AN3115
Application note
LNB power supply based on the LNBH23L
supply and control IC with step-up and I²C interface
Introduction
This application note is intended to provide additional information and suggestions for the
correct use of the LNBH23L device. All waveforms shown are based on the demonstration
board order code STEVAL-CBL007V1 described in Section 3.
The LNBH23L is an integrated solution for supplying/interfacing satellite LNB modules. It
gives good performance in a simple and cheap way, with minimum external components
necessary. It includes all functions needed for LNB supplying and interfacing, in accordance
with international standards. Moreover, it includes an I²C bus interface and, thanks to a fully
integrated step-up DC-DC converter, it functions with a single input voltage supply ranging
from 8 V to 15 V.
Figure 1.
LNBH23L internal block diagram
ISEL
TTX
ADDR SDA
SCL
Vcc
LX
P-GND
-
PWM
Controller
Rsense
Preregulator
+U.V.lockout
+P.ON reset
EN
VSEL
VSEL
TTX
VOUT Control
Vup
Linear Post-reg
-reg
+Protections
+Diagnostics
VoRX
EXTM
TTX
EN
I² C interface
TEN
I²C OLF and OTF
Diagnostics
FB
VoTX
Byp Vcc-- L
22KHz
Oscill.
Pull Down
PDC
Controller
DSQIN
LNBH23L
A-GND
January 2011
Doc ID 16830 Rev 3
1/28
www.st.com
Contents
AN3115
Contents
1
Block diagram and pin function description . . . . . . . . . . . . . . . . . . . . . 5
1.1
Step-up controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2
Pre-regulator block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3
I²C interface and diagnostic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3.1
2
3
Reserved I²C address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4
DiSEqC™ 1.X implementation through EXTM pin . . . . . . . . . . . . . . . . . . . 6
1.5
DiSEqC 1.X Implementation through VoTX and EXTM . . . . . . . . . . . . . . . 7
1.6
PDC optional circuit for DiSEqC 1.X applications using VoTX signal on to
EXTM pin and 22 kHz tone controlled by DSQIN pin 7
1.7
22 kHz oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.8
DiSEqC communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.9
Linear post-regulator, modulator and protection . . . . . . . . . . . . . . . . . . . . 8
1.10
Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Component selection guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1
DC-DC converter inductor (L1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2
Output current limit selection (R2-RSEL) . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.3
DC-DC converter schottky diode (D1) . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4
TVS diode (D6) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.5
DC-DC output capacitors (C3, C4, C6) and ferrite bead . . . . . . . . . . . . . 17
2.6
Input capacitors (C1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.7
PDC optional external circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.8
EXTM-VOTX resistor (R9) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.9
Undervoltage protection diode (D2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Layout guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.1
PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.2
PCB Thermal managing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4
Startup procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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Doc ID 16830 Rev 3
AN3115
List of tables
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
Table 9.
LNBH23L I²C addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
LNBH23L other I²C addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Output load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
LNBH23L pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
LNBH23L demo-board BOM list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Recommended Inductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Recommended Schottky diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Recommended LNBTVS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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3/28
List of figures
AN3115
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
4/28
LNBH23L internal block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
EXTM example of use with 22 kHz IC controller. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
DiSEqC 1.X tone burst with 22 kHz IC controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
DiSEqC timing control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
LNBH23L pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
LNBH23L typical application circuit with internal tone generator . . . . . . . . . . . . . . . . . . . . 11
Typical output current limiting vs. RSEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Example of LNBTVS diode connection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
DC-DC converter output stage with ferrite bead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Application circuit with PDC optional solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
PDC optional circuit load calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
PDC circuit waveform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Tone amplitude vs. R9 value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
PBC top layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
PBC bottom layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
PCB components layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Typical junction to ambient thermal resistance with dual layer PCB, 1oz, 9 thermal vias . 24
PCB connector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Doc ID 16830 Rev 3
AN3115
1
Block diagram and pin function description
Block diagram and pin function description
The internal blocks of the LNBH23L are described in the following paragraphs:
1.1
Step-up controller
The LNBH23L features a built-in step-up DC-DC converter that, from a single supply source
ranging from 8 V to 15 V, generates the voltages that allow the linear post-regulator to work
with minimum power dissipation. The external components of the DC-DC converter are
connected to the LX and VUP pins (see Figure 6). No external power MOSFET is needed.
