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

LM27952 White LED Adaptive 1.5X/1X Switched Capacitor Current Driver LM27952 FEATURES APPLICATIONS
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
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2
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Drives up to 4 LEDs with up to 30mA each
Regulated current sources with 0.2%(typ.)
matching
3/2x, 1x Gain transition based on LED VF
Peak Efficiency Over 85%
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
White LED Display Backlights
White LED Keypad Backlights
General Purpose LED Lighting
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.
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
VIN = 3.0V - 5.5V
VIN
VOUT
D4
C 1+
CIN
3.3 µF
C1
3.3 µF
COUT
1 µF
D3
D2
C 1C 2+
D4
LM27952
C2
D1
D3
1 µF
D2
C 2-
D1
IDX = 30 mA max
ISET
PWM
GND
EN
RSET
Capacitors: 1 µF - TDK C1608X7R1A105K
3.3 µF - TDK C2012X7R1A335K
or equivalent
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
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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+
1
14
C1-
VOUT
2
13
GND
C1+
3
12
D4
4
D3
C1-
14
1
C2+
GND
13
2
VOUT
C2-
C2-
12
3
C1+
11
VIN
VIN
11
4
D4
5
10
PWM
PWM
10
5
D3
D2
6
9
EN
EN
9
6
D2
D1
7
8
ISET
ISET
8
7
D1
Die-Attach Pad: GND
Die-Attach Pad: GND
Bottom View
Top 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
Pin
Name
Description
1
C2+
Flying Capacitor C2 Connection
2
VOUT
Pre-Regulated Charge Pump Output
3
C1+
Flying Capacitor C1 Connection
4
D4
Regulated Current Sink Input.
5
D3
Regulated Current Sink Input.
6
D2
Regulated Current Sink Input.
7
D1
Regulated Current Sink Input.
8
ISET
Current Set Input. Placing a resistor (RSET) between this pin and GND sets the LED current
for all the LEDs. LED Current = 200 x (1.25V ÷ RSET).
9
EN
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.
10
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 VOUT node.
11
VIN
Input Supply Range: 3.0V to 5.5V.
12
C2-
Flying Capacitor C2 Connection.
13
GND
14
C1-
Power Supply Ground Connection.
Flying Capacitor C1 Connection.
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
2
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Absolute Maximum Ratings
(1) (2) (3)
VIN
-0.3V to 6.0V
EN, PWM
-0.3V to (VIN + 0.3V)
w/ 6.0V max
Continuous Power Dissipation
(4)
Internally Limited
Junction Temperature (TJ-MAX-ABS)
150°C
Storage Temperature Range
-65°C to 150°C
Lead Temp. (Soldering, 5 sec.)
260°C
ESD Rating (5)
Human Body Model
(1)
(2)
(3)
(4)
(5)
2kV
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.
All voltages are with respect to the potential at the GND pin.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office / Distributors for
availability and specifications.
Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ=150°C (typ.) and
disengages at TJ = 140°C (typ.).
The Human-body model is a 100 pF capacitor discharged through a 1.5kΩ resistor into each pin.
Operating Ratings
(1) (2)
Input Voltage VIN
3.0V to 5.5V
LED Voltage Range
2.5V to 3.9V
Junction Temperature Range (TJ)
-40°C to +115°C
Ambient Temperature Range (TA)
(3)
(1)
(2)
(3)
-40°C to +85 °C
All voltages are with respect to the potential at the GND pin.
Min and Max limits are ensured by design, test, or statistical analysis. Typical numbers are not ensured, but do represent the most likely
norm.
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 (TA-MAX) is dependent on the maximum operation junction temperature (TJ-MAX-OP =
115ºC), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the
part/package in the application (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP - (θJA × PD-MAX).
Thermal Characteristics
Junction-to-Ambient Thermal Resistance,
WSON-14 Package (θJA) (1)
(1)
45°C/W
Junction-to-ambient thermal resistance (θJA) 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 θJA of 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 VIN, high IOUT), 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 TA = 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
VIN = 3.6V, V(EN) = 1.8V, V(PWM) = 1.8V, 4 LEDs, VDX = 0.45V, CIN = COUT = 3.3µF, C1 = C2 = 1µF, RSET = 12.5kΩ (3)
Symbol
IDX
Parameter
Conditions
3.0V ≤ VIN ≤ 5.5V
RSET = 12.5kΩ
IVOUT = 0mA
LED Current Regulation
Min
Typ
Max
Units
19.32
(−8%)
21
22.68
(+8%)
mA
3.0V ≤ VIN ≤ 5.5V
RSET = 8.32kΩ
IVOUT = 0mA
31
3.0V ≤ VIN ≤ 5.5V
RSET = 24.9kΩ
IVOUT = 0mA
11
ID-MATCH
LED Current Matching
RSET = 8.32kΩ
0.2
1
%
IQ
Quiescent Supply Current
D(1-4) = OPEN
RSET = OPEN
1.3
1.7
mA
ISD
Shutdown Supply Current
3.0V ≤ VIN ≤ 5.5V
V(EN) = 0V
0.1
1
µA
VSET
ISET Pin Voltage
3.0V ≤ VIN ≤ 5.5V
1.25
IDX / ISET
Output Current to Current Set
Ratio
VHR
Current Sink Voltage
Headroom Requirement
(4)
(5)
V
200
IDX = 95% IDX (nom.)
