STMICROELECTRONICS STLD20D-C8

STLD20D
®
WHITE LED POWER SUPPLY
ASD™
PRELIMINARY DATA
FEATURES
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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 < 1µA
Small external inductor (10µH, height < 2mm)
Tiny ceramic external capacitor
Can be supplied by a Li-ion battery - VIN range:
2.5Vdc to 5Vdc
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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=25°C)
Figure 1: Basic connection
Efficiency (%)
88
D
L = 10µH
VBATT
87
86
Cin = 2.2µF
85
Cout = 1µF
84
VOUT
SW
83
RSET (*)
82
ILED = 20mA
RSET
VIN
STLD20D
81
LDS
80
FB
79
SHDN
RLED
GND
78
2.5
D: STM BAT20J
L: Murata LQH32CN100K33
(*) STLD20D-C8 only
3
3.5
4
4.5
5
Input voltage (Vdc)
Table 1: Order Codes
Part Number
STLD20D-C8
STLD20D-DEF
October 2004
Marking
L2D
L2D
Package
SOT23-8L
QFN 3x3 8L
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)
SHDN
LDS
RSET
FB
GND
VIN
VIN
VOUT
3
4
SHDN RSET
SW
EXPOSED PAD
VIN
2
GND
SW
GND
1
Figure 4: STLD20D-DEF Pin-Out Designation
(QFN 8L top view)
SHDN
N/C
VOUT
LDS
FB
5
6
7
8
1
2
3
4
5
6
7
8
FB
LDS
VOUT
SW
GND
VIN
SHDN
N/C
FB
LDS
VOUT
SW
Figure 5: Block Diagram
SW
OTP
OSCILLATOR
VIN
OVP
RAMP
OSCILLATOR
COMPENSATION
VOUT
POWER
FAULT
ENABLE
VIN
S
+
-
SW
Q
R
PWN
COMP.
SHDN
+
-
T°
VIN
DRAIN
CURRENT
REFERENCE
RSET (*)
LED DISCONNECT
LDS
VIN
SHDN
LDS
FB
+
LED CURRENT
REFERENCE
GND
(*) STLD20D-C8 only
2/8
STLD20D
Table 2: External Components Pproposal (note 1) - Referred basic connection (figure 1)
Symbol
Parameter
RLED
LED current resistance
CIN
Input filtering capacitor
COUT
L
Test Conditions
Value
Min. Typ. Max.
Ceramic type
Output capacitance
Boost inductor (height < 2mm)
15
Ω
2.2
µF
1
Inductance
10
Resistance at 500kHz
D
Boost diode
(STMicroelectronics BAT20J type)
Unit
µH
1
Ω
Isat (RSET = 100kΩ)
300
mA
VRRM
23
Vdc
IF (peak forward current)
1
A
VF @ IF = 0.1A Tj = 25°C
0.35
0.4
V
IR @ Tj = 25°C VR = 15V
3
12
µA
IR @ Tj = 85°C VR = 15V
120
250
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
Parameter
Test conditions
Supply voltage range
Value
Min. Typ. Max.
