STMICROELECTRONICS STLDC08PUR

STLDC08
Step-up controller for LED supply
Features
■
Input voltage range from 0.8 V to 3.6 V
■
Overvoltage protection
■
Drives N-channel MOSFET or NPN bipolar
transistor
■
No control loop compensation required
■
FET driver for very precise PWM dimming
DFN10 (3 x 3 mm)
Applications
■
Single/dual cell NiMH, NiCd, or alkaline
batteries
■
Small appliances LED lighting
■
Portable lighting
Description
The STLDC08 LED driver step-up controller is
optimized to operate from one or two NiCd/NiMH
or alkaline cells. The IC is able to drive an
external MOSFET (N-channel) enabling it for use
with wide power levels. Hysteretic control
eliminates the need for small signal control loop
compensation. The IC integrates an FET driver for
a precise PWM dimming. STLDC08 comes in a
DFN10 (3 x 3 mm) package.
Table 1.
Device summary
Order code
Marking
Package
STLDC08PUR
STLDC08
DFN10 (3 x 3 mm.)
February 2011
Doc ID 18476 Rev 1
1/29
www.st.com
29
Contents
STLDC08
Contents
1
Application diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2
Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3
Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5
Typical performance characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6
Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7
Detailed description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8
7.1
Main control loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.2
Start up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.3
Over voltage protection (OVP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.4
Enable/PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.5
Dimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1
LED current programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.2
Duty cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.3
Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.4
Inductor peak current limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.5
Power MOSFET selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.6
Schottky diode selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.7
Input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.8
Output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9
Demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
10
Layout suggestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
11
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2/29
Doc ID 18476 Rev 1
STLDC08
12
Contents
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Doc ID 18476 Rev 1
3/29
Application diagram
STLDC08
1
Application diagram
Figure 1.
Electric schematic optimized for 2 LEDs and ILED = 200 mA
L1
D1
RF
BATTERY
C1
C2
D3
M1
C3
Rs
U1
4
7
EN/PWM
3
VCC
DRV
EN/PWM
SENSE
VOUT
2VCC
PWMOUT
C4
10
V5
FB
GND
EXP
8
11
C5
D2
9
6
C6
1
M2
2
5
Rfb
AM07845v1
Table 2.
List of components
Reference
Manufacturer
Part number
Value
Size
C1
Murata
GRM21BR60J475
4.7 µF, 6.3 V
0805
C2
Murata
GRM31CB31C106K
10 µF, 16 V
1206
C4
Murata
GRM188R70J103KA01B
10 nF, 6.3 V
0603
C3, C5, C6
Murata
GRM188R61C105K
1 µF, 16 V
0603
L
Coilcraft
LPS6235-103ML
10 µH
6 mm x 6 mm
M1,M2
STMicroelectronics
STS5DNF20V
SO-8
D1
STMicroelectronics
STPS2L30
SMA
4/29
Rfb
0.47 Ω
0805
Rs
0.047 Ω
0805
RF
0Ω
0603
Doc ID 18476 Rev 1
STLDC08
Application diagram
Figure 2.
Electric schematic optimized for 4 LEDs and ILED = 300 mA
L1
D1
RF
BATTERY
C1
C2
D4
D5
D2
D3
M1
C3
Rs
U1
4
7
EN/PWM
3
VCC
DRV
EN/PWM
SENSE
VOUT
2VCC
PWMOUT
C4
10
V5
FB
GND
C5
8
9
6
C6
1
2
M2
5
EXP
11
Rfb
AM07892v1
Table 3.