RSET = 8.32kΩ
(IDX nom. = 31mA)
360
IDX = 95% IDX (nom.)
RSET = 12.5kΩ
(IDX nom. = 21mA)
240
525
(-30%)
fSW
Switching Frequency
VIH
Logic Input High
Input Pins: EN, PWM
3.0V ≤ VIN ≤ 5.5V
VIL
Logic Input Low
Input Pins: EN, PWM
3.0V ≤ VIN ≤ 5.5V
IIH
Logic Input High Current
Input Pin: PWM
V(PWM) = 1.8V
10
nA
Input Pin: EN
V(EN) = 1.8V
12
µA
10
nA
3.3
Ω
(6)
975
(+30%)
kHz
1.0
VIN
V
0
0.4
IIL
Logic Input Low Current
ROUT
Charge Pump Output
Resistance (7)
VGDX
1x to 3/2x Gain Transition
Voltage Threshold on VDX
VDX Falling
450
mV
tON
Startup Time
IDX = 90% steady state
330
µs
(1)
(2)
(3)
(4)
(5)
(6)
(7)
4
Input Pins: EN, PWM
V(EN, PWM) = 0V
750
mV
All voltages are with respect to the potential at the GND pin.
Min and Max limits are ensured by design, test, or statistical analysis. Typical numbers are not ensured, but do represent the most likely
norm.
CIN, COUT, C1, C2: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics
LED Current Matching is based on two calculations: [(IMAX - IAVG) ÷ IAVG] and [(IAVG - IMIN) ÷ IAVG]. IMAX and IMIN are the highest and
lowest respective Dx currents, and IAVG is 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.
Headroom Voltage = VDX to GND. If headroom voltage requirement is not met, LED current regulation will be compromised.
EN Logic Input High Current (IIH) is due to a 150kΩ (typ.) pull-down resistor connected internally between the EN and GND pins.
The open loop output resistance (ROUT) models all voltage losses in the charge pump. ROUT can be used to estimate the voltage at the
charge pump output VOUT and the maximum current capability of the device under low VIN and high IOUT conditions, beyond what is
specified in the electrical specifications table: VOUT = (G x VIN) - (ROUT x IOUT). In the equation, G is the charge pump gain mode, and
IOUT is the total output current (sum of all active Dx current sinks and all current drawn from VOUT).
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BLOCK DIAGRAM
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Typical Performance Characteristics
Unless otherwise specified: TA = 25°C, 4 LEDs, VDX = 0.45V, VIN = 3.6V, VEN = VIN, VPWM = VIN, C1 = C2 = 1µF, CIN = COUT =
3.3µF. Capacitors are low-ESR multi-layer ceramic capacitors (MLCC's).
6
LED Current Regulation
vs.
Input Voltage
LED Current Regulation
vs.
Input Voltage
Figure 2.
Figure 3.
Average LED Current Regulation
vs.
Input Voltage
Average LED Current Regulation
vs.
Input Voltage
Figure 4.
Figure 5.
Efficiency
vs.
Input Voltage
LED Current
vs.
RSET
Figure 6.
Figure 7.
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Typical Performance Characteristics (continued)
Unless otherwise specified: TA = 25°C, 4 LEDs, VDX = 0.45V, VIN = 3.6V, VEN = VIN, VPWM = VIN, C1 = C2 = 1µF, CIN = COUT =
3.3µF. Capacitors are low-ESR multi-layer ceramic capacitors (MLCC's).
LED Current
vs.
VHR
Output Voltage
vs.
Output Current
Figure 8.
Figure 9.
Input and Output Voltage Ripple
Startup Response
VIN = 3.6V, Load = 15mA/LED, 4 LEDs
CH1 (TOP): VIN; Scale: 20mV/Div, AC Coupled
CH2 (BOTTOM): VOUT; Scale: 20mV/Div, AC Coupled
Time scale: 400ns/Div
Figure 10.
