MAX8753ETI-T Maxim Integrated, MAX8753ETI-T Datasheet - Page 14

• Manufacturer Part Number: MAX8753ETI-T
• Description: LCD Drivers
• Manufacturer: Maxim Integrated

TFT LCD DC-DC Converter with
Integrated Charge Pumps
Figure 5. Negative Charge-Pump Regulator Block Diagram
The MAX8753 contains a linear regulator that uses an
internal pMOS transistor to supply load currents up to
300mA. Connect FBL to GND to set the linear regulator
output to 2.5V. Connect an external resistive voltage-
divider between the regulator output and GND with the
midpoint connected to FBL to adjust the linear-regulator
output. An error amplifier compares the FBL voltage with
the 1.25V internal reference voltage and amplifies the
difference. If the feedback voltage is higher than the ref-
erence voltage, the controller lowers the gate voltage of
the pMOS transistor, which reduces the amount of cur-
rent delivered to the output. If the feedback voltage is
too low, the device increases the pMOS transistor’s gate
voltage, which allows more current to pass to the output
and raises the output voltage. The linear regulator also
includes an output current limit that protects the internal
pass transistor against short circuits.
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CONTROL
CHARGE-
LOGIC
PUMP
OSC
R
ON
MAX8753
Linear Regulator
EA
1.25V
GND
250mV
The linear regulator is enabled whenever REF is in reg-
ulation and SHDN is logic-high.
The linear regulator current-limit circuitry monitors the
current flowing through the internal pass transistor. The
internal current limit is approximately 500mA. The linear
regulator output declines when it is not able to supply
the load current. If the FBL voltage drops below 0.75V,
the current limit folds back to approximately 100mA.
The reference output is nominally 1.25V and can
source up to 50µA. Bypass REF with a 0.22µF ceramic
capacitor connected between REF and GND. The refer-
ence remains disabled in shutdown.
Power-Up Sequence and Shutdown Control
When the MAX8753 is powered up, all outputs are dis-
abled as long as SHDN is low. After SHDN is logic-
high, the reference and the linear regulator power up
first. The main DC-DC step-up converter, the negative
PGND
SUPN
REF
P3
C3P
N3
FBN
C3
D4
D5
R4
C
REF
Reference Voltage (REF)
R3
V
V
SUPN
NEG
C
NEG