List of components
Part reference
Manufacturer
Part number
Value
Size
C1
Murata
GRM21BR60J106KE19
10 µF, 6.3 V
0805
C2
Murata
GRM31CR61C226K
22 µF, 16 V
1206
C4
Murata
GRM188R70J103KA01B
10 nF, 6.3 V
0603
C3, C5, C6
Murata
GRM188R61C105K
1 µF, 16 V
0603
M1,M2
STMicroelectronics
STS5DNF20V
SO-8
D1
STMicroelectronics
STPS2L30
SMA
L
Coilcraft
DO3316P-223_L
22 µH
12.95 mm x 9.4 mm
Rfb
0.33 Ω
0805
Rs
0.033 Ω
0805
RF
0Ω
0603
Doc ID 18476 Rev 1
5/29
Absolute maximum ratings
STLDC08
2
Absolute maximum ratings
Table 4.
Absolute maximum ratings
Symbol
Parameter
VCC
Supply voltage
Value
Unit
- 0.3 to 4.6
V
EN/PWM
Analog input
- 0.3 to 7
V
FB
Analog input
- 0.3 to 2
V
SENSE
Analog input
- 0.3 to 20
V
2VCC
Analog outputs
0 to 4
V
V5
Analog outputs
- 0.3 to 7
V
DRV, PWMOUT
Analog outputs
VCC - 1.2 to 7
V
VOUT
Output voltage
- 0.3 to 20
V
ESD
Human body model (all pins)
±2
kV
PD
DFN10L 3x3 TA = 25 °C
2.2
W
TJ
Junction temperature
- 40 to 85
°C
Storage temperature range
- 55 to 85
°C
TSTG
Note:
Absolute maximum ratings are those values beyond which damage to the device may occur.
Functional operation under these conditions is not implied.
Table 5.
Thermal data
Symbol
RthJC
RthJA
Parameter
Thermal resistance junction-case
Thermal resistance junction-ambient
1. With two sides, two planes PCB following EIA/JEDEC JESD51-7 standard.
6/29
Doc ID 18476 Rev 1
Value
Unit
3
°C/W
57.1
(1)
°C/W
STLDC08
Pin configuration
3
Pin configuration
Figure 3.
Pin connections (top through view)
Bottom view
Table 6.
Top view
Pin description
Pin #
Pin name
1
VOUT
2
PWMOUT
3
2Vcc
Charge pump output
4
VCC
Supply voltage when VOUT < 2 V, this pin represents the input of the internal charge
pump
5
FB
6
SENSE
7
EN/PWM
8
GND
Ground reference
9
DRV
Driver output for Boost stage MOSFET
10
V5
Exposed Pad
Pin function
Over voltage protection and supply pin for the IC when VOUT > 2 V
Driver of the external MOSFET for PWM dimming. The driver stage is controlled by
EN/PWM signal
Feedback pin for LED current control
Sense resistor for current mode control and peak current limit
Enable pin and PWM control input for PWMOUT pin
Internal regulator output. Decouple this pin locally to the IC ground with a minimum
of 1 µF ceramic capacitor
The exposed pad needs to be connected and soldered to analog ground
Doc ID 18476 Rev 1
7/29
Electrical characteristics
4
STLDC08
Electrical characteristics
TA = -40 to 85; CIN = 22 µF; COUT =10 µF; PWMOUT = 3300 pF; DVR = 3300 pF; 2VCC =10
nF; V5 =1 µF; VCC = 1.5V; VOUT = 3 V; FB = GND; SENSE = GND; EN/PWM = VCC; unless
otherwise specified.
Table 7.
Electrical characteristics
Symbol
Parameter
Test conditions
Min.
Typ.
Max.