2.5
5
Unit
V
VESD
ESD ratings
TOP
Operating temperature
- 40
+ 85
°C
Tstg
Storage temperature
- 65
150
°C
HBM MIL STD 883C
BVDS
Breakdown voltage at pin SW and TSS and VOUT
SHDN
Maximum voltage applied on SHDN pin
2
kV
20
V
VIN
V
3/8
STLD20D
Table 4: Electrical Characteristics (for VIN = 2.8 to 4.2V and Tj = 25°C)
Symbol
Parameter
Test conditions
VIN
Operating Input voltage range
IOUT
Average regulated current IOUT = 20mA
ISD
Stand-by current
SHDN = low
VIN = 4.2V
IQ
Quiescent current consumption
SHDN = high
VIN = 4.2V
SW
LDS
Boost switch RDSON
Line
Eff
2.8
RLED = 15Ω
19
V
21
mA
1
µA
0.43
0.6
mA
0.6
Ω
20
0.51
VIN = 4.2V
0.45 0.49
QFN
Tj = 25°C
ISW = 250mA
VIN = 2.8V
0.65
VIN = 4.2V
0.55
Load disconnect switch SOT23-8L Tj = 25°C
RDSON
ILDS = 20mA
VIN = 2.8V
5.5
6.1
VIN = 4.2V
4.7
5.2
Tj = 25°C
ILDS = 20mA
VIN = 2.8V
6.2
VIN = 4.2V
5.3
Feedback voltage
0.285 0.300 0.315
Variation of the LED current versus the input voltage: RLED = 15Ω
Efficiency with 4 LEDS
Vout = 16V
Circuit configuration (figure 1)
L: Murata
LQH32CN100K33
Diode: BAT20J
VIN = 2.8V
80
VIN = 4.2V
Minimum duty cycle
%
500
600
kHz
22
25
%
640
mA
20
Vdc
Peak current boost switch
L = 10µH
RSET = GND (STLD20D-C8)
OVP
Overvoltage protection
17.5 18.5
HystOV
Overvoltage hysteresis
0.7
Vdc
110
HystOT
Over temperature protection hysteresis
SHDN
Shutdown signal logic
°C
5
Disable Low
VIL
Enable high
VIH
V
85
400
Over temperature protection
Ω
0.9 mA/V
ILIM
OTP
Unit
4.2
VIN = 2.8V
Switching
frequency
DCMIN
Min. Typ. Max.
SOT23-8L Tj = 25°C
ISW = 250mA
QFN
FB
Value
°C
0.3
V
1.2
Table 5: Thermal Characteristics
Symbol
Rth(j-a)
4/8
Parameter
Mounted on epoxy board without
copper heatsink
Value
Min.
Typ. Max.
SOT23-8L
300
QFN
350
Unit
°C/W
STLD20D
FUNCTIONAL DESCRIPTION
Figure 6: LED current versus input voltage
ILED(mA)
21.00
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).
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 25°C. If a low ripple is espected on the battery voltage bus, then the
maximum peak inductor current should be reduced.
Figure 7: RSET (kΩ) versus ILMAX (A)
RSET(kΩ)
RSET = f(ILmax)
120
VIN=3.2V
100
VIN=4.2V
80
60
40
20
0
0.3
0.4
0.5
ILmax(A)
0.6
0.7
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 110°C 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
■
■
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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.
<
Min.
GAUGE PLANE
A1
L
D
e1
c
e
0.25
SEATING PLANE
c
Inches
Max.
Min.
Max.
A
1.45
0.057
A1
0.15
0.006
A2
0.90
1.30
0.035
0.051
b
0.22
0.38
0.008
0.015
c
0.08
0.22
0.003
0.008
D
2.80
3
0.110
0.118
E
2.60
3
1.102
0.118
E1
1.50
1.75
0.059
0.069
E1
E
6/8
Millimeters
A2
A
b
e
0.65 typ.
0.026 typ.
e1
1.95 typ.
0.077 typ.
L
0.30
0.60
0.012
0.024
<
0°
8°
0°
8°
STLD20D
Figure 9: QFN 3x3 8L Package Mechanical Data
REF.
L2
E
L2
D1
A2
A
A3
A1
b
e
L
r
b1
E2
L1
k
r1
D2
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
Marking
Package
Weight
Base qty
STLD20D-C8
STLD20D-DEF
L2D
L2D
SOT23-8L
QFN 3x3 8L
0.2 g
0.22 g
3000
3000
Delivery
mode
Tape & reel
Tape & reel
Table 7: Revision History
Date
Revision
Description of Changes
August-2004
1
First issue
12-Oct-2004
2
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
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.
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All other names are the property of their respective owners
© 2004 STMicroelectronics - All rights reserved
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