Datasheet

The positive charge-pump regulator’s startup can be
delayed by connecting an external capacitor from
DEL2 to AGND. An internal constant-current source
begins charging the DEL2 capacitor when EN2 is logic-
high, and the step-down regulator reaches regulation.
When the DEL2 voltage exceeds V
REF
, the positive
charge-pump regulator is enabled. Each time it is
enabled, the positive charge-pump regulator goes
through a soft-start routine by ramping up its internal
reference voltage from 0 to 1.25V in 128 steps. The
soft-start period is 3ms (typ) and FBP fault detection is
disabled during this period. The soft-start feature effec-
tively limits the inrush current during startup.
Negative Charge-Pump Regulator
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 external resis-
tive voltage-divider from its output to REF with the mid-
point connected to FBN. The number of charge-pump
stages and the setting of the feedback divider determine
the output of the negative charge-pump regulator. The
charge-pump controller includes a high-side p-channel
MOSFET (P2) and a low-side n-channel MOSFET (N2) to
control the power transfer as shown in Figure 4.
During the first half cycle, P2 turns on, and flying
capacitor C13 charges to VIN minus a diode drop
(Figure 4). During the second half cycle, P2 turns off,
and N2 turns on, level shifting C13. This connects C13
in parallel with reservoir capacitor C12. If the voltage
across C12 minus a diode drop is greater than the volt-
age across C13, charge flows from C12 to C13 until the
diode (D3) turns off. The amount of charge transferred
from the output is determined by the error amplifier,
which controls N2’s on-resistance.
The negative charge-pump regulator is enabled when
EN1 is logic-high and the step-down regulator reaches
regulation. Each time it is enabled, the negative
charge-pump regulator goes through a soft-start rou-
tine by ramping down its internal reference voltage
from 1.25V to 250mV in 102 steps. The soft-start period
is 3ms (typ) and FBN fault detection is disabled during
this period. The soft-start feature effectively limits the
inrush current during startup.
MAX17113
Low-Cost, Multiple-Output
Power Supply for LCD TVs
20 ______________________________________________________________________________________
P2
N2
DRVN
CPGND
VIN
FBN
NEGATIVE CHARGE-PUMP REGULATOR
OUTPUT
REF
MAX17113
C12
C13
R2
R1
D3
REF
0.25V
OSC
ERROR
AMPLIFIER
Figure 4. Negative Charge-Pump Regulator Block Diagram