Unit
3.6
V
General section
VCC
IVCC
OVP
IVOUT
2VCC
Supply voltage range
VOUT = GND
0.8
Supply current measured on VCC
VOUT = GND
pin with charge pump ON
3
Shutdown current
EN = GND Shutdown mode
5
Overvoltage protection
Rising edge
Operating supply current
measured on VOUT pin
18
mA
10
µA
19.5
V
100
µA
VOUT = 3 V, FB = 500 mV (no
switching)
60
VOUT = 3 V, FB = GND
(switching)
800
VOUT = 10 V, FB = GND
(switching)
1.3
2
mA
5
10
µA
Shutdown current
EN = GND
Charge pump ON
VOUT floating; VCC = 0.8 V
1.5
µA
V
Driver section (DRV output)
VDRVL
Low level voltage
IDRV = 100 mA
80
160
mV
VDRVH
High level voltage
IDRV = -100 mA
120
240
mV
tR
Rise time
CDRV = 3300 pF
30
ns
tF
Fall time
CDRV = 3300 pF
20
ns
VFB
Feedback voltage
TA = 25 °C
IFB
Bias current
FB = 2 V
FB
90
105
116
mV
20
500
nA
Timing
TOFF(MIN)
Minimum Off time
1
µs
TON(MAX)
Maximum On time
20
µs
PWM OUT section
VPWMOUTL Low level voltage
IPWMOUT = 100 mA
200
400
mV
VPWMOUTH High level voltage
IPWMOUT = - 100 mA
250
500
mV
8/29
tr
Rise time
CPWMOUT = 3300 pF
30
ns
tf
Fall time
CPWMOUT = 3300 pF
20
ns
Doc ID 18476 Rev 1
STLDC08
Table 7.
Electrical characteristics
Electrical characteristics (continued)
Symbol
Parameter
Test conditions
Min.
Typ.
Max.
Unit
70
100
130
mV
10
20
µA
SENSE
VSENSE MAX
ISENSE
Maximum current sense
threshold
Bias current
VSENSE = 20 V
EN/PWM section
VIL
Low level threshold
VCC = 0.8 V
0.3
V
VIL
Low level threshold
VCC = 3.6 V
0.4
V
VIH
High level threshold
VCC = 0.8 V
0.8
V
VIH
High level threshold
VCC = 3.6 V
1.2
V
IEN/PWM
EN/PWM pin current
EN/PWM = 3.6 V
2
µA
IEN/PWM
EN/PWM pin current
EN/PWM = 5 V
5
µA
+ 5 V regulator
V5
Output voltage
ΔV5/ΔVOUT Line regulation
ΔV5
Load regulation
VDROPOUT Dropout voltage
ICC
Short circuit current
VOUT = 6 V; I5 = 10 mA
4.8
6 V < VOUT < 18 V; I5 = 10 mA
5
5.2
V
0.02
%/V
0.01
%/mA
I5 = 10 mA
20
mV
VOUT = 18 V; V5 = 0 V
140
mA
0 < I5 < 10 mA VOUT = 18 V
Doc ID 18476 Rev 1
0.02
9/29
Typical performance characteristics
STLDC08
5
Typical performance characteristics
Figure 4.
VFB vs. temperature
Figure 5.
!-V
Maximum VSENSE vs. temperature
!-V
63%.3% ;M6=
6&" ;M6=
6 /54 6
6 /54 6
Figure 6.
IOUT vs. temperature FB = 0.5 V
Figure 7.
!-V
IOUT vs. temperature FB = GND
!-V
) 6/54 ;M!=
)6/54 ;—!=
6 /54 6&"6
6 /54 6&"'.$
Figure 8.
4EMPERATURE; #=
4EMPERATURE; #=
Efficiency vs. input voltage 2 LEDs Figure 9.
