MAX8753ETI-T Maxim Integrated, MAX8753ETI-T Datasheet - Page 13

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

C2. If the voltage across C2 plus a diode drop (V
V
capacitor voltage (V
to C2 until diode D2 turns off. Similarly, when CLKB
becomes high, C2 is also level shifted by V
This connects C2 in parallel with the reservoir capacitor
C
(V
ed flying capacitor voltage (V
from C2 to C
The negative charge-pump regulator is typically used
to generate the negative supply rail for the TFT LCD
gate-driver ICs. The output voltage is set with an exter-
nal resistive voltage-divider from its output to REF with
the midpoint connected to FBN. The number of charge-
pump stages and the setting of the feedback divider
determine the output of the negative charge-pump reg-
ulator. The charge-pump controller includes a high-side
Figure 4. Positive Charge-Pump Regulator Block Diagram
DIODE
POS
POS
V
SUPP
C1
C2
. If the voltage across C
+ V
) is smaller than the first level-shifted flying
C1N
C1P
C2P
C2N
SUPP
DIODE
CONTROL
Negative Charge-Pump Regulator
POS
R
ON
MAX8753
CTRL
) is smaller than the second level-shift-
until diode D3 turns off.
______________________________________________________________________________________
C1
+ V
SUPP
CLK
C2
POS
), charge flows from C1
+ V
SUPP
plus a diode drop
), charge flows
TFT LCD DC-DC Converter with
P1
N1
SUPP
C1N
CHARGE-
LOGIC
PUMP
volts.
C2
D1
Integrated Charge Pumps
+
D2
D3
p-channel MOSFET (P3) and a low-side n-channel
MOSFET (N3) to control the power transfer as shown in
Figure 5. The negative charge pump can also be con-
figured as a multiple-stage charge pump. The required
number of stages (n
the desired negative output voltage. Figure 1 gives an
example with a two-stage negative charge pump.
In Figure 5, during the first half-cycle, the p-channel
MOSFET turns on and flying capacitor C3 charges to
V
cycle, the p-channel MOSFET turns off, and the n-chan-
nel MOSFET turns on, level shifting C3. This connects
C3 in parallel with the reservoir capacitor C
voltage across C3 minus a diode drop is lower than the
voltage across C
until the diode turns off. The amount of charge trans-
ferred to the output is controlled by the variable n-chan-
nel on-resistance.
C2N
N2
SUPN
P2
OSC
minus a diode drop. During the second half-
THRESHOLD
SUPP OV
EA
NEG
neg
, charge flows from C3 to C
) is determined by V
R1
CLK
REF
REF
CONTROL
R2
R
ON
EA
OUTP
FBP
NEG
R5
R6
SUPN
. If the
V
C
POS
POS
NEG
and
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