MAX16928CGUP/V+T Maxim Integrated, MAX16928CGUP/V+T Datasheet - Page 11

• Manufacturer Part Number: MAX16928CGUP/V+T
• Description: LCD Drivers Automotive TFT Power Supply
• Manufacturer: Maxim Integrated

Specifications of MAX16928CGUP/V+T

• Rohs: yes

The positive-gate voltage regulator includes a p-channel
FET output stage to generate a regulated output between
5V and (V
wide line and load conditions. It is capable of at least
20mA of output current and includes current-limit protec-
tion. V
drivers’ gate-on voltage.
The regulator derives its positive supply voltage from a
noninverting charge pump, a single-stage example of
which is shown in the
voltage using a multistage charge pump is possible, as
described in the
The negative-gate voltage regulator is an analog gain
block with an open-drain p-channel output. It drives an
external npn pass transistor with a 6.8kI base-to-emitter
resistor (see the
guaranteed base drive source current is at least 2mA.
V
ers’ gate-off voltage.
The output of the negative-gate voltage regulator (i.e.,
the collector of the external npn pass transistor) has load-
dependent bypassing requirements. Connect a ceramic
capacitor between the collector and ground with the
value shown in
The regulator derives its negative supply voltage from an
inverting charge pump, a single-stage example of which
is shown in the
voltage using a multistage charge pump is possible, as
described in the
The external npn transistor is not short-circuit protected.
To maintain proper pulldown capability of the external npn
transistor and optimal regulation, a minimum load of at least
500FA is recommended on the output of the GL regulator.
Table 1. Supply Sequencing
Maxim Integrated
GL
ENP
is typically used to provide the TFT-LCD gate driv-
CONTROL INPUTS
0
1
1
GH
Negative-Gate Voltage Regulator (GL)
Positive-Gate Voltage Regulator (GH)
CP
is typically used to provide the TFT-LCD gate
Automotive TFT-LCD Power Supply with Boost
- 2V). The regulator maintains accuracy over
Typical Operating
Table
Charge Pumps
Charge Pumps
Pass Transistor Selection
SEQ
X
0
1
3.
Typical Operating
Converter and Gate Voltage Regulators
section.
section.
Circuit. A more negative
Circuit. A higher
FIRST
V
V
SH
SH
section). Its
Use the enable input (ENP) to enable and disable the
boost section of the device. Connect ENP to INA for
normal operation and to GND to place the device in shut-
down. In shutdown, the INA supply current is reduced to
0.5FA.
When enabled, the boost output ramps up from V
its set voltage. Once the boost output reaches 85% of the
set voltage and the soft-start timer expires, the gate volt-
age regulators turn on in the order shown in
1.8V/3.3V regulator controller is enabled at the beginning
of the boost converter’s soft-start.
Both gate voltage regulators have a 7.45ms soft-start
time. The second one turns on as soon as the output of
the first reaches 85% of its set voltage.
Internal thermal shutdown circuitry shuts down the
device immediately when the die temperature exceeds
+165NC. A 15NC thermal shutdown hysteresis prevents
the device from resuming normal operation until the die
temperature falls below +150NC.
Three key inductor parameters must be specified for
operation with the device: inductance value (L), inductor
saturation current (I
determine the inductance value, select the ratio of inductor
peak-to-peak ripple current to average output current (LIR)
first. For LIR values that are too high, the RMS currents are
high, and therefore, I
inductors to achieve low LIR values. Typically, inductance
is proportional to resistance for a given package type,
SUPPLY SEQUENCING
Device is in shutdown
Soft-Start and Supply Sequencing (SEQ)
SECOND
V
V
GH
GL
SAT
2
R losses are high. Use high-valued
), and DC resistance (R
Design Procedure
MAX16928
Thermal Shutdown
Boost Converter
Inductor Selection
THIRD
V
Enable (ENP)
V
GH
GL
Table
DC
1. The
INA
). To
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