!-V
Efficiency vs. input voltage 4 LEDs
!-V
%FF ;=
%FF ;=
),%$ M!,%$S
),%$ M!,%$S
6## ;6=
10/29
4EMPERATURE; #=
4EMPERATURE ; #=
6## ;6=
Doc ID 18476 Rev 1
STLDC08
Typical performance characteristics
Figure 10. Startup timing and dimming ILED
vs. time, 2 LEDs
Figure 11. Dimming EN/PWM = 200 Hz, 2 LEDs
VCC = 1.5 V; ILED = 200 mA 2LEDs
VCC = 1.5 V; ILED = 200 mA 2LEDs
Figure 12. Startup timing and dimming ILED
vs. time, 4 LEDs
Figure 13. Dimming EN/PWM = 200 Hz, 4 LEDs
VCC = 3.6 V; ILED = 300 mA 4LEDs
VCC = 3.6 V; ILED = 300 mA 4LEDs
Figure 14. VCC = 1.5 V; ILED = 200 mA, 2LEDs
Figure 15. VCC = 3.6 V; ILED = 300 mA, 4LEDs
Doc ID 18476 Rev 1
11/29
Block diagram
6
STLDC08
Block diagram
Figure 16. Block diagram
VOUT
Vcc
Over Voltage
Protection
+
-
VOUT
OVP TH
+5 V
LDO
Charge
Pump
+5 V
2Vcc
2Vcc
TOFF timer
TOFF = 1 µsec
S
DRV
DRIVER
Q
R
GND
TONMAX = 20 µsec
Peak Current
Comparator
SENSE
+
OCP
-
RESET
OCP_TH
Sensed
Current Ramp
OCP_TH
Peak Current
Control
FB
-
FB
Feedback
+
100 mV
Comparator
EN/PWM
PWMOUT
DRIVER
AM07846v1
12/29
Doc ID 18476 Rev 1
STLDC08
Detailed description
7
Detailed description
7.1
Main control loop
The STLDC08 is an LED driver step-up controller dedicated to handheld equipment, having
a typical voltage ranging from 0.8 V to 1.5 V. The controller drives an N-channel Power
MOSFET and implements a hysteretic current mode control with constant OFF time.
Hysteretic operation eliminates the need for small signal control loop compensation. The
control loop adapts the value of the inductor peak current as needed to deliver the desired
current on the LED branch. The LED current is set by an external sense resistor RFB
inserted between the feedback pin (FB) and GND. When the current mode control system
operates in continuous mode the control peak current is almost equivalent to the average
current control.
7.2
Start up
At the startup phase, when the device is connected to the battery or when the EN pin is
pulled high, the internal 2x charge pump starts to work, boosting the voltage on the 2VCC
pin. When the 2VCC pin reaches 1.7 V a soft-start cycle begins. The external main MOSFET
is switched on/off allowing the charging of the output capacitor.
If the optional PWMOUT MOSFET is used for the dimming operation, the PWMOUT pin is
held low, further assuring that no current is flowing. The PWMOUT pin starts to follow the
PWM input when the soft-start cycle is ended.
When VOUT voltage exceeds 1.9 V, the chip starts drawing its supply current from VOUT
rather than from VCC, the charge pump is turned off and the voltage on the 2VCC pin goes to
zero. When VOUT exceeds the forward voltage of LED VLED, the current starts flowing trough
the LED, but, at this point, the voltage on the DRV pin is high enough to allow the main
MOSFET to carry the necessary current.
Doc ID 18476 Rev 1
13/29
Detailed description
STLDC08
Figure 17. Timing diagram
VCC
1.7 V
2VCC
1.9 V
VOUT
DRV
VOUT >1.9 V STLDC08 is
supplied by VOUT
ICC
VOUT > VLED, the current starts
flowing through the LEDs
ILED
Follows EN/PWM
input
Soft start cycle ended,
PWMOUT is realeased
PWMOUT
Charge Pump
active
7.3
STLDC08 supplied by
VOUT
AM07847v1
Over voltage protection (OVP)
As with any current source, the output voltage rises when the output gets high impedance or
is disconnected. To prevent the output voltage exceeding the maximum switch voltage rating
of the main switch, an overvoltage protection circuit is integrated. As soon as the output
voltage exceeds the OVP threshold, the converter stops switching and the output voltage
drops. When the output voltage falls below the OVP threshold, the converter continues
operation until the output voltage exceeds the OVP threshold again.
7.4
Enable/PWM
The enable pin allows disabling and enabling of the device as well as brightness control of
the LEDs by applying a PWM signal. In order to avoid visible flicker, the frequency of the
PWM signal should be higher than 120 Hz. Changing the PWM duty cycle therefore
changes the LED brightness.