1.2
Pre-regulator block
This block includes a voltage reference connected to the BYP pin, an undervoltage lockout
circuit, intended to disable the whole circuit when the supplied VCC drops below a fixed
threshold (6.7 V typ), and a power-on reset that sets all the I²C registers to zero when the
VCC is turned on and rises from zero above the “on” threshold (7.3 V typ).
1.3
I²C interface and diagnostic
The main functions of the device are controlled via the I²C bus by writing 5 bits on the
system register (SR bits in write mode). In the same register there are 5 bits that can be
read back (SR bits in read mode) and provide 2 diagnostic functions, whereas the other 3
bits are for internal usage (TEST1, TEST2, and TEST3).
Two bits report the diagnostic status of the two internal monitoring functions:
–
OTF: over temperature flag. If an overheating occurs (junction temperature
exceeds 150 °C), the OTF I²C bit is set to “1”.
–
OLF: overload flag. If the output current required exceeds the current limit
threshold or a short circuit occurs, the OLF I²C bit is set to “1”.
Moreover, three bits report the last output voltage register status (EN, VSEL, LLC) received
by the I²C. The LNBH23L I²C interface address can be selected from two different
addresses by setting the voltage level of the dedicated ADDR pin according to Table 1:
Table 1.
1.3.1
LNBH23L I²C addresses
Pin Set-up
Write (HEX)
Read (HEX)
ADDR=Low or floating
0x14
0x15
ADDR=High
0x16
0x17
Reserved I²C address
The device has another I²C address reserved only for internal usage, see Table 2.
Table 2.
LNBH23L other I²C addresses
Pin Set-up
Write (HEX)
Read (HEX)
ADDR=Low/High or floating
0x10
0x11
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Block diagram and pin function description
1.4
AN3115
DiSEqC™ 1.X implementation through EXTM pin
The EXTM pin is an analog input to generate the 22 kHz tone superimposed to the VoRX DC
output voltage. If the EXTM pin is used, the internal 22 kHz generator must be kept OFF
(TTX pin or TTX bit set LOW). A cheaper circuit must be used to couple the modulating
signal source to the EXTM pin (see Figure 2).
The EXTM pin modulates the VoRX voltage through the series decoupling capacitor, so that:
VoRX (AC) = VEXTM (AC) x GEXTM
Where:
- VoRX (AC) and VEXTM (AC) are, respectively, the peak to peak voltage on the VoRX and
EXTM pin
- GEXTM is the voltage gain from EXTM to VoRX.
In order to avoid the 22 kHz tone distortion, a dummy output load may be necessary, strictly
dependent on the output bus capacitance.
Table 3.
Output load
Output bus capacitance
Output load
< 50 nF
10 mA
250 nF (EUTELSAT spec.)
30 mA
750 nF (DIRECT TV spec.)
80 mA
For the correct DiSEqC implementation, during tone transmission, it is most important that
the DiSEqC_out pin of the 22 kHz IC controller, is set in low impedance and vice versa,
during no-tone transmission, it must be set in high impedance.
Figure 2 shows an example circuit as an appropriate solution with a 22 kHz IC controller to
drive the EXTM pin for the DiSEqC implementation.
Figure 2.
EXTM example of use with 22 kHz IC controller
VDD 3V3
LNBH23L
4K7
22 KHz IC
controller
R2
Vtone signal
6/28
R1
C1
EXTM pin
1 µF
R3
Doc ID 16830 Rev 3
VoRX
ZEXTM
15 K
4K7
RPD
DISEQC_OUT
VoRx OUTPUT
AN3115
Figure 3.
Block diagram and pin function description
DiSEqC 1.X tone burst with 22 kHz IC controller
High-Z
STATE
High-Z
STATE
High-Z
STATE
VoRx OUTPUT
Vtone signal
Push -pull
Action
1.5
Push -pull
Action
DiSEqC 1.X Implementation through VoTX and EXTM
If an external 22 kHz tone source is not available, it is possible to use the internal 22 kHz
tone generator signal available through the VoTX pin to drive the EXTM pin. In this way the
VoTX 22 kHz signal is superimposed to the VoRX DC voltage to generate the LNB output 22
kHz tone (see Figure 6). The internal 22 kHz tone generator, available through the VoTX pin,
must be activated during the 22 kHz transmission by the DSQIN pin or by the TEN bit. The
DSQIN internal circuit activates the 22 kHz tone on the VoTX output with 0.5 cycles ± 25 µs
delay from the TTL signal present on the DSQIN pin, and it stops with 1 cycle ± 25 µs delay
after the TTL signal is expired. The VoTX pin internal circuit must be preventively set ON by
the TTX function. This can be controlled both through the TTX pin and the I²C bit. As soon
as the tone transmission is expired, the VoTX must be disabled by setting the TTX to LOW.
