MAX1518BETJ+T Maxim Integrated Products, MAX1518BETJ+T Datasheet - Page 16

• Manufacturer Part Number: MAX1518BETJ+T
• Description: IC DC-DC CONV TFT-LCD 32-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1518BETJ+T

• Applications: Converter, TFT, LCD
• Voltage - Input: 2.6 ~ 6.5 V
• Number Of Outputs: 1
• Voltage - Output: 2.6 ~ 13 V
• Operating Temperature: -40°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The undervoltage-lockout (UVLO) circuit compares the
input voltage at IN with the UVLO threshold (2.5V rising,
2.30V falling, typ) to ensure the input voltage is high
enough for reliable operation. The 200mV (typ) hysteresis
prevents supply transients from causing a restart. Once
the input voltage exceeds the UVLO rising threshold,
startup begins. When the input voltage falls below the
UVLO falling threshold, the controller turns off the main
step-up regulator, turns off the linear-regulator outputs,
and disables the switch control block; the operational-
amplifier outputs are high impedance.
The reference output is nominally 1.25V and can
source at least 50µA (see the Typical Operating
Characteristics). Bypass REF with a 0.22µF ceramic
capacitor connected between REF and AGND.
Once the voltage on IN exceeds approximately 1.7V,
the reference turns on. With a 0.22µF REF bypass
capacitor, the reference reaches its regulation voltage
of 1.25V in approximately 1ms. When the reference
voltage exceeds 1.0V, the ICs enable the main step-up
regulator, the gate-on linear-regulator controller, and
the gate-off linear-regulator controller simultaneously.
The IC employs soft-start for each regulator to minimize
inrush current and voltage overshoot and to ensure a
well-defined startup behavior. During the soft-start, the
main step-up regulator directly limits the peak inductor
current. The current-limit level is increased through the
soft-start period from zero up to the full current-limit
value in eight equal current steps (ILIM / 8). The maxi-
mum load current is available after the output voltage
reaches regulation (which terminates soft-start), or after
the soft-start timer expires. Both linear-regulator con-
trollers use a 7-bit soft-start DAC. For the gate-on linear
regulator, the DAC output is stepped in 128 steps from
zero up to the reference voltage. For the gate-off linear
regulator, the DAC output steps from the reference
down to 250mV in 128 steps. The soft-start duration is
14ms (typ) for all three regulators.
A capacitor (C
switch-control-block startup delay. After the input volt-
age exceeds the UVLO threshold (2.5V typ) and the
soft-start routine for each regulator is complete and
there is no fault detected, a 5µA current source starts
charging C
TFT-LCD DC-DC Converter with
Operational Amplifiers
16
______________________________________________________________________________________
Power-Up Sequence and Soft-Start
DEL
DEL
. Once the capacitor voltage exceeds
Undervoltage Lockout (UVLO)
) from DEL to AGND determines the
Reference Voltage (REF)
1.25V (typ), the switch-control block is enabled as
shown in Figure 6. After the switch-control block is
enabled, COM can be connected to SRC or DRN
through the internal p-channel switches, depending
upon the state of CTL. Before startup and when IN is
less than V
to discharge C
using the following equation:
The switch-control input (CTL) is not activated until all
four of the following conditions are satisfied: the input
voltage exceeds V
regulators is complete, there is no fault condition detect-
ed, and V
vated and if CTL is high, the 5Ω internal p-channel
switch (Q1) between COM and SRC turns on and the
30Ω p-channel switch (Q2) between DRN and COM
turns off. If CTL is low, Q1 turns off and Q2 turns on.
Figure 6. Power-Up Sequence
VOLTAGE
INPUT
OK
2.5V
BEGINS
START
SOFT-
DEL
UVLO
12ms
1.05V
START
C
SOFT-
ENDS
exceeds its turn-on threshold. Once acti-
DEL
DEL
, DEL is internally connected to AGND
UVLO
. Select C
=
DELAY TIME
, the soft-start routine of all the
Switch-Control Block
_
DEL
CONTROL
ENABLED
SWITCH
to set the delay time
1.25V
×
1 25
5
.
µ
A
V
V
V
V
V
V
V
IN
REF
MAIN
GON
GOFF
DEL