14/29
Doc ID 18476 Rev 1
STLDC08
7.5
Detailed description
Dimming
When PWMOUT goes to zero, the LED current immediately goes to zero and the energy
stored in the coil is discharged on the output capacitor, causing an increase in the output
voltage. As soon as the PWM goes back to high value, there is a big spike current on the
LED. This could damage the LED itself. To avoid this, as soon as the input PWM signal goes
to zero the controller immediately turns off the main switch (in order to discharge the coil
current on the LED branch). In this way the PWM power is turned off with a delay in order to
guarantee that FB goes high after PowerMOS turn off. After this delay, the flip-flop is ready
to be set and the PWM power is turned off. In this condition the output voltage is slightly
lower than the regulated value, but a current spike on the LED is avoided.
Doc ID 18476 Rev 1
15/29
Application information
STLDC08
8
Application information
8.1
LED current programming
The LED current is set by an external resistor connected between the FB pin and GND. The
following equation can be used to calculate the value of the RFB resistor which guarantees
the desired output current:
Equation 1
RFB =
0.1
ILED
The feedback signal VFB is compared with the internal precision 100 mV voltage reference
by the error amplifier. The internal reference has a guaranteed tolerance of 10 %. Tolerance
of the sense resistor adds additional error to the output voltage. 1 % resistors are
recommended.
8.2
Duty cycle
The controlled off-time architecture is a hysteretic mode control. Hysteretic operation
eliminates the need for small signal control loop compensation. When the converter runs in
continuous conduction mode (CCM) the controller adapts the TON time in order to obtain the
duty cycle given by the following relationship:
Equation 2
D = 1−
VIN
VOUT + VD
where VO is the output voltage given by:
Equation 3
VO = n × VF(LED) + VFB
and VD is the forward voltage of the Schottky diode.
8.3
Inductor selection
As the hysteretic control scheme is inherently stable, the inductor value does not affect the
stability of the regulator. The switching frequency, peak inductor current, and allowable
ripple of the output current determine the value of the inductor.
LED manufacturers generally recommend a value for LED current ripple ranging from 5 % to
20 % of LED average current.
16/29
Doc ID 18476 Rev 1
STLDC08
Application information
As a first approximation we choose the inductor ripple current, IL, equal to approximately 40
% of the output current. Higher ripple current allows for smaller inductors, but it also
increases the output capacitance for a given LED current ripple requirement. Conversely,
lower ripple current can be obtained increasing the value of the inductance, and this enables
a reduction of the output capacitor value. This trade-off can be altered once standard
inductance and capacitance values are chosen.
IL is determined by the input and output voltage, the value of the inductance, and TOFF.
Figure 18. Timing diagram
IPEAK
IL
IRIPPLE
I
IIN = OUT
1− D
IOUT
t
TON
TOFF
AM07848v1
The minimum value of inductance which guarantees the fixed inductor ripple current can be
determined using the following equation:
Equation 4
L>
(VOUT + Vd - VINMIN )
× TOFF
(ΔIL )
where Vd is the forward drop of the Schottky diode, IL is the fixed inductor ripple current, and
TOFF is the constant OFF time.
The following equation shows the average inductor current as a function of the output
current and duty cycle.
Equation 5
I
IL( AVG) = LED
1− D
An inductor that can carry the maximum input DC current which occurs at the minimum
input voltage should be chosen. The peak-to-peak ripple current is set by the inductance
and a good starting point is to choose a ripple current of at least 40 % of its maximum value
of the:
Doc ID 18476 Rev 1
17/29
Application information
STLDC08
Equation 6
ΔIL = 40% × IL( AVG) = 40% ×
ILED
1 − DMAX
Where DMAX is given by:
Equation 7
DMAX = 1 −
VIN(MIN)
VOUT + VD
The value of the peak current on the inductor is given by the following equation:
Equation 8
IL(PK ) = IL( AVG) +
ΔIL
2
The minimum required saturation current of the inductor must be greater than IL(PK) and can
be expressed as follows:
Equation 9
IL(SAT ) > IL(PK ) =
IOUT
ΔI
+ L
1 − DMAX
2
The saturation current rating for the inductor should be checked at the maximum duty cycle
and maximum output current.
