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LX1995
TM (R)
Miniature LED Driver
PRODUCTION DATA SHEET
DESCRIPTION
KEY FEATURES Tiny 5-Pin TSOT Package Smallest External Components Efficient even at low current levels Logic Controlled Shutdown < 1A Shutdown Current > 85% Maximum Efficiency 70A Typical Quiescent Supply Current
APPLICATIONS
The LX1995 is a small sized step-up boost converter available in a Tiny TSOT-5 package suitable for driving adjustable boost topologies, which include drivers for white or color LEDs in portable devices. The LX1995 switches at rates up to 2 MHz to allow the use of extremely small inductor and filter capacitor. The LX1995 is available in two versions, 1 and 2, capable of driving 6 or 10 white LEDs, respectively. Designed for maximum efficiency over a wide output power range, the LX1995 is ideal for displays with day and night usage. The LX1995 features a pseudo-hysteretic pulse frequency modulation that promotes improved performance in battery-operated systems by operating with a quiescent
supply current <70A (typical) and a shutdown current of less than 1A. The input voltage range is from 1.6V to 5.5V thus allowing for a broad selection of battery voltage applications and start-up is guaranteed at 1.6V input. The output current is readily programmed using one external current sense resistor in series with the LEDs. This configuration provides a feedback signal to the FB pin thus maintaining constant output current regardless of varying input voltage and LED forward voltage (VF). Dimming may be accomplished by PWM modulating the shutdown input; the fast response time and stability of the PFM modulation circuit allows PWM dimming to low duty cycles. The LX1995 is available in the 5-Pin TSOT and thus requires a very small PCB area.
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Pagers Wireless Phones PDAs Handheld Computers LED Driver Digital Camera Displays GPS Receivers
IMPORTANT: For the most current data, consult MICROSEMI's website: http://www.microsemi.com
PRODUCT HIGHLIGHT
VBAT = 2.0V to 5.0V
IN SW
LX1995
ON OFF
SHDN GND FB
LX1995 LX1995
PACKAGE ORDER INFO
TA (C) -40 to 85 -40 to 85
Switch Current 325mA 500mA
SG 5-Pin
Plastic TSOT
SE 5-Pin
Plastic SOT-23 LX1995-1-CSE LX1995-2-CSE
LX1995-1-CSG LX1995-2-CSG
Note: Available in Tape & Reel. Append the letter "T" to the part number. (i.e. LX1995-CSGT)
Copyright 2000 Rev. 1.0, 2004-04-29
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
LX1995
TM (R)
Miniature LED Driver
PRODUCTION DATA SHEET
ABSOLUTE MAXIMUM RATINGS
PACKAGE PIN OUT
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Supply Input Voltage ........................................................................-0.3V to 7.0V Feedback Peak Pulse Input Voltage (VFB) .........................................-0.3V to 16V Shutdown Input Voltage (V SHDN ) ...........................................-0.3V to VIN + 0.3V Switch Voltage (VSW) ........................................................................-0.3V to 30V Switch Current (ISW) ...................................................................................500mA Operating Temperature Range .........................................................-40C to 85C Maximum Operating Junction Temperature ................................................ 125C Storage Temperature Range...........................................................-65C to 150C Lead Temperature (Soldering 10 seconds) .................................................. 235C
Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground. Currents are positive into, negative out of specified terminal.
SW
1
5
IN
GND
2
FB
3
4
SHDN
SG PACKAGE
(Top View)
SW GND FB
1 2
5
IN
THERMAL DATA
3
4
SHDN
SG SE
Plastic TSOT 5-Pin 207C/W
SE PACKAGE
(Top View)
THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA
Plastic SOT-23 5-Pin 191C/W
THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA
Junction Temperature Calculation: TJ = TA + (PD x JA). The JA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow.