The 13 / 18 V power supply is always provided to the LNB from the VoRX pin.
1.6
PDC optional circuit for DiSEqC 1.X applications using VoTX
signal on to EXTM pin and 22 kHz tone controlled by DSQIN
pin
In some applications, at light output current (< 50 mA) having a heavy LNB output capacitive
load, the 22 kHz tone can be distorted. In this case it is possible to add the “Optional”
external components described on Section 2.7.
1.7
22 kHz oscillator
The internal 22 kHz tone generator is factory-trimmed in accordance with current standards
and can be selected by the I²C interface TTX bit (or TTX pin) and controlled by the DSQIN
pin (TTL compatible), which allows immediate DiSEqC data encoding. If the 22 kHz tone
presence is requested in continuous mode, the internal oscillator can be activated by the I²C
Doc ID 16830 Rev 3
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Block diagram and pin function description
AN3115
interface TEN bit. The rise and fall edges are controlled to be in the 5 µs to 15 µs range, 8 µs
typ for 22 kHz. The Duty cycle is 50 % typ., it modulates the DC output with a 0.650 VPP
(typ.) amplitude as well as the DSQIN pin.
1.8
DiSEqC communication
The following steps must be taken to ensure the correct implementation of the DiSEqC
communication:
Figure 4.
DiSEqC timing control
LNBout
DSQIN
> 500µs
µ
> 200 µs
TTX
T0
T2 T3
T1
DiSEqC Transmit Mode
1.9
DiSEqC Receive Mode
●
T0: Before starting the DiSEqC transmission. The TTX function must be activated
(through the TTX pin or TTX I²C bit);
●
T1: After 500 µs minimum, the IC is ready to receive the DiSEqC code through the
DSQIN pin (or, alternatively, the TEN I²C bit can be set to HIGH to activate the 22 kHz
burst);
●
T2: When the transmission is elapsed, the TTX function is set to LOW (through the TTX
pin or TTX I²C bit) not earlier than 200 µsec after the last falling edge of the DiSEqC
code.
Linear post-regulator, modulator and protection
The output voltage selection and the current selection commands join this block, which
manages the LNB output function. This block gives feedback to the I²C interface from the
diagnostic block, regarding the status of the thermal protection, over current protection, and
output settings.
1.10
Pin description
The LNBH23L is available in an exposed pad QFN-32 package for surface mount assembly.
Figure 5 shows the device pin-out and Table 4 briefly summarizes the pin function.
8/28
Doc ID 16830 Rev 3
AN3115
Figure 5.
Block diagram and pin function description
LNBH23L pin configuration
Doc ID 16830 Rev 3
9/28
Block diagram and pin function description
Table 4.
AN3115
LNBH23L pin description
QFN 5x5
pin n°
Symbol
Name
19
VCC
Supply input
8 to 15 V IC DC-DC power supply
18
VCC–L
Supply input
8 to 15 V analog power supply
4
LX
NMos drain
Integrated N-channel Power MOSFET Drain
27
VUP
Step-up voltage
Input of the linear post-regulator. The voltage on this pin is monitored
by the internal step-up controller to keep a minimum dropout across
the linear pass transistor.
21
VoRX
LDO output port
Output of the linear post-regulator
22
VoTX
6
SDA
Serial data
Bi-directional data from/to the I²C bus
9
SCL
Serial clock
Clock from the I²C bus
12
DSQIN
DiSEqC input
14
TTX
TTX enable
29
Reserved
Reserved
11
PDC
Pull-down control
To be connected to the external NPN transistor base to reduce the 22
kHz tone distortion in case of heavy capacitive load at light output
current. If not used it can be left floating.
13
EXTM
External
modulation
External Modulation Input acts on VoRX linear regulator output to
superimpose an external 22 kHz signal. Needs DC decoupling to the
AC source. If not used it can be left floating.
5
P-GND
Power ground
ePad
ePad
ePad
20
A-GND
Analog ground
Pin function
Output port during
TX Output to the LNB
22 kHz tone TX
This pin accepts the DiSEqC code from the main microcontroller. The
LNBH23L uses this code to modulate the internally-generated 22 kHz
carrier. Set this pin to ground if not used.
