dm00066548

AN4175
Application note
LNBH25 supply and control IC with step-up and I²C interface
Introduction
This application note provides additional information and suggestions about the correct use of the
LNBH25 device. All waveforms shown are based on the evaluation boards STEVAL-CBL009V1 and
STEVAL-CBL010V1 described in Section 5: "Component selection guide" . The LNBH25 is a low-cost
integrated solution for supplying/interfacing satellite LNB modules. Its performance is very good with the
minimum quantity of external components. It includes all functions needed for the LNB supply and
2
interface, in accordance with international standards. Moreover, it includes an I C bus interface and,
thanks to a fully integrated step-up DC-DC converter, it works with a single input voltage supply range
from 8 V to 16 V.
Figure 1: Internal block diagram
ADDR SCL
SDA
LX
PWM CTRL
I2C digital core
DETIN
DSQOUT
Tone
detector
DAC
Drop control
Tone ctrl
Diagnostics
Protections
FLT
Isense
DSQIN
PGND
VUP
Current
limit
selection
Linear
regulator
Gate ctrl
BPSW
VOUT
Voltage
reference
GND
September 2015
BYP VCC
ISEL
DocID023736 Rev 2
GIPG2807151625
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www.st.com
Contents
AN4175
Contents
1
2
Block diagram description.............................................................. 5
1.1
Step-up controller .............................................................................. 5
1.2
Voltage reference block .................................................................... 5
1.3
I2C interface digital core and diagnostic ............................................ 5
1.4
Tone detector .................................................................................... 6
1.5
Linear post-regulator and current limit ............................................... 6
DiSEqC data encoding .................................................................... 7
2.1
22 kHz external source (EXTM=TEN=1) ........................................... 7
2.2
DiSEqC data envelope source (EXTM=0; TEN=1) ............................ 8
2.3
22 kHz tone in continuous mode (EXTM=0; TEN=1; DSQIN pin=H)11
3
DiSEqC 2.0 implementation .......................................................... 12
4
Pin description .............................................................................. 14
5
Component selection guide .......................................................... 16
6
7
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5.1
Input capacitors ............................................................................... 18
5.2
DC-DC converter output capacitors ................................................ 18
5.3
DC-DC converter Schotty diode ...................................................... 18
5.4
DC-DC converter inductor ............................................................... 19
5.5
Output current limit selection ........................................................... 20
5.6
Undervoltage diode protection ........................................................ 20
5.7
DiSEqC 2.0 implementation and inductor selection ........................ 21
5.8
TVS diode ....................................................................................... 21
Layout guidelines .......................................................................... 23
6.1
PCB layout ...................................................................................... 23
6.2
Start-up procedure .......................................................................... 26
Revision history ............................................................................ 28
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AN4175
List of tables
List of tables
Table 1: Pin description ............................................................................................................................ 14
Table 2: LNBH25 evaluation board BOM list ............................................................................................ 17
Table 3: Recommended Schottky diode ................................................................................................... 19
Table 4: Recommended inductors ............................................................................................................ 20
Table 5: Recommended inductors for output R-L filter ............................................................................. 21
Table 6: Recommended ST LNBTVS ....................................................................................................... 22
Table 7: Document revision history .......................................................................................................... 28
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List of figures
AN4175
List of figures
Figure 1: Internal block diagram ................................................................................................................. 1
Figure 2: 22 kHz external source ................................................................................................................ 7
Figure 3: 22 kHz external source activation delay ...................................................................................... 8
Figure 4: 22 kHz external source deactivation delay .................................................................................. 8
Figure 5: DiSEqC data envelope source .................................................................................................... 9
Figure 6: DiSEqC data envelope source activation delay ........................................................................ 10
Figure 7: DiSEqC data envelope source deactivation delay .................................................................... 10
Figure 8: 22 kHz tone in continuous mode ............................................................................................... 11
Figure 9: DSQOUT output pin .................................................................................................................. 12
Figure 10: BPSW pin behavior during tone transmission ......................................................................... 13
Figure 11: Pin configuration (marking view) ............................................................................................. 14
Figure 12: STEVAL-CBL009V1 evaluation board schematic for DiSEqC1.x communication .................. 16
Figure 13: STEVAL-CBL010V1 evaluation board schematic for DiSEqC 2.0 communication................. 17
Figure 14: DC-DC converter output stage with ferrite bead ..................................................................... 18
Figure 15: Recommended TVS diode connection .................................................................................... 22
Figure 16: STEVAL-CBL009V1 top layer ................................................................................................. 23
Figure 17: STEVAL-CBL009V1 bottom layer ........................................................................................... 24
Figure 18: STEVAL-CBL009V1 component layout ................................................................................... 24
Figure 19: STEVAL-CBL010V1 top layer ................................................................................................. 25
Figure 20: STEVAL-CBL010V1 bottom layer ........................................................................................... 25
Figure 21: STEVAL-CBL010V1 component layout ................................................................................... 26
Figure 22: PCB connector ........................................................................................................................ 27
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1
Block diagram description
Block diagram description
The LNBH25 internal blocks are described in the following sections.
