View STLD20D-C8_457554.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

(R)
STLD20D
WHITE LED POWER SUPPLY
PRELIMINARY DATA
ASDTM
FEATURES

APPLICATION

High efficiency above 80% Can drive up to 4 LEDs in series from 2.8V supply Constant LED current regulation Integrated LED disconnect switch that cuts the LEDs branch in shutdown mode Constant switching frequency Stable current regulation across the total input voltage range Supply voltage rejection Inherent soft start by limiting the peak inductor current Peak inductor current adjustability (STLD20DC8 only) Shutdown pin with possibility of PWM dimming control Over voltage and over temperature protection with automatic restart Low shutdown current < 1A Small external inductor (10H, height < 2mm) Tiny ceramic external capacitor Can be supplied by a Li-ion battery - VIN range: 2.5Vdc to 5Vdc
White Led supply for LCD backlight Mobile phone PDA and organizers Any handsets powered from 2.8V to 4.2V
DESCRIPTION The STLD20D is a constant switching frequency boost regulator with specific features to supply up to 4 white LEDs in series. A stable LED current regulation, from 2.8V to 4.2V, is achieved by sensing the LED current through a low ohmic shunt resistor RLED (see figure 1). The device also includes a supply rejection circuit that prevent any kind of flickering effect on the display during dynamic supply voltage variation. A LED disconnect switch cut the LED branch to reduce the current consumption in shutdown mode. The maximum peak inductor current can be programmed. The STLD20D includes often numerous features and innovative design circuit that allows getting an efficiency above 80% across the total supply voltage range. Figure 2: Efficiency versus input voltage (ILED=20mA; Tamb=25C)
Efficiency (%)
88
Figure 1: Basic connection
VBATT
L = 10H
D
87 86
Cin = 2.2F Cout = 1F
85 84 83
SW
VOUT RSET (*) RSET ILED = 20mA
82 81 80 79
VIN
STLD20D
LDS
FB SHDN
GND
RLED
D: STM BAT20J L: Murata LQH32CN100K33
(*) STLD20D-C8 only
78 2.5
3
3.5
4
4.5
5
Input voltage (Vdc)
Table 1: Order Codes Part Number STLD20D-C8 STLD20D-DEF Marking L2D L2D Package SOT23-8L QFN 3x3 8L
October 2004
REV. 2
1/8
This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to change without notice.
STLD20D
Figure 3: STLD20D-C8 Pin-Out Designation (SOT23-8L top view) Figure 4: STLD20D-DEF Pin-Out Designation (QFN 8L top view)
VIN SHDN RSET
VOUT LDS FB
VIN SHDN N/C
EXPOSED PAD
GND
SW
GND
SW VOUT LDS FB
1 GND
2 VIN
3
4
5 FB
6 LDS
7 VOUT
8 SW
1 GND
2 VIN
3 SHDN
4 N/C
5 FB
6 LDS
7 VOUT
8 SW
SHDN RSET
Figure 5: Block Diagram
SW
OTP OSCILLATOR RAMP OSCILLATOR COMPENSATION POWER FAULT ENABLE VIN OVP
VOUT
VIN
S
+ PWN COMP.
Q R
SW
SHDN
T VIN
LED DISCONNECT
+ DRAIN CURRENT REFERENCE
RSET (*) LDS LDS FB
VIN SHDN
+
LED CURRENT REFERENCE
GND
(*) STLD20D-C8 only
2/8
STLD20D
Table 2: External Components Pproposal (note 1) - Referred basic connection (figure 1) Symbol RLED CIN COUT L Parameter LED current resistance Input filtering capacitor Output capacitance Boost inductor (height < 2mm) Inductance Resistance at 500kHz Isat (RSET = 100k) D Boost diode (STMicroelectronics BAT20J type) VRRM IF (peak forward current) VF @ IF = 0.1A Tj = 25C IR @ Tj = 25C VR = 15V IR @ Tj = 85C VR = 15V 300 23 1 0.35 3 120 0.4 12 250 Ceramic type Test Conditions Value Min. Typ. Max. 15 2.2 1 10 1 H mA Vdc A V A Unit F
Note 1: the external components proposal should be considered as a design reference guide. The performances mentioned in the electrical characteristics table are not guaranteed for all the possible electrical parameters of the components included in this list. On an other hand the operation of STLD20D is not limited with the use of components included in this list.
Table 3: Absolute Maximum Ratings Symbol VIN VESD TOP Tstg BVDS SHDN Parameter Supply voltage range ESD ratings Operating temperature Storage temperature Breakdown voltage at pin SW and TSS and VOUT Maximum voltage applied on SHDN pin HBM MIL STD 883C Test conditions Value Min. Typ. Max. 2.5 2 - 40 - 65 20 VIN + 85 150 5 Unit V kV C C V V
3/8
STLD20D
Table 4: Electrical Characteristics (for VIN = 2.8 to 4.2V and Tj = 25C) Symbol VIN IOUT ISD IQ SW Parameter Operating Input voltage range Average regulated current IOUT = 20mA Stand-by current Quiescent current consumption Boost switch RDSON RLED = 15 VIN = 4.2V VIN = 4.2V VIN = 2.8V VIN = 4.2V VIN = 2.8V VIN = 4.2V VIN = 2.8V VIN = 4.2V VIN = 2.8V VIN = 4.2V 5.5 4.7 0.43 0.51 Test conditions Value Min. Typ. Max. 2.8 19 20 4.2 21 1 0.6 0.6 Unit V mA A mA