This pin, as well as the TTX I²C bit of the system register, is used to
control the TTX function enable before starting the 22 kHz tone
transmission. Set this pin floating or to GND if not used.
To be connected to GND
DC-DC converter power ground to be connected directly below the
ePad of the PCB top GND layer.
On the bottom side of the QFN-32 package. It must be connected with
power ground and to the ground layer through vias to dissipate heat.
Analog circuits ground
Needed for internal preregulator filtering. The BYP pin is intended
only to connect an external ceramic capacitor. Any connection of this
pin to an external current or voltage sources may cause permanent
damage to the device.
15
BYP
Bypass capacitor
10
ADDR
Address setting
Two I²C bus addresses available by setting the ADDR pin voltage
level.
28
ISEL
Current selection
The resistor RSEL connected between ISEL and GND defines the
linear regulator current limit threshold by the equation: IMAX
(typ.)=10000/ RSEL.
30
Reserved
Reserved
1, 2, 3, 7,
8, 16, 17,
23, 24, 25,
26, 31, 32
N.C.
Not connected
10/28
To be left floating. Do not connect to GND
Not internally connected pins
Doc ID 16830 Rev 3
AN3115
2
Component selection guidelines
Component selection guidelines
The LNBH23L application schematic in Figure 6 shows the typical configuration for a single
LNB power supply.
Figure 6.
LNBH23L typical application circuit with internal tone generator
D3
1N4007
Vup
VoTX
C4
470nF
C3
220uF
R9
1.5KOhm
C6
470nF
to LNB
500 mA max
C15
LNBH23L
D1
STPS130A
EXTM
47 nF
VoRX
LX
C10
220nF
L1
22uH
D2
BAT43
D6
N.C.
Vcc
Vin
12 V
Vcc -L
C1
100uF
C2
100nF
PDC
C8
220nF
I2 C Bus
{
SDA
DSQIN
SCL
ADDR
ISEL
TTX
P-GND
Note:
A -GND
R2 (RSEL)
15kOhm
Byp
C11
220nF
TVS D6 diode to be used if surge protection is required (see Section 2.4).
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Component selection guidelines
Table 5.
AN3115
LNBH23L demo-board BOM list
Index
Quantity
Reference
1
1
R2
15 kΩ 1/8 W (see Section 2.2)
1206
2
1
R5
2.2 kΩ 1/8 W (see Section 2.7)
1206
3
1
R7
22 Ω 1/2 W (see Section 2.7)
1206
4
1
R8
150 Ω 1/2 W (see Section 2.7)
1206
5
1
R9
1.5 kΩ 1/8 W (see Section 2.8)
1206
6
3
C8, C10, C11
0.22 µF
1206
7
1
C15
47 nF
1206
8
1
C14
1 nF
1206
9
2
C4, C6
0.47 µF (See Section 2.5)
1206
10
1
C1
100 µF > 25 V ESR = 150 mΩ ÷ 350 mΩ Higher
value is suitable (see Section 2.6)
El.Al. Radial
11
1
C3
220µF > 25 V ESR = 150 mΩ ÷ 350 mΩ (see
Section 2.5)
El.Al. Radial
12
1
L1
22 µH Inductor with ISAT > IPEAK (see Section 2.1)
13
1
D1
STPS130A (see Section 2.3)
14
1
D2
BAT43 (or any Schottky diode with IF(AV) > 0.2 A,
VRRM > 25 V) or BAT30, BAT54, TMM BAT43,
1N5818 (See Section 2.9)
15
1
D3
1N4001/1N4007 or equivalent
16
1
IC1
LNBH23L
17
1
TR1
BC817
SOT23-3L
18
1
D8
1N4148
SMD
19
2
CN3, CN4
Strip 4p M
HDR1X4
20
2
CN2, CN5
Strip 3p M
HDR1X3
21
3
JP1, 3.3V, CN1
Strip 2p M
HDR1X2
12/28
Value / generic part number
Doc ID 16830 Rev 3
Package
Radial
SMB
DO-35
DIODE-0.4
QFN32
AN3115
2.1
Component selection guidelines
DC-DC converter inductor (L1)
The LNBH23L operates with a standard 22 µH inductor for the entire range of supply
voltages and load current. The Inductor saturation current rating (where inductance is
approximately 70 % of zero current inductance) must be greater than the switch peak
current (ISAT > IPEAK) calculated at:
–
maximum load (IOUTmax);
–
minimum input voltage (VINmin);
–
maximum DC-DC output voltage (VUPmax = VOUTmax + 0.75 V typ.)