1.1
Step-up controller
The LNBH25 features a built-in step-up DC-DC converter that, from a single supply source
ranging from 8 V to 16 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 12: "STEVAL-CBL009V1 evaluation board
schematic for DiSEqC1.x communication" and Figure 13: "STEVAL-CBL010V1 evaluation
board schematic for DiSEqC 2.0 communication"). No external power MOSFET is needed.
1.2
Voltage reference block
This block includes the undervoltage lockout circuit, which disables the whole circuit when
the supplied VCC pin drops below a fixed threshold (4.7 V typ.) and a power-on reset sets
2
all the I C registers to zero when the VCC turns on and rises from zero above the threshold
(4.8 V typ.). If the input voltage is lower than LPD (low power diagnostic) minimum
thresholds (6.7 V typ.), the PNG I²C bit is set to “1” by the voltage reference block and the
FLT pin is set low.
1.3
I2C interface digital core and diagnostic
2
The device main functions are controlled by I C bus, the data communication protocol from
the main microprocessor to the LNBH25 and vice versa, which takes place through SDA
and SCL pins. By writing to 4 control registers, all the LNBH25 functions can be managed.
Moreover, 2 status registers can be read back and 8 diagnostic functions are received by
2
the IC. The LNBH25 I C interface address can be selected between two different
addresses by setting the voltage level of the dedicated ADDR pin.
Eight bits report the diagnostic status of eight internal monitoring functions:
OLF: overload fault. If the output current required exceeds the current limit threshold or a
2
short-circuit occurs, OLF I C bit is set to "1".
OTF: overtemperature fault. If an overheating occurs, (junction temperature exceeds 150
2
°C typ.) the OTF I C bit is set to "1".
PNG: power not good. If the input voltage (VCC pin) is lower than LPD minimum threshold
2
(6.7 V typ.) the PNG I C bit is set to "1".
VMON: voltage monitoring. If the output voltage (VOUT pin) is lower than VMON
2
specification thresholds, the VOM I C bit is set to "1".
PDO: pull-down overcurrent. If the device output rises to a voltage level higher than the
2
output nominal voltage selected, PDO I C bit is set to "1". This may happen due to an
external voltage source present on the LNB output (VOUT pin).
TDET: tone detection. 22 kHz tone presence is detected on the DETIN pin.
TMON: tone monitoring. If the 22 kHz tone amplitude and/or the tone frequency is out of
the guaranteed limits (refer to the datasheet.), the TMON I²C bit is set to "1".
IMON: minimum output current diagnostic to detect if no LNB is connected on the bus or
cable is not connected to the IRD, the LNBH25 is provided with a minimum output current
flag by the IMON I²C bit, which is set to "1" if the output current is lower than 12 mA (typ.).
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Block diagram description
1.4
AN4175
Tone detector
This block provides a complete circuit to decode the 22 kHz burst code present on the
DETIN pin in a digital signal by the DSQOUT pin where an open drain MOSFET is
connected. The tone is also monitored and a dedicated bit (TMON) provides the diagnostic
function described in Section 1.1: "Step-up controller".
1.5
Linear post-regulator and current limit
The output voltage selection and the current selection commands join this block, which
2
manages all the LNB output functions. This block gives feedback to the I C interface
overcurrent protection and output settings. The linear post-regulator current limit threshold
can be set by an external resistor connected to the ISEL pin.
