LED7706 Application information
1.
A careful PCB layout is important for proper operation. In this section some guidelines are provided in order to achieve a good layout.
2. The device has two different ground pins: signal ground (SGND) and power ground
(PGND). The PGND pin handles the switching current related to the boost section; for this reason the PCB traces should be kept as short as possible and with adequate width.
3. The signal ground is the return for the device supply and the current generators and can be connected to the thermal pad.
4. The heat dissipation area (adequate to the application conditions) should be placed backside respect to the device and with the lowest thermal impedance possible (i.e.
PCB traces in the backside should be avoided). The dissipation area is thermally and electrically connected to the thermal pad by several vias (nine vias are recommended).
5. The signal and power grounds must be connected together in a single point as close as possible to the PGND pin to reduce ground loops.
6. The R-C components of the compensation network should be placed as close as possible to the COMP pin in order to avoid noise issue and instability of the compensation.
7. Noise sensitive signals (i.e. feedbacks and compensation) should be routed as short as possible to minimize noise collection. The LED7706 pinout makes it easy to separate power components (e.g. inductor, diode) from signal ones.
8. The LX switching node should have and adequate width for high efficiency.
9. The critical power path inductor-LX-PGND must be as short as possible by mounting the inductor, the diode and COUT as close as possible each other.
10. The capacitors of the compensated divider connected to the OVSEL pin should be placed as close as possible to the OVSEL pin.
11. In order to assure good performance in terms of row current accuracy/mismatch, the
PCB traces from the rows pins to the LEDs should have similar length and width.
12. The capacitors of the filter connected to LDO5 and VIN pins should be mounted as close as possible to the mentioned pins
Figure 21
and
Figure 22 shows the demonstration board layout (top view and bottom view
respectively).
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Application information
Figure 21.
Demonstration board layout (top view)
LED7706
Figure 22.
Demonstration board layout (bottom view)
Figure 23
shows the LED7706 demonstration board application circuit, whereas Table 9
lists the used components and their value.
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LED7706
Figure 23.
LED7706 demonstration board schematic
Application information
AM00609v1
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Application information LED7706
Table 9.
Component
LED7706 demonstration board component list
Description Package Part number
C1
Ceramic, 35V
X5R, 20%
Ceramic, 50V
X7R, 20%
SMD 1210
SMD 1206
SMD 1206
UMK325BJ106KM-T
GRM31CR71H225KA88B
GRM31CR71H225KA88B
R12
R13
L1
D1
D2
D3
R5
R6
R7
R8
R9, R10
R11
C10
C11
C12
C13
R1
R2
R3
R4
C2,C3
C4
C5
C6
C7
C8
C9
U1
J2
J8
SW1, SW2
SW3
Ceramic, 25V
X5R, 20%
Chip resistor
0.1 W, 1%
Chip resistor
0.1 W, 1%
SMD 0603
SMD 0603
SMD 0603
6u8, 75 m
Ω, 2.7 A
6x6 mm
Schottky, 40 V, 1 A DO216-AA
Red LED, 3 mA
Signal Schottky
SMD 0603
SOD-523
QFN4x4 Integrated circuit
PCB pad jumper
Header 8
Jumper 3
Push button
SIL 8
SIL 3
6x6 mm
LPS6235-682MLC
STPS1L40M
LED7706
FSM4JSMAT
MFR Value
Taiyo Yuden
Murata
Standard
Standard
Standard
Coilcraft
ST
Standard
BAS69
ST
10 µF
2.2 µF
N.M.
1 µF
100 nF
3.3 nF
4.7 nF
N.M.
220 pF
4.7 nF
N.M.
15 pF
510 k
Ω
16 k
Ω
2.4 k
Ω
4.7
Ω
330 k
Ω
51 k
Ω
180 k
Ω
680 k
Ω
100 k
Ω
1.2 k
Ω
N.M.
N.M.
6.8 µF
STPS1L40M
N.M.
LED7706
Standard
Standard
TYCO
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