FUNCTIONAL PIN DESCRIPTION Name SW GND FB Description Inductor Switching Connection - Internally connected to the drain of a 28V N-channel MOSFET. SW is high impedance in shutdown. Common terminal for ground reference. Feedback Input - Connect to a current sense resistor between the load and GND to set the maximum output current. FB pin is regulated to 320mV. Active-Low Shutdown Input - A logic low shuts down the device and reduces the supply current to <1A. Connect SHDN to VCC for normal operation. Unregulated IC Supply Voltage Input - Input range from +2.0V to +5.5V. Bypass with a 1F or greater capacitor for low voltage operation.
SHDN
IN
PACKAGE DATA PACKAGE DATA
Copyright 2000 Rev. 1.0, 2004-04-29
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
LX1995
TM (R)
Miniature LED Driver
PRODUCTION DATA SHEET
Unless otherwise specified, the following specifications apply over the operating ambient1 temperature 0C TA 70C except where otherwise noted and the following test conditions: VIN = 3V, V SHDN = VIN. Unless where indicated, these parameters apply to both the LX1995-1 and LX1995-2 part versions. Parameter Operating Voltage Minimum Start-up Voltage Start-up Voltage Temperature Coefficient Quiescent Current FB Threshold Voltage FB Input Bias Current Shutdown Input Bias Current Shutdown Low Input Voltage Shutdown High Input Voltage Switch Peak Current Switch Peak Current Minimum Switch Off-Time Switch Pin Leakage Current
Note: 1. 2.
ELECTRICAL CHARACTERISTICS
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Symbol VIN VSU kVST IQ VFB(TH) IFB I SHDN V SHDN IPEAK IPEAK tOFF ILEAK
Test Conditions
Min 1.6
LX1995 Typ
Max 5.5 1.6
Units V V mV/C
TA = +25C Guaranteed; not tested Not switching V SHDN < 0.4V Not Switching, VFB = 400mV V SHDN = 0V 288 -10 -100 1.4 250 400 -2 70 0.2 320
100 0.5 352 10 100 0.6 400 600
A mV nA nA V mA mA ns A
L= 47H; LX1995-1 L= 47H; LX1995-2 TA = +25C; VFB < VFB(TH) VSW = 28V
325 500 300 0.23
Low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient temperature. Functionality over the -40C to +85C operating temperature range is assured by design, characterization, and correlation.
ELECTRICALS ELECTRICALS
Copyright 2000 Rev. 1.0, 2004-04-29
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
LX1995
TM (R)
Miniature LED Driver
PRODUCTION DATA SHEET
SIMPLIFIED BLOCK DIAGRAM
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SW FB
Control Logic Driver
GND
V
SHDN
Bias
Reference
IN
Figure 1 - Simplified Block Diagram
APPLICATION CIRCUITS
L1 VBAT = 2.0V to 5.0V
10H 1206 Case Size
D1
1 0.1F
C
IN
SW
LX1995
100Hz to 1kHz
SHDN GND FB
ELECTRICALS ELECTRICALS
1 15
R
Figure 2 - Typical Bust Mode Dimming LED Driver Application
Copyright 2000 Rev. 1.0, 2004-04-29
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
LX1995
TM (R)
Miniature LED Driver
PRODUCTION DATA SHEET
APPLICATION CIRCUITS
WWW .Microsemi .C OM
L1 VBAT = 2.0V to 5.5V
10H 1206 Case Size
D1
1 0.1F
C
IN
SW
LX1995
ON OFF
SHDN GND FB
3 100k
R
2 17.4k
R
VDC = 0V to 2.0V ILED = 0mA to 20mA
Figure 3 - Analog Voltage Dimming LED Driver Application
1 17.4
R
L1 VBAT = 2.0V to 5.0V
10H 1206 Case Size
D1
1 0.1F
C
IN
SW
LX1995
ON OFF
SHDN GND FB
>10kHz VPWM = 3.3V DC = 10% to 90% ILED = 0mA to 20mA
4 9.09k
R
APPLICATIONS APPLICATIONS
0.1F
C2
3 90.9k
R
2 11.2k
R
1 15
R
Figure 4 - PWM to Analog Voltage Dimming LED Driver Application
The component values shown are only examples for a working system. Actual values will vary greatly depending on desired parameters, efficiency, and layout constraints.
