Datasheet

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APPLICATION INFORMATION
OUTPUT POWER CAPABILITY
GHGHGH
IVP ×=
GLGLGL
IVP ×=
5.0VVforI
0.5V
V
PP
MAININMAIN
MAIN
MAIN
MAIN_LDOMAINBOOT
2
+<×
+
≈η×=
MAININMAIN
IN
MAIN
MAIN_LDOMAINBOOT
VVforI
V
V
PP
2
>×≈η×=
SETTING THE OUTPUT VOLTAGE
FBMMAIN
R6
R6R5
VV
+
×=
FBHGH
R2
R2R1
VV
+
×=
MAINGL
R4
R3
VV ×=
TPS65120, TPS65121, TPS65123, TPS65124
SLVS531A – JUNE 2004 – REVISED MARCH 2005
The first step in the design procedure is to calculate the maximum output current for each output under certain
input and output voltage conditions. The TPS6512x uses time-multiplex operation to share the inductive storage
element between BOOT, VGH and VGL outputs. To avoid complex calculations it is recommended to use the
specified output-power data from the electrical characteristics table to determine the maximum output-power
capability.
The following example shows how to proceed for given requirements:
• Input Voltage = 3.0 V
• MAIN Output = 5.0 V @ 10 mA
• VGH output = 12 V @ 500 µA
• VGL output = -12 V @ 300 µA
1. Calculate Maximum Output Power on VGH Output
2. Calculate Maximum Output Power on VGL Output
3. Calculate Maximum Output Power on BOOT Output
4. Maximum Output Power Verification
The electrical characteristics table states that for V
IN
> 3.0 V, the maximum power on VGH and VGL outputs
must be lower than 35 mW each. Furthermore, the total output power (P
BOOT
+ P
GH
+ P
GL
) must be lower than
150 mW.
In our design example, P
GH
= 6 mW, P
GL
= 3.6 mW, and P
BOOT
= 55 mW. Since these numbers are well below
the specified values, we can conclude that TPS6512x can reasonably power such a display.
The output voltages are defined as shown in Figure 22 .
with an internal reference voltage V
FBM
typical = 1.213V.
with an internal reference voltage V
FBH
typical = 1.213V.
To minimize the operating quiescent current, set R2, R4 and R6 in the range 100 k Ω to 300 k Ω . Great care
should be taken to route the FBx lines away from noise sources such as the inductor or the SWN and SWP lines.
A feed-forward capacitor across the upper feedback resistor (R1, R3) on VGH and VGL outputs can be used to
provide more overdrive for the error comparator. This feed-forward capacitor helps to reduce the output ripple
voltage. A good starting value is 10 pF.
17