MAX16928_12 Datasheet, PDF (17/20 Pages) Maxim Integrated Products – Automotive TFT-LCD Power Supply with Boost Converter and Gate Voltage Regulators

MAX16928
Automotive TFT-LCD Power Supply with Boost
Converter and Gate Voltage Regulators
The voltage and current rise and fall times at the LXP
node are equal to t_R-V (voltage rise time), t_F-V (voltage fall
time), t_R-I (current rise time), and t_F-I (current fall time),
and are determined as follows:
t _R-V
=
V_SH
+
V_SCHOTTKY
K _R-V
t _F-V
=
V_SH
+
V_SCHOTTKY
K _F-V
t
R-I
=
I_IN(DC,MAX)
K _R-I
t
F-I
=
I_IN(DC,MAX)
K _F-I
K_R-V, K_F-V, K_R-I, and K_F-I are the voltage and current
slew rates of the LXP node and are supply dependent.
Use Table 4 to determine their values.
Positive-Gate Voltage Regulator
Use the lowest number of charge-pump stages possible
in supplying power to the positive voltage regulator.
Doing so minimizes the drain-source voltage of the inte-
grated pMOS switch and power dissipation. The power
dissipated in the switch is given as:
P_GH = (V_CP - V_GH) × I_{LOAD(MAX)_GH}
Ensure that the voltage on CP does not exceed the
CP overvoltage threshold as given in the Electrical
Characteristics table.
Negative-Gate Voltage Regulator
Use the lowest number of charge-pump stages possible
to provide the negative voltage to the negative-gate
voltage regulator. Estimate the power dissipated in the
negative-gate voltage regulator using the following:
P_GL = (V_INA + |V_CN| - V_BE) × I_DRVN
where V_BE is the base-emitter voltage of the external npn
bipolar transistor, and I_DRVN is the current sourced from
DRVN to the R_BE bias resistor and to the base of the
transistor, which is given by:
I_DRVN
= ^VBE
R_BE
+
I_GL
h _FE +1
1.8V/3.3V Regulator Controller
The power dissipated in the 1.8V/3.3V regulator controller
is given by:
P_REG = (V_INA - V_{OUT_REG} - V_BE) × I_DR
where V_{OUT_REG} = 1.8V or 3.3V, V_BE is the base-emitter
voltage of the external npn bipolar transistor, and I_DR is
the current sourced from DR to the base of the transistor.
I_DR is given by:
I_DR
=
I_LOAD
h_FE + 1
where I_LOAD is load current of the 1.8V/3.3V regulator
controller, and h_FE is the current gain of the transistor.
Total Power Dissipation
The total power dissipated in the package is the sum of
the losses previously calculated. Therefore, total power
dissipation can be estimated as follows:
P_T = P_LXP + P_GH + P_GL + P_REG
Achieve maximum heat transfer by connecting the
exposed pad to a thermal landing pad and connecting
the thermal landing pad to a large ground plane through
thermal vias.
Table 4. LXP Voltage and Current Slew Rates vs. Supply Voltage
V_INA (V)
3.3
5
RISING VOLTAGE
SLEW RATE,
K_R-V (V/ns)
0.52
1.35
LXP VOLTAGE AND CURRENT SLEW RATES
FALLING VOLTAGE
SLEW RATE,
K_F-V (V/ns)
1.7
2
RISING CURRENT
SLEW RATE,
K_R-I (A/ns)
0.13
0.3
FALLING CURRENT
SLEW RATE,
K_F-I (A/ns)
0.38
0.44
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