8.4
Inductor peak current limit
The value of the inductor peak current limit can be programmed either by using a sense
resistor or by using the RDSON of the main Power MOSFET.
The following equation gives the relationship between the peak current limit and the value of
the sense resistor:
Equation 10
IIN(MAX) =
VSENSE
0.1
=
RSENSE RSENSE
The sense resistor value can be determined fixing the value of the inductor peak current
limit equal to twice the value of the inductor peak current in steady-state conditions.
18/29
Doc ID 18476 Rev 1
STLDC08
Application information
Equation 11
IIN(MAX) = 2 × IL(PK )
Equation 12
IL(PK ) =
ΔI
ILED
+ L
1 − DMAX
2
Equation 13
RSENSE =
0.1
2 × IL(PK )
If the RDS (ON) of the main Power MOSFET is used to sense the current on the inductor the
following procedure must be performed to choose the Power MOSFET. During ON time, the
SENSE comparator limits the voltage across the Power MOSFET to a nominal 100 mV. In
that case, the maximum inductor current is given by the following relationships:
Equation 14
IL(MAX) =
VSENSE
100mV
=
RDS(ON) RDS(ON)
Equation 15
IL(MAX) = 2 × IL(PK ) = 2 ×
ILED
ΔI ⎞
⎛
× ⎜1 + L ⎟⎟
1 − DMAX ⎜⎝
2 ⎠
Equation 16
RDS(ON) < 0.1×
8.5
1 − DMAX
ΔI ⎞
⎛
2 × ILED × ⎜1 + L ⎟
2 ⎠
⎝
Power MOSFET selection
A key parameter to take into account in the selection of the N-MOSFET is the maximum
continuous drain current. As a safety design, it is important to choose a maximum
continuous drain current equal to twice the maximum input current.
Doc ID 18476 Rev 1
19/29
Application information
STLDC08
Figure 19. Current diagram ON state
L1
VBAT
LX
D1
COUT
CIN
LED
DVR
SENSE
Rsense
STLDC08
VOUT
FB
ON state
RFB
AM07849v1
Figure 20. Current diagram OFF state
LX
L1
VBAT
D1
CIN
COUT
LED
DVR
SENSE
Rsense
STLDC08
VOUT
FB
OFF state
RFB
AM07850v1
Another important parameter is the drain source breakdown voltage. During the ON state,
the potential of the LX point is 0 V, while during the OFF state the potential of this point rises
to the output voltage plus the forward voltage of the D1. Therefore, the absolute VDS rating
of the main switch must be greater than this voltage to prevent main switch damage.
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STLDC08
8.6
Application information
Schottky diode selection
Schottky diodes, with their low forward voltage and fast recovery time, are the ideal choice to
maximize efficiency. The output diode in a boost converter conducts current only when the
power switch is OFF. The average current is equal to the output current and the peak current
is equal to the peak inductor current. Ensure that the diode's average and peak current
ratings exceed the average and peak inductor current, respectively. In addition, the diode's
reverse breakdown voltage must exceed the regulator output voltage.
8.7
Input capacitor
The input capacitor of a boost converter is less critical than the output capacitor, due to the
fact that the input current waveform is continuous. The input voltage source impedance
determines the size of the input capacitor, which is typically in the range of 10 µF to 100 µF.
A low ESR capacitor is recommended though it is not as critical as the output capacitor.
8.8
Output capacitor
For best output voltage filtering, a low ESR output capacitor is recommended. Ceramic
capacitors have a low ESR value but tantalum capacitors can be used as well, depending on
the application.
