MAX17062 Maxim Integrated Products, MAX17062 Datasheet - Page 11

• Manufacturer Part Number: MAX17062
• Description: TFT-LCD Step-Up DC-DC Converter
• Manufacturer: Maxim Integrated Products

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Figure 3. Multiple-Output TFT-LCD Power Supply
Figure 3 shows a power supply for active-matrix TFT-
LCD flat-panel displays. Output-voltage transient perfor-
mance is a function of the load characteristic. Add or
remove output capacitance (and recalculate compensa-
tion-network component values) as necessary to meet
the required transient performance. Regulation perfor-
mance for secondary outputs (VGON and VGOFF)
depends on the load characteristics of all three outputs.
Careful PCB layout is important for proper operation. Use
the following guidelines for good PCB layout:
1) Minimize the area of high-current loops by placing
Multiple-Output Power Supply for TFT LCD
the inductor, rectifier diode, and output capacitors
near the input capacitors and near the LX and
PGND pins. The high-current output loop goes from
the positive terminal of the input capacitor to the
inductor, to the IC’s LX pin, out of GND, and to the
input capacitor’s negative terminal. The high-cur-
rent output loop is from LX switch node to the recti-
fier diode (D1) to the output capacitors, and
4.5V TO 5.5V
V
IN
4.7μF
______________________________________________________________________________________
10V
C1
PCB Layout and Grounding
VGOFF
4.7μF
-15V
10V
C2
0.22μF
TFT-LCD Step-Up DC-DC Converter
C11
1μF
10Ω
C3
R5
33nF
100kΩ
R1
C4
10
8
3
9
IN
SHDN
FREQ
SS
560pF
47kΩ
MAX17062
1
2
C5
R2
2.7μH
COMP
U1
1
L1
D2
3
PGND
PGND
AGND
2) Create a power ground island (PGND) consisting of
0.1μF
C12
LX
LX
FB
reconnecting negative terminals of output capaci-
tors to PGND of the IC. This loop has very high
di/dt, and it is critical to minimize the area of this
loop. Connect these loop components with short,
wide connections. Avoid using vias in the high-cur-
rent paths. If vias are unavoidable, use many vias in
parallel to reduce resistance and inductance.
the input and output capacitor grounds and PGND
pins. Connect all these together with short, wide
traces or a small ground plane. Maximizing the
width of the power ground traces improves efficien-
cy and reduces output voltage ripple and noise
spikes. Create an analog ground plane (AGND)
consisting of the feedback-divider ground connec-
tion, the COMP and SS capacitor ground connec-
tions, and the device’s exposed backside pad.
Connect the AGND and PGND islands by connect-
ing the PGND pins directly to the exposed backside
pad. Make no other connections between these
separate ground planes.
6
7
5
4
2
EP
C6
OPEN
0.1μF
C14
D1
3
D3
R4
221kΩ
R3
20kΩ
10μF
25V
C7
2
1
0.22μF
10μF
25V
C15
C8
V
+15V/600mA
VGON
+29V
OUT
11