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2
DiSEqC data encoding
DiSEqC data encoding
The internal 22 kHz tone generator is factory-trimmed in accordance with current
DiSEqC™ standards and its waveform is internally controlled by the LNBH25 tone
generator in terms of rise/fall time and amplitude. The 22 kHz tone can be controlled in
different ways through DISQIN logic pin and two I²C bits (EXTM and TEN).
2.1
22 kHz external source (EXTM=TEN=1)
If an external 22 kHz source DiSEqC data is available, it can be connected to the DSQIN
logic pin (TTL compatible). The EXTM and TEN I²C bits must be set to "1". In this case the
frequency and the duty cycle of the output tone are defined by the external 22 kHz signal
on the DSQIN pin.
Figure 2: 22 kHz external source
Before sending the TTL signal to the DSQIN pin, the EXTM and TEN bits must be
previously set to "1". When the DSQIN internal circuit detects the 22 kHz TTL external
signal code, the LNBH25 activates the 22 kHz tone on the VOUT pin with about 1 μs delay
from TTL signal activation, and it stops with about 60 μs delay after the 22 kHz TTL signal
on DSQIN has expired, refer to Figure 3: "22 kHz external source activation delay" and
Figure 4: "22 kHz external source deactivation delay".
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DiSEqC data encoding
AN4175
Figure 3: 22 kHz external source activation delay
Figure 4: 22 kHz external source deactivation delay
2.2
DiSEqC data envelope source (EXTM=0; TEN=1)
Using an external DiSEqC data envelope source connected to the DSQIN logic pin, the I²C
tone control bits must be set: EXTM = 0 and TEN = 1. In this manner, the internal 22 kHz
signal is superimposed to the VOUT DC voltage to generate the LNB output 22 kHz tone.
During the period in which the DSQIN is kept high, the internal control circuit activates the
22 kHz tone output.
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AN4175
DiSEqC data encoding
Figure 5: DiSEqC data envelope source
22 kHz tone on the VOUT pin is active with about 6 μs delay from the DSQIN TTL signal
rising edge, and it stops with a delay time in the range from 15 μs to 60 μs after the 22 kHz
TTL signal on DSQIN has expired (refer to Figure 6: "DiSEqC data envelope source
activation delay" and Figure 7: "DiSEqC data envelope source deactivation delay").
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DiSEqC data encoding
AN4175
Figure 6: DiSEqC data envelope source activation delay
Figure 7: DiSEqC data envelope source deactivation delay
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2.3
DiSEqC data encoding
22 kHz tone in continuous mode (EXTM=0; TEN=1; DSQIN
pin=H)
If a 22 kHz presence is requested in continuous mode, the integrated tone generator can
be activated through the TEN I²C bit. In this case the DSQIN TTL pin must be pulled high
and the EXTM bit set to "0".
Figure 8: 22 kHz tone in continuous mode
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DiSEqC 2.0 implementation
3
AN4175
DiSEqC 2.0 implementation
The built-in 22 kHz tone detector completes the fully bi-directional DiSEqC 2.0 interfacing.
The input pin (DETIN) must be AC coupled to the DiSEqC bus, and extracted PWK data is
available on the DSQOUT pin, please refer to the below figure.
Figure 9: DSQOUT output pin
To comply with the bi-directional DiSEqC 2.0 bus hardware requirements, an output RL
filter is needed. In order to avoid 22 kHz waveform distortion during tone transmission, the
LNBH25 is provided with the BPSW pin to be connected to an external transistor, which
allows the output RL filter in DiSEqC 2.x applications to be bypassed while in transmission
mode (refer to the below figure). Before starting tone transmission by the DSQIN pin, make
sure that the TEN bit is set to "1" and after ending tone transmission, make sure that the
TEN bit is set to 0.
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DiSEqC 2.0 implementation
Figure 10: BPSW pin behavior during tone transmission
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Pin description
4
AN4175
Pin description
The LNBH25 is available in QFN24L with exposed pad package for surface mount
assembly. The below figure shows the device pinout while Table 1 briefly summarizes the
pin functions.