The output voltage ripple consists of two parts, the first is the product IL(PK) ESR, the second
is caused by the charging and discharging process of the output capacitor.
Equation 17
ΔVOUT =
TON × ILED
+ ESR × IL(PK )
COUT
where:
IL(PK) = Peak current
ILED = Load current
COUT = Selected output capacitor
ESR = Output capacitor ESR value
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Demonstration board
9
STLDC08
Demonstration board
Figure 21. Electrical schematic
TP1
VIN
J1
TP2
SW
L1
1
TP3
VOUT
D1
1
J3
1
1
2
1
2
RF
POWER IN
C1
TP5
LED
C2
1
J2
TP4
1
2
DRV
C3
M1
1
SENSE
GND
Rs
U1
J4
4
1
2
3
7
3
EN/PWM
VCC
DRV
EN/PWM
SENSE
VOUT
2VCC
PWMOUT
C4
10
V5
C5
GND
8
EXP
FB
9
6
C6
1
2
M2
5
11
Rfb
AM07900v1
Table 8.
Bill of material optimized for 2 LEDs and ILED = 200 mA
Reference
Manufacturer
Part number
Value
Size
C1
Murata
GRM21BR60J475
4.7 µF 6.3V
0805
C2
Murata
GRM31CB31C106K
10 µF 16 V
1206
C4
Murata
GRM188R70J103KA01B
10 nF, 6.3 V
0603
C3, C5, C6
Murata
GRM188R61C105K
1 µF, 16 V
0603
L
Coilcraft
LPS6235-103ML
10µH
6 mm x 6 mm
M1,M2
STMicroelectronics
STS5DNF20V
SO-8
D1
STMicroelectronics
STPS2L30
SMA
22/29
Rfb
0.47 Ω
0805
Rs
0.047 Ω
0805
RF
0Ω
Doc ID 18476 Rev 1
STLDC08
10
Layout suggestion
Layout suggestion
Figure 22. Assembly layer
Figure 23. Top layer
Doc ID 18476 Rev 1
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Layout suggestion
STLDC08
Figure 24. Bottom layer
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STLDC08
11
Package mechanical data
Package mechanical data
In order to meet environmental requirements, ST offers these devices in different grades of
ECOPACK® packages, depending on their level of environmental compliance. ECOPACK®
specifications, grade definitions and product status are available at: www.st.com.
ECOPACK® is an ST trademark.
Doc ID 18476 Rev 1
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Package mechanical data
STLDC08
DFN10 (3x3 mm) mechanical data
mm.
mils.
Dim.
A
Min.
Typ.
Max.
Min.
Typ.
Max.
0.80
0.90
1.00
31.5
35.4
39.4
0.02
0.05
0.8
2.0
0.65
0.80
25.6
31.5
A1
A2
0.55
A3
21.7
0.20
7.9
b
0.18
0.25
0.30
7.1
9.8
11.8
D
2.85
3.00
3.15
112.2
118.1
124.0
D2
2.20
E
2.85
118.1
124.0
E2
1.40
e
L
ddd
86.6
3.00
3.15
112.2
1.75
55.1
0.50
0.30
0.40
68.9
19.7
0.50
0.08
11.8
15.7
19.7
3.1
7426335F
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Doc ID 18476 Rev 1
STLDC08
Package mechanical data
Tape & reel QFNxx/DFNxx (3x3) mechanical data
mm.
inch.
Dim.
Min.
Typ.
A
Max.
Min.
Typ.
180
13.2
7.087
C
12.8
D
20.2
0.795
N
60
2.362
T
0.504
0.519
14.4
0.567
Ao
3.3
0.130
Bo
3.3
0.130
Ko
1.1
0.043
Po
4
0.157
P
8
0.315
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Max.
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Revision history
STLDC08
12
Revision history
Table 9.
Document revision history
Date
Revision
22-Feb-2011
1
28/29
Changes
First release.
Doc ID 18476 Rev 1
STLDC08
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