ISL78010 Datasheet, PDF (8/18 Pages) Intersil Corporation – Automotive Grade TFT-LCD Power Supply

ISL78010
Applications Information
The ISL78010 provide a highly integrated multiple output
power solution for TFT-LCD automotive applications. The
system consists of one high efficiency boost converter and
three linear-regulator controllers (V_ON, V_OFF, and V_LOGIC)
with multiple protection functions. A block diagram is shown
in Figure 20. Table 1 lists the recommended components.
The ISL78010 integrates an N-Channel MOSFET boost
converter to minimize external component count and cost.
The A_VDD, V_ON, V_OFF, and V_LOGIC output voltages are
independently set using external resistors. V_ON, V_OFF
voltages require external charge pumps which are post
regulated using the integrated LDO controllers.
TABLE 1. RECOMMENDED TYPICAL APPLICATION
DIAGRAM COMPONENTS
DESIGNATION
DESCRIPTION
C₁, C₂, C₃
10µF, 16V X7R ceramic capacitor (1206)
TDK C3216X7RIC106M
C₂₀, C₃₁
4.7µF, 25V X5R ceramic capacitor (1206)
TDK C3216X5R1A475K
D₁
1A, 20V low leakage Schottky rectifier (CASE
457-04) ON SEMI MBRM120ET3
D₁₁, D₁₂, D₂₁ 200mA, 30V Schottky barrier diode (SOT-23)
Fairchild BAT54S
L₁
6.8µH, 1.3A Inductor
TDK SLF6025T-6R8M1R3-PF
Q₁
-2.4, -20V P-Channel 1.8V specified
PowerTrench MOSFET (SuperSOT-3)
Fairchild FDN304P
Q₂
200mA, 40V NPN amplifier (SOT-23)
Fairchild MMBT3904
Q₃
200mA, 40V PNP amplifier (SOT-23)
Fairchild MMBT3906
Q₄
-2A, -30V single P-Channel logic level
PowerTrench MOSFET (SuperSOT-3)
Fairchild FDN360P
Q₅
1A, 30V PNP low saturation amplifier (SOT-23)
Fairchild FMMT549
Boost Converter
The main boost converter is a current mode PWM converter
at a fixed frequency of 1MHz, which enables the use of low
profile inductors and multi-layer ceramic capacitors. This
results in a compact, low cost power system for LCD panel
design.
The ISL78010 is designed for continuous current mode, but
it can also operate in discontinuous current mode at light
load. In continuous current mode, current flows continuously
in the inductor during the entire switching cycle in steady
state operation. The voltage conversion ratio in continuous
current mode is given by Equation 1:
A_{-----V----D----D--}
V_IN
=
------¹-------
1–D
(EQ. 1)
where D is the duty cycle of the switching MOSFET.
Figure 21 shows the block diagram of the boost regulator. It
uses a summing amplifier architecture consisting of GM
stages for voltage feedback, current feedback and slope
compensation. A comparator looks at the peak inductor
current cycle by cycle and terminates the PWM cycle if the
current limit is reached.
An external resistor divider is required to divide the output
voltage down to the nominal reference voltage. Current
drawn by the resistor network should be limited to maintain
the overall converter efficiency. The maximum value of the
resistor network is limited by the feedback input bias current
and the potential for noise being coupled into the feedback
pin. A resistor network in the order of 60kΩ is recommended.
The boost converter output voltage is determined by
Equation 2:
A_VDD
=
R_{-----1----+-----}R_-----2-
R₁
×
V_REF
(EQ. 2)
The current through the MOSFET is limited to 2A peak. This
restricts the maximum output current based on Equation 3:
I_OMAX
=
⎛
⎝
I_L
MT
–
-^Δ--₂--^I--^L-_⎠⎞
×
V_-----I--N--
V_O
(EQ. 3)
Where ΔIL is peak to peak inductor ripple current, and is set
by Equation 4:
ΔI_L
=
-^V----^I--^N-- × -^D---
L f_S
(EQ. 4)
where f_S is the switching frequency.
8
FN6501.0
May 30, 2007