In this condition the switch peak current is calculated using the formula in Equation 1:
Equation 1
Ipe ak =
V U P m a x* IO U T m a x
V IN m in ⎛
V IN m in ⎞
+
⎜1 −
⎟
E ff * V IN m in
2 LF
VUP m ax ⎠
⎝
where:
–
Eff is the efficiency of the DC-DC converter (93 % typ. at highest load)
–
L is the inductance (22 µH typ.)
–
F is the PWM frequency (220 kHz typ.)
Example:
Application conditions:
VOUTmax = 19.2 V (supposing EN=VSEL=1, LLC=0)
VINmin = 11 V
VUPmax = VOUTmax + VDROP = 19.2 V + 0.75 V = 19.95 V
IOUTmax = 500 mA
Eff = 90 % (worst-case in these conditions)
Based on Equation 1 and the preceding application conditions, IPEAK is:
Ipeak =
19.95 ∗ 0.5
11
11 ⎞
⎛
+
⎜1 −
⎟ = 1.52A
−
6
3
0.9 ∗ 11
2 * 22 * 10 * 220 * 10 ⎝ 19.95 ⎠
Then, in this example, an inductor with saturation current > 1.52 A should be recommended.
Several inductors suitable for the LNBH23L are listed in Table 6, although there are many
other manufacturers and devices that can be used. Consult each manufacturer for more
detailed information and for their entire selection of related parts, since many different
shapes and sizes are available. Ferrite core inductors should be used to obtain the best
efficiency. Choose an inductor that can handle at least the IPEAK current without saturating,
and ensure that the inductor has a low DCR (copper wire resistance) to minimize power
losses and, consequently, to maximize the total efficiency.
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Component selection guidelines
Table 6.
2.2
AN3115
Recommended Inductors
Vendor
Part number
ISAT (A)
DRC (m?)
Mounting type
Sumida
CD104-220MC
RHC110-220M
1.6
2.4
67
88
SMD
Through-hole
Toko
822LY-220K
824LY-220K
A671HN-220L
A814LY-220M
1.3
1.72
2.44
2.0
70
76
21
75
Through-hole
Through-hole
Through-hole
SMD
Panasonic
ELC08D220E
ELC10D220E
1.8
3.2
51
40
Through-hole
Through-hole
Coilcraft
DC1012-223
PVC-0-223-03
DO3316P-223
2.5
3
2.6
46
35
85
Through-hole
Through-hole
SMD
Output current limit selection (R2-RSEL)
The linear regulator current limit threshold can be set through an external resistor connected
to the ISEL pin. The resistor value defines the typical output current threshold limit by the
equation:
Equation 2
Im ax ( A) =
10000
Rsel
Where RSEL is the resistor connected between ISEL and GND. The highest selectable
current limit threshold is 0.650 A typ. with RSEL = 15 kΩ
To set the current limitation, ±15 % tolerance, referred to the typical Imax current value, must
be considered. At this tolerance the tolerance of the RSEL resistor must be added.
For example:
RSEL resistor = 15 kΩ ± 1 %
Im ax ( typ ) =
10000
= 666 mA
15000
To calculate the Imax(min) and Imax(max) values:
TotToleran ce = 15 % + 1 % = 16 %
Where:
–
–
14/28
15 % is the LNBH23L tolerance
1 % is the RSEL tolerance
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Component selection guidelines
And then:
Im ax (min) = 666 mA − 16 % = 559 mA
Im ax (min) = 666 mA + 16 % = 772 mA
Figure 7.
Typical output current limiting vs. RSEL
1.4
VCC=12V
1.2
IMAX [mA]
1
0.8
0.6
0.4
0.2
0
10
12
14
16
18
20
22
24
26
28
30
32
RSEL [K ]
The formula below allows correct dimensioning of the RSEL total power dissipation:
Rsel (I) =
1V
Rsel ( Ω )
Supposing:
RSEL resistor = 15 kΩ
Rsel (I) =
1V
= 66 μ A
15000 ( Ω )
WRSEL = RSEL(I)2 x RSEL = (66 µA) 2 x 15000 = 65 µW
2.3
DC-DC converter schottky diode (D1)
In typical application conditions it is beneficial to use a 1 A Schottky diode which is suitable
for the LNBH23L DC-DC converter. Taking into account that the DC-DC converter Schottky
diode must be selected depending on the application conditions (VRRM > 25 V), in general a
Schottky diode such as the STPS130A is suitable.