Copyright 2000 Rev. 1.0, 2004-04-29
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
LX1995
TM (R)
Miniature LED Driver
PRODUCTION DATA SHEET
APPLICATION CIRCUITS
L1
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VBAT = 2.0V to 5.0V
10H 1206 Case Size SW IN
C1 .1F
On Off
LX1995
FB SHDN GND
320mV
2R - RA VCC
RA RCS
2R R RA = (0.64 x R) / VCC
LSB VCC MSB
MSB 1 1 0 0
LSB 1 0 1 0
ILED 0.25 x IMAX 0.50 x IMAX 0.75 x IMAX IMAX
Rcs = (0.32 x R) / {[R - (0.375 x RA)] x IMAX}
Figure 5 - Binary Dimming LED Driver Application The component values shown are only examples for a working system. Actual values will vary greatly depending on desired parameters, efficiency, and layout constraints
APPLICATIONS APPLICATIONS
Copyright 2000 Rev. 1.0, 2004-04-29
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6
LX1995
TM (R)
Miniature LED Driver
PRODUCTION DATA SHEET
THEORY OF OPERATION
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OPERATING THEORY The LX1995 is a PFM boost converter that is optimized for driving a string of series connected LEDs. It operates in a pseudo-hysteretic mode with a fixed switch "off time" of 300ns. Converter switching is enabled as LED current decreases causing the voltage at the FB pin to decrease to a value less than 320mV; this causes the feedback comparator (See Simplified Block Diagram) to activate the control logic. The control logic activates the DRV output circuit that connects to the gate of the internal N-Channel MOSFET. The switch output (SW) is switched "on" (and remains "on") until the inductor current ramps up to the peak current level (typically 325mA for LX1995-1). The LED load is powered from energy stored in the output capacitor during the inductor charging cycle. Once the peak inductor current value is achieved, the output is turned off (off-time is typically 300ns) allowing a portion of the energy stored in the inductor to be delivered to the load. This causes the voltage to rise across the current setting resistor (R1) at the input to the feedback circuit. The LX1995 continues to switch until the voltage at the FB pin exceeds 320mV. The value of R1 is established by dividing 320mV by the maximum series LED current. A minimum value of 3.3 is recommended for RSET. The voltage at the FB pin is the product of the LED current (ILED) and R1.
R1 = 320mV I LED( MAX)
INDUCTOR SELECTION AND OUTPUT CURRENT LIMIT PROGRAMMING The designer is encouraged to use inductors (for LX1995-1) that will not saturate at the peak inductor current level of 400mA. Larger inductor values will extend the power range of the converter slightly by increasing the average inductor current. Smaller inductor values will reduce output voltage ripple and are smaller in size. A range of 10uH to 47uH is recommended. OUTPUT RIPPLE AND CAPACITOR SELECTION Output voltage ripple is a function of the inductor value (L), output capacitor value (COUT), peak switch current (IPEAK), load current (IOUT), input voltage (VIN) and the output voltage (VOUT). When the switch is first turned on, the peak-to-peak voltage ripple is a function of the output droop (as the inductor current charges to IPEAK), the feedback transition error (i.e., typically 10mV), and the output overshoot (when the stored energy in the inductor is delivered to the load at the end of the charging cycle). Therefore the total ripple voltage is:
VRIPPLE = VDROOP + VOVERSHOOT+ 10mV
eq. 3
eq. 1
The initial droop can be estimated as follows where the 0.5V value in the denominator is an estimate of the voltage drop across the inductor and the FET RDS_ON:
DIMMING METHODS The designer can select one of two possible dimming methods. The first option is to connect a PWM logic signal to the SHDN pin (See Figure 1). This turns the LX1995 on and off which pulses the LED current between zero and the setting determined by R1; the human eye averages the pulsed current if the PWM frequency is greater than 60Hz. This option may not be ideal as short wavelength LEDs become less efficient when the forward current is pulsed. The second option is to apply a varying DC voltage to a voltage divider at the FB pin such that as the DC voltage increases, the LED current decreases. The equation (see Figure 3) is:
I LED = R2 + R3 R 1 - VADJ 2 320mV R R R1 3 3
L C (IPK x ILED ) VDROOP = OUT VIN - 0.5
eq. 4
The output overshoot can be estimated as follows where the 0.5 value in the denominator is an estimate of the voltage drop across the diode:
1 L (IPK - ILED )2 2 COUT VOVERSHOOT= VOUT - VIN + 0.5
APPLICATIONS APPLICATIONS
eq. 5
eq. 2
Once the output voltage ripple is determined for the selected components, the output capacitor can then be adjusted to meet the target ripple voltage requirements. Since the LX1995 is targeted for LED driver applications, output voltage ripple is not a critical application requirement.
