 4.5V (typ.). The charge pump gain transitions are

actively selected to maintain regulation based on LED forward voltage and load requirements. This allows the

charge pump to stay in the most efficient gain (1x) over as much of the input voltage range as possible, reducing

the power consumed from the battery.

SOFT START

The LM27952 contains internal soft-start circuitry to limit input inrush currents when the part is enabled. Soft start

is implemented internally with a controlled turn-on of the internal voltage reference. Due to the soft-start circuitry,

startup time of the LM27952 is approximately 330µs (typ.).

ENABLE AND PWM PINS

The LM27952 has 2 logic control pins. Both pins are active-high logic (HIGH = ON). There is an internal pull-

down resistor (150kΩ typ.) connected between the enable pin (EN) and GND. There is no pull-up or pull-down

connected to the Pulse Width Modulated (PWM) pin.

The EN pin is the master enable pin for the part. When the voltage on this pin is low (<0.4V), the part is in

shutdown mode. In this mode, all internal circuitry is OFF and the part consumes very little supply current (<1µA

typ.). When the voltage on the EN pin is high (>1.0V), the part will activate the charge pump and regulate the

output voltage to its nominal value.

The PWM pin serves as a dedicated logic input for LED brightness control. When the voltage on this pin is low

(<0.4V), the current sinks will be turned off and no current will flow through the LEDs. When the voltage on this

pin is high (>1.0V), the currents sinks will turn on and regulate to the current level set by the resistor connected

to the I_SETpin.

SETTING LED CURRENTS

The current through the four LEDs connected to D_1-4can be set to a desired level simply by connecting an

appropriately sized resistor (R_SET) between the I_SETpin of the LM27952 and GND. The LED currents are

proportional to the current that flows out of the I_SETpin and are a factor of 200 times greater than the I_SETcurrent.

The feedback loop of an internal amplifier sets the voltage of the I_SETpin to 1.25V (typ.). The statements above

are simplified in the equations below:

I_Dx= 200 ×(V_SET/ R_SET

)

(1)

(2)

R_SET= 200 × (1.25V / I_Dx

)

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ADJUSTING LED BRIGHTNESS (PWM control)

Perceived LED brightness can be adjusted using a PWM control signal on the LM27952 PWM logic input pin,

turning the current sources ON and OFF at a rate faster than perceptible by the eye. When this is done, the total

brightness perceived is proportional to the duty cycle (D) of the PWM signal (D = the percentage of time that the

LED is on in every PWM cycle). A simple example: if the LEDs are driven at 15mA each with a PWM signal that

has a 50% duty cycle, perceived LED brightness will be about half as bright as compared to when the LEDs are

driven continuously with 15mA.

The minimum recommended PWM frequency is 100Hz. Frequencies below this may be visibly noticeable as

flicker or blinking. The maximum recommended PWM frequency is 1kHz. Frequencies above this may cause

interference with internal current driver circuitry and/or noise in the audible range. Due to the regulation control

loop, the maximum frequency and minimum duty cycle applied to the PWM pin should be chosen such that the

minimum ON time is no less than 30µs in duration. If a PWM signal is applied to the EN pin instead, the

maximum frequency and minimum duty cycle should be chosen to accommodate both the LM27952 startup time

(330µs typ.) and the 30µs control loop delay.

The preferred method to adjust brightness is to keep the master EN voltage ON continuously and apply a PWM

signal to the dedicated PWM input pin. The benefit of this type of connection can be best understood with a

contrary example. When a PWM signal is connected to the master enable (EN) pin, the charge pump repeatedly

turns on and off. Every time the charge pump turns on, there is an inrush of current as the capacitances, both

internal and external, are recharged. This inrush current results in a current spike and a voltage dip at the input

of the part. By only applying the PWM signal to PWM logic input pin, the charge pump continuously stays on,

resulting in much lower input noise.

In cases where a PWM signal must be connected to the EN pin, measures can be taken to reduce the

magnitude of the charge-pump turn-on transient response. More input capacitance, series resistors and/or ferrite

beads may provide benefits. If the current spikes and voltage dips can be tolerated, connecting the PWM signal

to the EN pin does provide a benefit of lower supply current consumption. When the PWM signal to the EN pin is

low, the LM27952 will be shutdown and input current will only be a few micro-amps. This results in a lower time-

averaged input current than the prior suggestion, where EN is kept on continuously.

MAXIMUM OUTPUT CURRENT, MAXIMUM LED VOLTAGE, MINIMUM INPUT VOLTAGE

The LM27952 can drive 4 LEDs at 30mA each from an input voltage as low as 3.0V, so long as the LEDs have a

forward voltage of 3.5V or less (room temperature).