SHDN = low SHDN = high
SOT23-8L Tj = 25C ISW = 250mA QFN Tj = 25C ISW = 250mA
0.45 0.49 0.65 0.55 6.1 5.2 6.2 5.3 0.285 0.300 0.315 V % 85 0.9 mA/V 80
LDS
Load disconnect switch SOT23-8L Tj = 25C RDSON ILDS = 20mA QFN Tj = 25C ILDS = 20mA
FB Line Eff
Feedback voltage Variation of the LED current versus the input voltage: RLED = 15 Efficiency with 4 LEDS Vout = 16V Circuit configuration (figure 1) L: Murata LQH32CN100K33 Diode: BAT20J VIN = 2.8V VIN = 4.2V
Switching frequency DCMIN ILIM OVP HystOV OTP HystOT SHDN Minimum duty cycle Peak current boost switch Overvoltage protection Overvoltage hysteresis Over temperature protection Over temperature protection hysteresis Shutdown signal logic Disable Low Enable high Table 5: Thermal Characteristics Symbol
Rth(j-a)
400
500 22
600 25 640
kHz % mA Vdc Vdc C C
L = 10H RSET = GND (STLD20D-C8) 17.5 18.5 0.7 110 5 VIL VIH 1.2
20
0.3
V
Parameter Mounted on epoxy board without copper heatsink SOT23-8L QFN
Value Min. Typ. Max. 300 350
Unit C/W
4/8
STLD20D
FUNCTIONAL DESCRIPTION 1. BOOST CONTROLLER: The STLD20D is a PWM mode control boost converter operating at 500kHz in discontinuous mode. An automatic compensation of the oscillation ramp allows rejection of the battery voltage transient. The LED constant regulation (referred figure 4 ) is done by sensing the LED current through the resistance RLED (figure 1). The voltage across RLED is used by the feedback loop of the controller (pin FB). Figure 6: LED current versus input voltage
ILED(mA)
21.00 20.80 20.60 20.40 20.20 20.00 19.80 19.60 19.40 19.20 19.00 2.5 3 3.5 4 4.5 5
VIN(V)
2. PEAK INDUCTOR CURRENT LIMITATION AND SOFT START FUNCTION: An integrated current sensor senses the peak drain current of the switch SW in order to keep the inductor current below its saturation level. Since the peak drain current exceeds 590mA (if RSET = GND for STLD20D-C8), the RS flip flop turns off the switch SW. During start up, this peak drain current limitation acts inherently like a soft start function . 3. PEAK INDUCTOR CURRENT ADJUSTABILITY (STLD20D-C8 ONLY) The peak current of the boost inductor should always be below the saturation current. In order to provide flexibility in the selection of the inductor, the maximum peak inductor current can be adjusted by connecting a resistor at the pin RSET. The figure 5 gives the value of the resistance RSET versus the peak inductor current limit ILMAX at 25C. If a low ripple is espected on the battery voltage bus, then the maximum peak inductor current should be reduced. Figure 7: RSET (k) versus ILMAX (A)
RSET(k)
120 VIN=3.2V 100 80 60 40 20 0 0.3 0.4 0.5 ILmax(A) 0.6 0.7 VIN=4.2V
RSET = f(ILmax)
4. SHUTDOWN: The SHDN pin is a low logic input signal and allows turning off the controller without cutting the input voltage from the boost regulator circuit. An integrated LED disconnect switch LDS disconnects the LEDs branch in shutdown mode .This arrangement allows eliminating the DC current path that normally exists with traditional boost regulator in shutdown mode. 5. BRIGHTNESS CONTROL: The brightness of the Led is adjusted by pulsing the shutdown pin with a low frequency PWM signal. By using such a PWM signal the controller is alternatively ON and OFF and the LED current changes from full current to zero. The duty cycle allows to regulate the average LED current . This scheme ensures that when the LEDs are ON they are driven at the full current without risk of color change. 6. OTP: An integrated temperature sensor senses the temperature of the junction of the controller. when this temperature exceeds 110C min fixed internally the controller is automatically turned OFF . When the temperature is reduced the operation of the device automatically recovers.
5/8
STLD20D
7. OVER VOLTAGE PROTECTION (OVP): In case of failure and if the LED branch is cut, then there is no signal at the feedback pin FB (figure 1), the PWM controller will then switches with a maximum duty cycle. This will generate a voltage at the pin SW and VOUT that can exceed the maximum rating of the device. The overvoltage protection bloc senses the output voltage at the pin VOUT (figure 1). If the voltage exceeds 18.5Vdc typical the controller is automatically turned OFF. When the voltage is reduced of 0.7V, the operation of the device automatically recovers. 8. EFFICIENCY (Figure 1 & 2) The efficiency takes into account these following losses: RLED ohmic losses