Figure 11: Pin configuration (marking view)
24
NC
23
22
DSQOUT DSQIN
21
20
19
VUP
VOUT
DETIN
1
NC
BPSW
18
2
FLT
VCC
17
3
LX
VBYP
16
4
PGND
GND
15
5
NC
NC
14
6
ADDR
NC
13
SCL
SDA
ISEL
NC
NC
NC
7
8
9
10
11
12
Table 1: Pin description
Pin
Symbol
Name
Function
2
FLT
FLT
Open drain output for IC fault conditions. It is set low in
case of overload (OLF bit) or overheating status (OTF bit)
is detected. To be connected to pull-up resistor (5 V max.)
3
LX
NMOS drain
4
PGND
Power ground
DC-DC converter power ground to be connected directly to
the exposed pad
6
ADDR
Address setting
Two I C bus addresses available by setting the address pin
level voltage
7
SCL
Serial clock
Clock from/to I C bus
8
SDA
Serial data
Bi-directional data from/to I²C bus
9
ISEL
Current
selection
15
GND
Analog ground
Integrated N-channel power MOSFET drain
2
14/29
2
The resistor RSEL connected between ISEL and GND
defines the linear regulator current limit threshold. Refer to
output current limit selection
Analog circuit ground. To be connected directly to the
exposed pad
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AN4175
Pin description
Pin
Symbol
Name
16
BYP
Bypass
capacitor
17
VCC
Supply input
Function
Needed for internal pre-regulator filtering. The BYP pin is
intended to connect an external ceramic capacitor only.
Any connection of this pin to external current or voltage
sources may cause permanent damage to the device
8 to 16 V IC DC-DC power supply
18
BPSW
Switch control
To be connected to an external transistor to be used to
bypass the output RL filter needed in DiSEqC 2.x
applications during the DiSEqC transmitting mode (see
typical application circuits). Set to ground if it is not used
19
DETIN
Tone detector
input
22 kHz tone decoder input, must be AC coupled to the
DiSEqC 2.0 bus. Set to ground if it is not used
20
VOUT
LNB output port
Output of the integrated very low drop linear regulator. See
truth table for voltage selections and description
21
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
DSQIN for
DiSEqC
envelope input
Or external 22
kHz TTL input
It can be used as DiSEqC envelope input or external 22
kHz TTL input depending on the EXTM I²C bit setting as
follows: EXTM=0, TEN=1: it accepts the DiSEqC envelope
code from the main μcontroller. The LNBH25 uses this
code to modulate the internally generated 22 kHz carrier. If
EXTM=TEN=1: it accepts the external 22 kHz logic signals,
which activate the 22 kHz tone output (refer to data
encoding application information). Pull up high if the tone
output is activated by TEN I²C bit only
22
DSQIN
23
DSQOUT
DiSEqC output
Open drain output of the tone detector to the main
microcontroller for DiSEqC 2.0 data decoding. It is low
when tone is detected to the DETIN input pin. Set to
ground if it is not used
Epad
Epad
Exposed pad
To be connected with power ground and to the ground
layer through vias to dissipate heat
1, 5,
10, 11,
12, 13,
14, 24
NC
Not internally
connected
Not internally connected pins. These pins can be
connected to GND to improve thermal performance
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Component selection guide
5
AN4175
Component selection guide
The LNBH25 application schematics in Figure 12: "STEVAL-CBL009V1 evaluation board
schematic for DiSEqC1.x communication" and Figure 13: "STEVAL-CBL010V1 evaluation
board schematic for DiSEqC 2.0 communication" , show the typical configurations for a
single LNB power supply for DiSEqC 1.x and DiSEqC 2.0 communication respectively.