The statement above is a simple example of the LED drive capabilities of the LM27952. The statement contains

key application parameters required to validate an LED-drive design using the LM27952: LED current (I_LED),

number of active LEDs (N), LED forward voltage (V_LED), and minimum input voltage (V_IN-MIN).

The equation below can be used to estimate the total output current capability of the LM27952:

I_{LED_MAX}= ((1.5 x V_IN) - V_LED) / ((N x R_OUT) + k_HR) (eq. 1)

(3)

(4)

I_{LED_MAX}= ((1.5 x V_IN) - V_LED) / ((N x 3.3Ω) + 12mV/mA)

R_OUT– Output resistance. This parameter models the internal losses of the charge pump that result in voltage

droop at the pump output V_OUT. Since the magnitude of the voltage droop is proportional to the total output

current of the charge pump, the loss parameter is modeled as a resistance. The output resistance of the

LM27952 is typically 3.3Ω (V_IN= 3.0V, T_A= 25°C). In equation form:

V_VOUT= 1.5 × V_IN– N × I_LED× R_OUT

(eq. 2)

(5)

k_HR– Headroom constant. This parameter models the minimum voltage required across the current sinks for

proper regulation. This minimum voltage is proportional to the programmed LED current, so the constant has

units of mV/mA. The typical k_HRof the LM27952 is 12mV/mA. In equation form:

(V_VOUT– V_LED) > k_HR× I_LED

(eq. 3)

(6)

The "I_LED-MAX" equation (eq. 1) is obtained from combining the R_OUTequation (eq. 2) with the k_HRequation (eq. 3)

and solving for I_LED. Maximum LED current is highly dependent on minimum input voltage and LED forward

voltage. Output current capability can be increased by raising the minimum input voltage of the application, or by

selecting LEDs with a lower forward voltage. Excessive power dissipation may also limit output current capability

of an application.

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CAPACITOR SELECTION

The LM27952 requires 4 external capacitors for proper operation. Surface-mount multi-layer ceramic capacitors

are recommended. These capacitors are small, inexpensive and have very low equivalent series resistance (ESR

<20mΩ typ.). Tantalum capacitors, OS-CON capacitors, and aluminum electrolytic capacitors are not

recommended for use with the LM27952 due to their high ESR, as compared to ceramic capacitors.

For most applications, ceramic capacitors with X7R or X5R temperature characteristic are preferred for use with

the LM27952. These capacitors have tight capacitance tolerance (as good as ±10%) and hold their value over

temperature (X7R: ±15% over -55°C to 125°C; X5R: ±15% over -55°C to 85°C).

Capacitors with Y5V or Z5U temperature characteristic are generally not recommended for use with the

LM27952. Capacitors with these temperature characteristics typically have wide capacitance tolerance (+80%, -

20%) and vary significantly over temperature (Y5V: +22%, -82% over -30°C to +85°C range; Z5U: +22%, -56%

over +10°C to +85°C range). Under some conditions, a nominal 1µF Y5V or Z5U capacitor could have a

capacitance of only 0.1µF. Such detrimental deviation is likely to cause Y5V and Z5U capacitors to fail to meet

the minimum capacitance requirements of the LM27952.

The voltage rating of the output capacitor should be 10V or more. All other capacitors should have a voltage

rating at or above the maximum input voltage of the application.

PARALLEL DX OUTPUTS FOR INCREASED CURRENT DRIVE

Outputs D_1-4may be connected together to drive a one or two LEDs at higher currents. In such a configuration,

all four parallel current sinks of equal value drive the single LED. The LED current programmed should be

chosen so that the current through each of the outputs is programmed to 25% of the total desired LED current.

For example, if 60mA is the desired drive current for the single LED, R_SETshould be selected such that the

current through each of the current sink inputs is 15mA. Similarly, if two LEDs are to be driven by pairing up the

D_1-4inputs (i.e D_1-2, D_3-4), R_SETshould be selected such that the current through each current sink input is 50% of

the desired LED current.

Connecting the outputs in parallel does not affect internal operation of the LM27952 and has no impact on the

Electrical Characteristics and limits previously presented. The available diode output current, maximum diode

voltage, and all other specifications provided in the Electrical Characteristics table apply to this parallel output

configuration, just as they do to the standard 4-LED application circuit.