The average current flowing through the Schottky diode is lower than IPEAK and can be
calculated by Equation 3. In worst-case conditions, such as low input voltage and higher
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output current, a Schottky diode capable of supporting the IPEAK should be selected. IPEAK
can be calculated using Equation 1.
Equation 3
Id = Iout ×
Table 7.
Vout
Vin
Recommended Schottky diode
Vendor
Part number
IF (av)
VF (max)
1N5818
1A
0.50 V
1N5819
1A
0.55 V
STPS130A
1A
0.46 V
STPS1L30A
1A
0.30 V
STPS2L30A
2A
0.45 V
1N5822
3A
0.52 V
STPS340
3A
0.63 V
STPS3L40A
3A
0.5 V
STMicroelectronics
2.4
TVS diode (D6)
The LNBH23L device is directly connected to the antenna cable in a set-top box.
Atmospheric phenomenon can cause high voltage discharges on the antenna cable causing
damage to the attached devices. In applications where it is required to protect against
lightning surges, transient voltage suppressor (TVS) devices like LNBTVSx-22xx can be
used to protect the LNBH23L and the other devices electrically connected to the antenna
cable.The LNBTVSx-22xx diodes, developed by STMicroelectronics, are dedicated to
lightning and electrical overstress surge protection for LNBHxx voltage regulators. These
protection diodes were designed to comply with the stringent IEC61000-4-5 standard with
surges up to 500 A in a whole range of products.
Note:
TVS diodes have intrinsic capacitance that attenuates the RF signal. For this reason, the
LNBTVSx-22xx cannot be directly connected to the IF (RX/TX) cable connector that carries
the RF signals coming from the LNB. To suppress effects of the intrinsic capacitance, an
inductance must be placed in series with the TVS diode (see Figure 6 example). The goal of
the L series inductance added to the CLNBTVS is to be transparent at 22 kHz and to reject
frequencies higher than 900 MHz.
The value of the series inductance is usually >13 nH, with a current capability higher than
the IPP (peak pulse current) expected during the surge.
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Figure 8.
Component selection guidelines
Example of LNBTVS diode connection
D3
1N4007
VoTX
IF Connector
R9
C15
LNBH23L
Lseries >13nH
EXTM
VoRX
C10
D6
LNBTVSx -22xx
D2
The selection of the TVS diode must be based on the maximum peak power dissipation that
the diode is capable of supporting.
Table 8.
Recommended LNBTVS
Vendor
Part number
VBRTYP (V)
Ipp (A)
8/20 µs
LNBTVS4-220S
23.1
334
LNBTVS4-221S
23.1
334
LNBTVS4-222S
23.1
334
LNBTVS6-221S
23.1
500
STMicroelectronics
Select the TVS diode which is capable of supporting the required Ipp (A) value indicated in
Table 8.
2.5
DC-DC output capacitors (C3, C4, C6) and ferrite bead
An electrolytic low cost capacitor is needed on the DC-DC converter output stage (C3 in
Figure 6). Moreover, two ceramic capacitors are recommended to reduce the high
frequency switching noise. The switching noise is due to the voltage spikes of the fast
switching action of the output switch, and to the parasitic inductance of the output
capacitors. To minimize these voltage spikes, special low-inductance ceramic capacitors
can be used, and their lead lengths must be kept short and as close as possible to the IC
pins (C4 and C6 in Figure 9). In case of high switching noise, it is possible to increase the
C6 capacitor up to 4.7 µF, 2.2 µF is a good compromise to reduce the switching noise.
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Component selection guidelines
Figure 9.
AN3115
DC-DC converter output stage with ferrite bead
The most important parameter for the DC-DC output electrolytic capacitors is the effective
series resistance (ESR). The DC-DC converter control loop circuit has been designed to
work properly with low-cost electrolytic capacitors which have ESR in the range of 200 mΩ.
A 220 µF with ESR between 100 mΩ and 350 mΩ is a good choice in most application
conditions. In case it is requested to further reduce the switching noise, a ferrite bead with a
current rating of at least 2 A and impedance higher than 60 Ω at 100 MHz could be used.