Figure 12: STEVAL-CBL009V1 evaluation board schematic for DiSEqC1.x communication
D2
to LNB
VUP
VOUT
C3
D1
C2
C5
D3
TVS
LX
LNBH25
L1
VIN
12 V
BPSW
C1
DiSEqC
22 kHz
C4
TTL
DSQIN
or
DiSEqC
envelope
DETIN
VCC
ADDR
TTL
I2C Bus
{
DSQOUT
SDA
SCL
FLT
RSEL
ISEL
P- GND
A- GND
BYP
C7
GIPG2907150857LM
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AN4175
Component selection guide
Figure 13: STEVAL-CBL010V1 evaluation board schematic for DiSEqC 2.0 communication
D2
L2
VUP
to LNB
VOUT
C3
D1
C2
C5 D3
LX
LNBH25
R3
L1
R9
TVS
TR1
C6
BPSW
R2
R5
VIN
12 V
VCC
C1
DiSEqC
22 kHz
C4
TTL
DSQIN
or
DiSEqC
envelope
DETIN
ADDR
TTL
I2C Bus {
RSEL
SDA
SCL
ISEL P-GND
DSQOUT
FLT
A -GND
BYP
C7
GIPG2907150920LM
For both pictures, TVS diode has to be used if surge protection is required.
Table 2: LNBH25 evaluation board BOM list
Component
Notes
IC1
LNBH25 (QFN24L) exposed pad
C1
10 μF, 25 V ceramic capacitor
C2
100 μF, 50 V electrolytic capacitor
C3
1 μF, 50 V ceramic capacitor
C6
0.01 µF, 35 V ceramic capacitors
C4, C5, C6
0.22 μF, 50 V ceramic capacitor
D1
STPS130A or any similar Schottky diode
D2
S1A general purpose diode
D3
BAT43 (or any Schottky diode with IF(AV) > 0.2 A, VRRM > 25 V) or BAT30, BAT54,
TMM BAT43, 1N5818
TVS
LNBTVS22-XX TVS protection diode is suggested. Any other solution can be used
depending on the requested surge protection level
L1
10 μH inductor with ISAT>IPEAK
L2
220 μH inductor with current rating higher than the rated output current
TR1
SI2003BDS 30 V PMOS
RSEL
16.2 kΩ 1/16 W resistor
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Component selection guide
AN4175
Component
5.1
Notes
R2 , R3
4.7 kΩ resistor
R5
10 kΩ resistor
R9
15 hm 1/4W resistor
Input capacitors
A ceramic bypass capacitor (C1 in Figure 12: "STEVAL-CBL009V1 evaluation board
schematic for DiSEqC1.x communication" and Figure 13: "STEVAL-CBL010V1 evaluation
board schematic for DiSEqC 2.0 communication" ) between 10 µF and 47 µF placed near
the LNBH25 is needed for a stable operation. In any case, a ceramic capacitor in the range
from 100 nF to 470 nF is recommended to reduce the switching noise on the input voltage
pin (C4 in Figure 12: "STEVAL-CBL009V1 evaluation board schematic for DiSEqC1.x
communication" and Figure 13: "STEVAL-CBL010V1 evaluation board schematic for
DiSEqC 2.0 communication").
5.2
DC-DC converter output capacitors
Low-cost electrolytic capacitors are needed on the DC-DC converter output stage (C2 in
Figure 12 and Figure 13). Moreover, a ceramic capacitor between 1 μF and 4.7 μF is
recommended to reduce high frequency switching noise (C3 in Figure 12 and Figure 13).
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 further reduce switching
noise, a ferrite bead is recommended between the capacitors (refer to Figure 14).
Figure 14: DC-DC converter output stage with ferrite bead
D2
Ferrite
bead
D1
C2
VUP
C3
LX
LNBH 25
L1
GIPG2907151333LM
The capacitor voltage rating must be at least 25 V, but if the highest voltage selection
condition is used (VSEL1= VSEL2= VSEL3= VSEL4 = 1), 35 V or higher voltage capacitors are
suggested.
5.3
DC-DC converter Schotty diode
In typical application conditions, 1 A Schottky diode is suitable for the LNBH25 DC-DC
converter. Taking into consideration that the DC-DC converter Schottky diode must be
selected depending on the application conditions,(V RRM > 25 V) one N-channel Schottky
diode, such as the STPS130A is recommended. The average current flowing through the
Schottky diode is lower than Ipeak and can be calculated using the equation 1. In worst-case
conditions, such as low input voltage and higher output current, a Schottky diode capable
of supporting the Ipeak should be selected. Ipeak can be calculated using equation 2.