POWER EFFICIENCY

Efficiency of LED drivers is commonly taken to be the ratio of power consumed by the LEDs (PLED) to the power

drawn at the input of the part (PIN). With a 1.5x/1x charge pump, the input current is equal to the charge pump

gain times the output current (total LED current). For a simple approximation, the current consumed by internal

circuitry can be neglected and the efficiency of the LM27952 can be predicted as follows:

P_LED= N × V_LED× I_LED

P_IN= V_IN× I_IN

(7)

(8)

P_IN= V_IN× (Gain × N × I_LED+ I_Q)

E = (P_LED÷ P_IN)

(9)

(10)

Neglecting I_Qwill result in a slightly higher efficiency prediction, but this impact will be no more than a few

percentage points when several LEDs are driven at full power. It is also worth noting that efficiency as defined

here is in part dependent on LED voltage. Variation in LED voltage does not affect power consumed by the

circuit and typically does not relate to the brightness of the LED. For an advanced analysis, it is recommended

that power consumed by the circuit (V_INx I_IN) be evaluated rather than power efficiency.

THERMAL PROTECTION

Internal thermal protection circuitry disables the LM27952 when the junction temperature exceeds 150°C (typ.).

This feature protects the device from being damaged by high die temperatures that might otherwise result from

excessive power dissipation. The device will recover and operate normally when the junction temperature falls

below 140°C (typ.). It is important that the board layout provide good thermal conduction to keep the junction

temperature within the specified operating ratings.

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POWER DISSIPATION

The power dissipation (P_DISSIPATION) and junction temperature (T_J) can be approximated with the equations

below. P_INis the power generated by the 1.5x/1x charge pump, P_LEDis the power consumed by the LEDs, T_Ais

the ambient temperature, and θ_JAis the junction-to-ambient thermal resistance for the WSON-14 package. V_INis

the input voltage to the LM27952, V_LEDis the nominal LED forward voltage, and I_LEDis the programmed LED

current.

P_DISSIPATION= P_IN- P_LED

(11)

(12)

(13)

= [Gain × V_IN× (4 x I_LED)] − (V_LED× 4 x I_LED

)

T_J= T_A+ (P_DISSIPATION× θ_JA)

The junction temperature rating takes precedence over the ambient temperature rating. The LM27952 may be

operated outside the ambient temperature rating, so long as the junction temperature of the device does not

exceed the maximum operating rating of 115°C. The maximum ambient temperature rating must be derated in

applications where high power dissipation and/or poor thermal resistance causes the junction temperature to

exceed 115°C.

PCB Layout Considerations

The WSON is a leadframe based Chip Scale Package (CSP) with very good thermal properties. This package

has an exposed DAP (die attach pad) at the center of the package measuring 3.0mm x 1.6mm. The main

advantage of this exposed DAP is to offer lower thermal resistance when it is soldered to the thermal land on the

PCB. For PCB layout, TI highly recommends a 1:1 ratio between the package and the PCB thermal land. To

further enhance thermal conductivity, the PCB thermal land may include vias to a ground plane. For more

detailed instructions on mounting WSON packages, please refer to Texas Instruments Application Note AN-1187.

Submit Documentation Feedback

Product Folder Links: LM27952

LM27952

SNVS364B –MAY 2005–REVISED MAY 2013

www.ti.com

REVISION HISTORY

Changes from Revision A (May 2013) to Revision B

Page

•

Changed layout of National Data Sheet to TI format .......................................................................................................... 11

Submit Documentation Feedback

Product Folder Links: LM27952

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)

LM27952SD/NOPB

LM27952SDX/NOPB

ACTIVE

WSON

NHK

1000 RoHS & Green

4500 RoHS & Green

Level-1-260C-UNLIM

-40 to 85

D005B

⁽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

23-Sep-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)

LM27952SD/NOPB

LM27952SDX/NOPB

WSON

NHK

1000

4500

178.0

330.0

12.4

3.3

4.3

1.0

8.0

12.0

Pack Materials-Page 1

PACKAGE MATERIALS INFORMATION

www.ti.com

23-Sep-2013

*All dimensions are nominal

Device

Package Type Package Drawing Pins

SPQ

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

LM27952SD/NOPB

LM27952SDX/NOPB

WSON

NHK

1000

4500

210.0

367.0

185.0

367.0

35.0

Pack Materials-Page 2

MECHANICAL DATA

NHK0014A

SDA14A (Rev A)

www.ti.com

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TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATASHEETS), DESIGN RESOURCES (INCLUDING REFERENCE

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AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY

IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD

PARTY INTELLECTUAL PROPERTY RIGHTS.

These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate

TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable

standards, and any other safety, security, or other requirements. These resources are subject to change without notice. TI grants you

permission to use these resources only for development of an application that uses the TI products described in the resource. Other

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TI’s products are provided subject to TI’s Terms of Sale (www.ti.com/legal/termsofsale.html) or other applicable terms available either on

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Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265

LM27952SD/NOPB [TI]

相关型号：

LM27952SDX

LM27952SDX/NOPB

LM27952SDX/NOPB

LM27953

LM27953TL

LM27953TLX

LM2795BL

LM2795BLX

LM2795TL

LM2795TL/NOPB

LM2795TLX

LM2795TLX/NOPB