THV6531 Datasheet, PDF (6/11 Pages) THine Electronics, Inc. – THV6531 is a controller IC power supply system with

THL6531_Rev.1.01_E
Function
Boost converter
The LCD panel VLS supply is generated from a
high-efficiency PWM boost converter operating with
current mode control, and the switching frequency is
1.2MHz. During the on-period, T_ON, the synchronous
FET connects one end of the inductor to ground,
therefore increasing the inductor current. After the FET
turns off, the inductor switching node, LX, is charged to
a positive voltage by the inductor current. The
freewheeling diode turns on and the inductor current
flows to the output capacitor.
The converter operates in continuous conduction mode
when the load current I_VLS is at least one-half of the
inductor ripple current ΔI_rip.
I _IN  ^{I rip}
2
I _rip

(VLS  V_IN ) V_IN
L  F_OSC VLS
The output voltage (VLS) is determined by the duty
cycle(D) of the power FET on-time and the input
voltage, V_IN.
VLS  ^VIN
1 D
The average load current, I_VLS, can be calculated from
the power conservation law.
 V_IN I _IN VLS  I_VSL
where η is the power conversion efficiency. For a lower
load current, the inductor current would decay to zero
during the free-wheeling period and the output node
would be disconnected from the inductor for the
remaining portion of the switching period. The converter
would operate in the discontinuous conduction mode .
Current mode control is well known for its robustness
and fast transient response. An inner current feedback
loop sets the on-time and the duty cycle such that the
current through the inductor equals to the current
computed by the compensator. This loop acts within one
switching cycle. A slope compensation ramp is added to
suppress sub-harmonic oscillations. An outer voltage
feedback loop subtracts the voltage on the FB pin from
the internal reference voltage and feeds the difference to
the compensator operational transconductance amplifier.
This amplifier is compensated by an external R-C
network to allow the user to optimize the transient
response and loop stability for the specific application
conditions.
The output voltage VLS can be set by external resistor
divider R1 and R2 connected to FB.
VLS

V_FB


^1

R₁
R₂



VLS
LX
R1
FB
R2
Fig. 1 FB setup
[Compensator selection]
This current mode boost converter has a current sense
loop and a voltage feedback loop. The current sense
loop does not need any compensation. The voltage
feedback loop is compensated by an external series
R-C network R_PC and C_PC from PC pin to ground.
RCOMP is set to define the high frequency integrator gain
for loop bandwidth which relates to the transient
response. C_PC is set to ensure the loop stability.
[Output capacitor selection]
The output voltage ripple due to converter switching is
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