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Component selection guide
Equation 1: Id = IOUT x VOUT/VIN
Table 3: Recommended Schottky diode
Vendor
Order code
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
STMicrolectronics
5.4
DC-DC converter inductor
The LNBH25 operates with a 10 µH inductor for the entire range of supply voltage 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 (I peak) calculated at:



maximum load (IOUTmax.)
minimum input voltage (VINmin.)
maximum DC-DC output voltage (VUPmax. = VOUTmax. + 1 V)
In this condition the switch peak current is calculated using the formula in equation 2:
Equation 2:
Ipeak =
VUPmax.· IOUTmax. VINmin.
VIN min. )
+
1(
Eff · VI Nmin.
2LF
VUPmax.
where:
Eff: is the efficiency of the DC-DC converter (93% typ. at the highest load)
L: is the inductance (10 µH typ.)
F: is the PWM frequency (440 kHz typ.)
Here below an example by using 10 µH coil.
The application condition as follows:
VOUTmax. = 19.150 V (supposing VSEL1 = VSEL2 = VSEL4 = 1, VSEL2 = 0)
VINmin. = 11 V
VUPmax. = VOUTmax. +VDROP = 19.150 V+1 V = 20.150 V IOUTmax. = 500 mA
Eff = 90%
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Component selection guide
By using equation 1, Ipeak is:
AN4175
Equation 3:
20.150· 0.5
11
+
Ipeak =
2 ·10 ·10-6 · 440 ·103
0.9·11
11
)=1.23 A
(1- 20.150
Table 4: Recommended inductors
Supplier
Order code
ISAT(A)
DRC(mΩ)
Coilcraft
LPS6235-103MLB
2.3
100
TDK
SLF6045-100M1R6
1.6
39
EPCOS
B82472G6103M
1.9
53
Mounting type
SMT
Several inductors suitable for the LNBH25 are listed in the above table, although there are
many other manufacturers and devices that can be used. Consult each manufacturer for
more detailed information 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 total
efficiency.
5.5
Output current limit selection
The linear regulator current limit threshold can be set through an external resistor
connected to ISEL pin. The resistor value defines the output current limit using the below
equation:
Equation 4 :
Imax. typ. (A)= 13915
1.111
RSEL
with ISET = 0
Imax. typ. (A)= 6808
1.068
RSEL
with ISET=1
where RSEL is the resistor connected between the ISEL pin and GND. The highest
selectable current limit threshold is 1.0 A (typ.) with RSEL = 11.5 kΩ.
5.6
Undervoltage diode protection
During a short-circuit removal on the LNB output, negative voltage spikes may occur on the
VOUT pin. To prevent reliability problems, a low-cost Schottky diode is used between this
pin and GND.
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5.7
Component selection guide
DiSEqC 2.0 implementation and inductor selection
To comply with DiSEqC 2.x requirements, an output R-L filter is needed. The internal 22
kHz signal is superimposed to the VOUT DC voltage to generate the LNB output 22 kHz
tone and the LNBH25 is provided with the BPSW connected to an external transistor (refer
to Figure 13), which allows bypassing the output RL filter during the 22 kHz tone
transmission. This solution allows the 22 kHz tone to pass without any losses due to the RL filter impedance. By the way, respect to the minimum DC voltage requirement, it is
recommended to use an inductor with a current rating higher than the rated output current
and a low DRC to minimize the voltage drop.
For example:
IOUT = 500 mA
DRC=33 m (Coilcraft inductor DO3340P-224)
Equation 6:
VDROP (V) = DCR (Ω) x IOUT (A) = 0.440 x 0.5 = 0.22 V
Several inductors suitable for the LNBH25 are listed in the below table:
Table 5: Recommended inductors for output R-L filter
Supplier
Order code
ISAT (A)
DRC(m)
Mounting type
CD104-221MC
1.6
67
S.M.D
RHC110-221M
2.4
88
T.H.
822LY-221K
1.3
70
T.H.
824LY-221K
1.72
76
T.H.
A671HN-221L
2.44
21
T.H.
A814LY-221M
2.0
75
S.M.D
ELC08D221E
1.8
51
T.H.
ELC11D221E
3.2
40
T.H.