Boost switch SW losses LED disconnect switch LDS Boost inductor losses Boost diode losses Total driver consumption.
Figure 8: SOT23-8L Package Mechanical Data DIMENSIONS REF.
<
GAUGE PLANE
Millimeters Min. Max. 1.45 0.15 0.90 0.22 0.08 2.80 2.60 1.50 1.30 0.38 0.22 3 3 1.75
Inches Min. Max. 0.057 0.006 0.035 0.008 0.003 0.110 1.102 0.059 0.051 0.015 0.008 0.118 0.118 0.069
A
A2
A1 L
A A1
c
D e1 e
A2 b c D E E1
0.25 SEATING PLANE
E
E1
e e1 L
c b
0.65 typ. 1.95 typ. 0.30 0 0.60 8
0.026 typ. 0.077 typ. 0.012 0 0.024 8
<
6/8
STLD20D
Figure 9: QFN 3x3 8L Package Mechanical Data
L2
REF.
E
D1
L2
A A1 e b
A2 A3
L r L1 k r1 D2
b1
E2
A A1 A2 A3 b b1 D D2 E E2 e K L L1 L2 r r1
DIMENSIONS Millimeters Inches Min. Typ. Max. Min. Typ. 0.80 0.90 1.00 0.031 0.035 0.03 0.03 0.001 0.65 0.70 0.75 0.026 0.028 0.15 0.20 0.25 0.006 0.008 0.29 0.31 0.39 0.011 0.012 0.17 0.30 0.007 3.00 0.118 1.92 2.02 2.12 0.076 0.079 3.00 0.118 1.11 1.21 1.31 0.044 0.048 0.65 0.026 0.20 0.008 0.20 0.29 0.45 0.008 0.011 0.16 0.24 0.40 0.006 0.009 0.13 0.15 0.006 0.15 0.006
Max. 0.039 0.002 0.030 0.010 0.015 0.012 0.083 0.051
0.018 0.016 0.005
Figure 10: QFN Foot Print Dimensions (in millimeters)
0.65 0.41 0.39 0.34 4.00 1.21
2.02 4.00
- Exposed pad is not connected to the ground of the dice. - Connect exposed pad to pin one.
7/8
STLD20D
Table 6: Ordering Information Part Number STLD20D-C8 STLD20D-DEF Marking L2D L2D Package SOT23-8L QFN 3x3 8L Weight 0.2 g 0.22 g Base qty 3000 3000 Delivery mode Tape & reel Tape & reel
Table 7: Revision History Date August-2004 12-Oct-2004 Revision 1 2 First issue Table 4 on page 4 following parameters values updated: . IOUT (min), IQ (min), SW (QFN max), LDS (QFN max), ILIM, HystOT . FB VAR symbol changed to Line and value changed from 0.7 to 0.9 mA/V Description of Changes
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners (c) 2004 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America www.st.com
8/8

▲Up To Search▲

Price & Availability of STLD20D-C8

	To Download STLD20D-C8 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .