TPS65642A Datasheet, PDF (27/77 Pages) Texas Instruments – LCD Bias With Integrated Gamma Reference for Notebook PCs, Tablet PCs and Monitors

TPS65642A
www.ti.com
SLVSC21 – OCTOBER 2013
5.1 BOOST CONVERTER 1 (AV_DD)
Boost converter 1 is synchronous and uses a virtual current mode topology that:
• Achieves high efficiencies
• Allows the converter to work in continuous-conduction mode under all operating conditions, which
simplifies compensation
• Provides a better drive signal for the negative charge pump connected to the switch node (because the
converter always runs in continuous-conduction mode, even at low output currents)
• Provides true input-output isolation when the boost converter is disabled
V_IN
AVDD
VIN
SW1
Q1B
AVDD
AV_DD
AVDD
V_REF
+
–
FREQ
Q1A
PWM
Control
SMODE
&
Q2
UVLO
GND
COMP
Figure 5-2. Boost Converter 1 Internal Block Diagram
5.1.1 Switching Frequency (Boost Converter 1)
The nominal switching frequency of boost converter 1 can be programmed to 750 kHz or 1200 kHz using
the FREQ bit in the MISC register. The factory default value is 1200 kHz.
5.1.2 Compensation (Boost Converter 1)
Boost converter 1 uses an external compensation network connected to the COMP pin to stabilize its
feedback loop. A simple series R-C network connected between the COMP pin and ground is sufficient to
achieve good performance, in effect, stable and with good transient response. Good starting values, which
will work for most applications, are 100 kΩ and 1 nF for 1200 MHz AV_DD switching frequency and 56 kΩ
and 1.5 nF for 750 kHz AV_DD switching frequency.
In some applications (for example, those using electrolytic output capacitors), it may be necessary to
include a second compensation capacitor between the COMP pin and ground. This has the effect of
adding an additional pole in the frequency response of the feedback loop, which cancels the zero
introduced by the ESR of the output capacitor.
Copyright © 2013, Texas Instruments Incorporated
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