DO5010H-224
2.4
380
SMT
MSS1278-224
2.3
360
SMT
DO3340P-224
1.6
440
SMT
Sumida
Toko
Panasonic
Coilcraft
5.8
TVS diode
The LNBH25 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. Surge pulses occur due to direct or indirect
lightning strikes to an external (outdoor) circuit. This leads to currents or electromagnetic
fields causing high voltage or current transients. The LNBH25 device doesn't withstand
such high energy discharges, so transient voltage suppressor (TVS) devices are used to
protect the LNBH25 and other devices electrically connected to the antenna cable.
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Component selection guide
AN4175
Figure 15: Recommended TVS diode connection
The LNBTVS, developed by STMicroelectronics, is a dedicated lightning and electrical
overstress surge protection for LNB voltage regulators. This protection complies with the
stringent IEC61000-4-5 standard with surges up to 500 A with a whole range of products
for a cost/performance optimization.
The correct choice of the TVS diode must be taken into account according to the
maximum peak power dissipation that the diode supports.
Table 6: Recommended ST LNBTVS
Order code
VBRtyp. (V)
Ppp (W)
10/100 µs
LNBTVS4-220
23.1
1800
LNBTVS4-221
23.1
2000
LNBTVS4-222S
23.1
2000
LNBTVS6-221S
21.3
3000
Select the TVS diode, which is able to support the Ppp(W) whose value is indicated in
Table 5: "Recommended inductors for output R-L filter ".
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6
Layout guidelines
Layout guidelines
Due to high current levels and fast switching waveforms, which radiate noise, a proper PC
board layout and a star ground configuration to protect sensitive analog ground are very
important. Besides, lead lengths should be minimized to reduce stray capacitances, trace
resistance, and radiated noise. Ground noise could 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). Input bypass capacitors (C1 and C4) should be placed as
close as possible to VCC and GND and the DC-DC output capacitors (C2 and C3) as close
as possible to VUP. Excessive noise on the VCC input may falsely trigger the undervoltage
2
circuitry, resetting the I C internal registers. If this occurs, the registers are set to zero and
the LNBH25 is in shutdown mode.
6.1
PCB layout
Any switch mode power supply requires a good design of the PCB (printed circuit board)
layout in order to achieve the top of performance in terms of system functionality.
Component placing, GND trace routing and their widths are usually the major issues. Basic
rules, commonly used for DC-DC converters for a good PCB layout, should be followed. All
traces, carrying current, should be drawn on the PCB as short and thick as possible. This
should minimize resistive and inductive parasitic effects, gaining system efficiency.
Figure 16: STEVAL-CBL009V1 top layer
GIPG3007151455LM
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Layout guidelines
AN4175
Figure 17: STEVAL-CBL009V1 bottom layer
GIPG3007151457LM
Figure 18: STEVAL-CBL009V1 component layout
GIPG3007151459LM
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Layout guidelines
Figure 19: STEVAL-CBL010V1 top layer
GIPG3007151500LM
Figure 20: STEVAL-CBL010V1 bottom layer
GIPG3007151503LM
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Layout guidelines
AN4175
Figure 21: STEVAL-CBL010V1 component layout
GIPG3007151505LM
6.2
Start-up procedure
To test the board, you need:




2
I C BUS interface
LNBH25/26 testing software
Dual output power supply
Electronic load
Step 1: the LNBH25/26 testing software
2
Step 2: plug the I C connector in CN4
Step 3: supply the evaluation board with CN1
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Layout guidelines
Figure 22: PCB connector
VIN
to supply the evaluation board
(Typ. 12 V DC). Use a power supply
with 1 A clamp current or higher.
LNBOUT
to supply LNB
CN2
open drain output for IC fault
conditions
FLT tip:
CN3
ADDR tip: to determine the I 2 C
device address.
DSQIN tip: DiSEqC input acceptsDiSEqC
envelope or external 22 kHz TTL signal
input.
CN4
I2 C interface
connections :
for data transmissions
from I2C interface to the
LNBH25 and vice versa.
EXTM tip: external
modulation logic input pin
which activates the
22 kHz tone output on the
VoTX pin. Set to ground if
not used.
GIPG3007151542LM
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Revision history
7
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Revision history
Table 7: Document revision history
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Date
Revision
Changes
21-Aug-2015
1
First release.
04-Sep-2015
2
Updated pin configuration figure, the LNBH25 evaluation board
BOM list table and DC-DC converter inductor section.
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