Copyright 2000 Rev. 1.0, 2004-04-29
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
LX1995
TM (R)
Miniature LED Driver
PRODUCTION DATA SHEET
LX1995-1 EFFICIENCY
100 5.0V in 3.5V in 90
LX1995-2 EFFICIENCY
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100 5.0V IN 90 3.5V IN
Efficiency
70 47uH inductor, 4 White LEDs 60
Efficiency
80
80
70 47uH inductor, 4 White LEDs 60
50 2 4 6 8 10 12 14 16 18 20 LED Current
50 2 4 6 8 10 12 14 16 18 20 LED Current
C CHARTS
Copyright 2000 Rev. 1.0, 2004-04-29
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 8
LX1995
TM (R)
Miniature LED Driver
PRODUCTION DATA SHEET
PACKAGE DIMENSIONS
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SG
5-Pin Thin Shrink Small Outline Package (TSOT)
e
3
2
1
E
E1
4
b e1
5
D
A
A2 A1 L2
Dim A A1 A2 b C D E E1 e L L2
MILLIMETERS MIN MAX 1.00 0.01 0.10 0.84 0.90 0.30 0.45 0.12 0.20 2.90 BSC 2.80 BSC 1.60 BSC 0.95 BSC 0.30 0.40 0.25 BSC
INCHES MIN MAX 0.039 0.0004 0.004 0.033 0.035 0.012 0.018 0.005 0.008 0.114 BSC 0.110 BSC 0.063 BSC 0.037 BSC 0.012 0.016 0.010 BSC
C
L
SE
5-Pin Small Outline Package (SOT-23)
D G
H
E
A1
A C
B
F
J
I
K
Dim A A1 B C D E F G H I J K
MILLIMETERS MIN MAX 0.90 1.30 0.90 1.45 0.25 0.50 0.09 0.20 2.80 3.10 1.50 1.75 0.95 BSC 1.90 BSC 2.60 3.00 0.35 0.55 0.00 0.15 10 MAX
INCHES MIN MAX 0.035 0.051 0.035 0.057 0.010 0.020 0.004 0.008 0.110 0.122 0.059 0.069 0.038 BSC 0.075 BSC 0.102 0.118 0.014 0.022 0.000 0.006 10 MAX
M MECHANICALS
Note:
Dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(.006") on any side. Lead dimension shall not include solder coverage.
Copyright 2000 Rev. 1.0, 2004-04-29
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 9
LX1995
TM (R)
Miniature LED Driver
PRODUCTION DATA SHEET
NOTES
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NOTES NOTES
PRODUCTION DATA - Information contained in this document is proprietary to Microsemi and is current as of publication date. This document may not be modified in any way without the express written consent of Microsemi. Product processing does not necessarily include testing of all parameters. Microsemi reserves the right to change the configuration and performance of the product and to discontinue product at any time.
Copyright 2000 Rev. 1.0, 2004-04-29
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 10

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