In this case It is recommended to use two electrolytic capacitors of 100 µF (see C3 and C3A
in Figure 9) with ESR between 150 mΩ and 350 mΩ adding the ferrite bead in accordance
to Figure 9.
The DC-DC capacitor's voltage rating must be at least 25 V, but higher voltage capacitors
are recommendable.
2.6
Input capacitors (C1)
An electrolytic bypass capacitor (C1 in Figure 6) between 100 µF and 470 µF, located close
to the LNBH23L, is needed for stable operation. In any case, a ceramic capacitor (C2 in
Figure 6) between 100 nF and 470 nF is recommended to reduce the switching noise at the
input voltage VCC pins.
2.7
PDC optional external circuit
This optional circuit, internally controlled by the PDC output pin, acts as an active pull-down
discharging the output capacitance only when the internal 22 kHz tone is activated
(TEN=TTX=1 or DSQIN=1).
This optional circuit is not needed in standard applications having IOUT > 50 mA and
capacitive load up to 250 nF where the PDC pin can be left floating.
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Component selection guidelines
Figure 10. Application circuit with PDC optional solution
D3
1N4007
Vup
VoTX
C4
470 nF
C3
220 µF
C5
N.C.
R9
1.5 kOhm
C6
470 nF
to LNB
500 mA max
C15
EXTM
47 nF
D1
STPS130A
LNBH23L
LX
VoRX
C10
220 nF
L1
22 µH
D2
BAT43
D6
N.C.
Vcc
*R8
150 Ohm
Vin
12 V
D8
1N4148
Vcc -L
C1
100 µF
C2
100 nF
*TR1
BC317
PDC
C8
220 nF
*R5
2.2 kOhm
I2C Bus
{
*C14
1 nF
SDA
DSQIN
SCL
*R7
22 Ohm
3.3 V
ADDR
ISEL
TTX
P-GND
A -GND
R2 (RSEL)
15 kOhm
Byp
(*)OPTIONAL components.
To be used only in case
of heavy capacitive load
C11
220 nF
The formula to calculate the transistor IC current with PDC circuit is:
Equation 4
IC =
VBYP - VD - VBE
R5
R7 +
TR1hfe
The current flows through R8, TR1 and R7 during fall time of 22 kHz tone and the power
dissipated by these passive components is 1/3 because the D.C. is 30 % (see Figure 11).
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Figure 11. PDC optional circuit load calculation
Figure 12. PDC circuit waveform
2.8
EXTM-VOTX resistor (R9)
The LNBH23L device offers the possibility to customize the output tone amplitude through
the R9 resistor variation. According to the graph in Figure 13, the R9 resistor can be slightly
modified to change the output tone amplitude when the internal 22 kHz tone generator is
used. Values between 1 kΩ and 2.7 kΩ are recommended.
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Component selection guidelines
Figure 13. Tone amplitude vs. R9 value
0.9
Tone Amplitude (Vpp)
0.85
0.8
0.75
0.7
0.65
0.6
0.55
0.5
0.45
0.4
0.35
0.3
0.5
1
1.5
2
2.5
3
3.5
4
4.5
R9 value (kohm)
2.9
Undervoltage protection diode (D2)
During a short-circuit event on the LNB output, negative voltage spikes may occur on the
VoRX pin. To prevent reliability problems, a low-cost Schottky diode with low VF clamping
voltage is used between this pin and GND (see D2 in Figure 6). It is recommended to place
the protection diode cathode as close as possible to the VoRX pin.
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Layout guidelines
3
AN3115
Layout guidelines
Due to high current levels and fast switching waveforms, which radiate noise, a proper
printed circuit board (PCB) layout is essential. Sensitive analog grounds can be protected by
using a star ground configuration. Also, lead lengths should be minimized to reduce stray
capacitance, trace resistance, and radiated noise. Ground noise can be minimized by
connecting GND, the input bypass capacitor ground lead, and the output filter capacitor
ground lead to a single point (star ground configuration). Place input bypass capacitors (C1,
C2 and C8) as close as possible to VCC and GND, and the DC-DC output capacitors (C3,
C4 and C6) as close as possible to VUP. Excessive noise at the VCC input may falsely trigger
the undervoltage protection circuitry, resetting the I²C internal registers. If this occurs, the
registers are set to zero and the LNBH23L is put into shutdown mode.
An LNB power supply demonstration board is available.