VIN = 3.6V, Load = 20mA/LED, 4 LEDs
CH1 (TOP): VEN; Scale: 1V/Div
CH2 (BOTTOM): VOUT; Scale: 1V/Div
Time scale: 100µs/Div
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 VOUT and connected to one of the four current sinks. LED drive current is programmed
by connecting a resistor, RSET, to the current set pin, ISET. 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 VIN pin, and the loosely regulated output of the charge
pump is connected to the VOUT pin. 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 VOUT is equal to the gain times the voltage at the input. When the device is
in closed loop, the voltage at VOUT is 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 pulldown 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 ISET pin.
SETTING LED CURRENTS
The current through the four LEDs connected to D1-4 can be set to a desired level simply by connecting an
appropriately sized resistor (RSET) between the ISET pin of the LM27952 and GND. The LED currents are
proportional to the current that flows out of the ISET pin and are a factor of 200 times greater than the ISET current.
The feedback loop of an internal amplifier sets the voltage of the ISET pin to 1.25V (typ.). The statements above
are simplified in the equations below:
IDx = 200 ×(VSET / RSET)
RSET = 200 × (1.25V / IDx)
8
(1)
(2)
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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 timeaveraged 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 (ILED),
number of active LEDs (N), LED forward voltage (VLED), and minimum input voltage (VIN-MIN).
The equation below can be used to estimate the total output current capability of the LM27952:
ILED_MAX = ((1.5 x VIN) - VLED) / ((N x ROUT) + kHR) (eq. 1)
ILED_MAX = ((1.5 x VIN ) - VLED) / ((N x 3.3Ω) + 12mV/mA)
(3)
(4)
ROUT – Output resistance. This parameter models the internal losses of the charge pump that result in voltage
droop at the pump output VOUT. 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 (VIN = 3.0V, TA = 25°C). In equation form:
VVOUT = 1.5 × VIN – N × ILED × ROUT
(eq. 2)
(5)
kHR – 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 kHR of the LM27952 is 12mV/mA. In equation form:
(VVOUT – VLED) > kHR × ILED
(eq. 3)
(6)
The "ILED-MAX" equation (eq. 1) is obtained from combining the ROUT equation (eq. 2) with the kHR equation (eq. 3)
and solving for ILED. 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 D1-4 may 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, RSET should 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
D1-4 inputs (i.e D1-2, D3-4), RSET should 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:
PLED = N × VLED × ILED
PIN = VIN × IIN
PIN = VIN × (Gain × N × ILED + IQ)
E = (PLED ÷ PIN)
(7)
(8)
(9)
(10)
Neglecting IQ will 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 (VIN x IIN) 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.
10
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POWER DISSIPATION
The power dissipation (PDISSIPATION) and junction temperature (TJ) can be approximated with the equations
below. PIN is the power generated by the 1.5x/1x charge pump, PLED is the power consumed by the LEDs, TAis
the ambient temperature, and θJA is the junction-to-ambient thermal resistance for the WSON-14 package. VIN is
the input voltage to the LM27952, VLED is the nominal LED forward voltage, and ILED is the programmed LED
current.
PDISSIPATION = PIN - PLED
= [Gain × VIN × (4 x ILED)] − (VLED × 4 x ILED)
TJ = TA + (PDISSIPATION × θJA)
(11)
(12)
(13)
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.
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Copyright © 2005–2013, Texas Instruments Incorporated
Product Folder Links: LM27952
11
LM27952
SNVS364B – MAY 2005 – REVISED MAY 2013
www.ti.com
REVISION HISTORY
Changes from Revision A (May 2013) to Revision B
•
12
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 11
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Copyright © 2005–2013, Texas Instruments Incorporated
Product Folder Links: LM27952
PACKAGE OPTION ADDENDUM
www.ti.com
7-Oct-2013
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
(2)
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
LM27952SD/NOPB
ACTIVE
WSON
NHK
14
1000
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 85
D005B
LM27952SDX/NOPB
ACTIVE
WSON
NHK
14
4500
Green (RoHS
& no Sb/Br)
CU SN
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)
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.
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
Samples
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
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
LM27952SD/NOPB
WSON
NHK
14
1000
178.0
12.4
3.3
4.3
1.0
8.0
12.0
Q1
LM27952SDX/NOPB
WSON
NHK
14
4500
330.0
12.4
3.3
4.3
1.0
8.0
12.0
Q1
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
WSON
NHK
14
1000
210.0
185.0
35.0
LM27952SDX/NOPB
WSON
NHK
14
4500
367.0
367.0
35.0
Pack Materials-Page 2
MECHANICAL DATA
NHK0014A
SDA14A (Rev A)
www.ti.com
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