3.1
PCB layout
Any switch-mode power supply requires a good PCB layout in order to achieve maximum
performance. Component placement, and GND trace routing and width, are the major
issues. Basic rules commonly used for DC-DC converters for good PCB layout should be
followed. All traces carrying current should be drawn on the PCB as short and as thick as
possible. This should be done to minimize resistive and inductive parasitic effects, and
increase system efficiency. White arrows indicate the suggested PCB (ring) ground plane to
avoid spikes on the output voltage (this is related to the switching side of the LNBH23L).
Good soldering of the ePad helps on this issue.
Figure 14. PBC top layer
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Layout guidelines
Figure 15. PBC bottom layer
Figure 16. PCB components layout
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Layout guidelines
3.2
AN3115
PCB Thermal managing
The LNBH23L power dissipation inside the IC is mainly due to the DC-DC integrated
MOSFET power loss plus the linear regulator power dissipation. The total power dissipation
calculated, considering both the DC-DC and linear regulator power loss at the maximum
output current (500 mA) with 18 V for LNB output and VIN = 11 V, is around 1 W. The heat
generated due to this power dissipation level requires a suitable heat-sink to keep the
junction temperature below the over temperature protection threshold at the rated ambient
temperature inside the set-top box.
For example: assuming a 70 °C max for the ambient temperature inside the STB case and a
125 °C maximum junction temperature for the LNBH23L, the total RthJA is less than 50
°C/W.
The RthJA for the QFN32 package used for the LNBH23L can be as low as 35 °C/W. Based
on thermal resistance tests performed on the LNBH23L ST demonstration board, this result
is achievable with a minimum of a 4x4 cm² copper area placed just below the IC body (see
Figure 17). Better performance with a smaller copper area may be achievable using four
layers (2s2p) PCB.
Usually the copper area is obtained by using the ground layer of a multi-layer PCB soldered
below the IC exposed pad. In Figure 14 an example of a layout for the QFN32 package with
a dual layer PCB is shown, where the IC exposed pad is connected to the ground layer and
the square dissipating area is thermally connected through 9 via holes filled by solder.
Figure 17. Typical junction to ambient thermal resistance with dual layer PCB, 1oz, 9 thermal
vias
80
70
RthJA (°C/W)
60
50
40
30
20
10
0
0
2
4
6
8
10
12
14
16
Copper Area (cm²)
The best thermal and electrical performance can be achieved when an array of copper vias
barrel plating is incorporated in the land pattern at 1.2 mm grid. It is also recommended that
the via diameter should be 0.30 mm to 0.33 mm with 1 oz copper via barrel plating.
If the copper plating does not plug the vias, a solder mask material must be used to cap the
vias with a dimension equal to the via diameter + 0.1 mm minimum. This prevents the solder
from not being well spread through the thermal via and potentially creating a solder void
between the package bottom and the ground plane of the PCB.
Taking into account that the solder mask diameter should be at least 0.1 mm larger than the
via diameter.
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Layout guidelines
However, different layouts are also possible. Basic principles suggest keeping the IC and its
ground exposed pad approximately in the middle of the dissipating area; to provide as many
vias as possible; to design a dissipating area having a shape as square as possible and not
interrupted by other copper traces.
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Startup procedure
4
AN3115
Startup procedure
Testing the demonstration board requires a PC with a parallel port (ECP printer port), an I²C
bus interface, software (LNBxx control suite), a dual-output power supply (3 A clamp current
or higher) and an electronic load.
–
Step 1: Install the LNBxx control suite software (Software installation)
–
Step 2: Plug the I²C connector on CN3.
–
Step 3: Supply the demo-board through CN1.
–
Step 4: Manage the demo-board through LNBxx control suite software
Figure 18. PCB connector
CN1
To supply the demo-board.
(Typ. 12 V DC). Use a power
supply with a 3 A clamp current or
higher.
CN5
To supply LNB.
LNBOUT = VOUT test
point.
CN2
CN3
ADDR tip : Connect ADDR pin to ground to set
I2C address = 02.
I2C interface connections:
For data transmissions from I2C interface to the
LNBH23L and vice-versa. Care should be
taken to ensure proper connection of the I2C
interface.
+ 3.3 V Connector
To supply the PDC
circuit
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Revision history
5
Revision history
Table 9.
Document revision history
Date
Revision
Changes
03-Oct-2010
1
Initial release
29-Nov-2010
2
Modified Section 1.3.1: Reserved I²C address on page 5.
28-Jan-2011
3
Modified R7 value Table 5 on page 12.
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AN3115
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