MAX1579ETG+ Maxim Integrated Products, MAX1579ETG+ Datasheet - Page 9

• Manufacturer Part Number: MAX1579ETG+
• Description: IC PS BIAS/WHITE LED TFT 24-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1579ETG+

• Applications: LCD Display
• Current - Supply: 3mA
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-TQFN Exposed Pad
• Number Of Segments: 8
• Operating Supply Voltage: 2.7 V to 5.5 V
• Maximum Power Dissipation: 1667 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX1578/MAX1579 contain an LED driver boost
converter and three charge pumps for LCD bias. The
undervoltage-lockout (UVLO) feature disables the LED
boost converter and the charge pumps when the input
voltage is below 2.35V (typ). Once V
2.35V, and V
converter and charge pumps are enabled, respectively.
The outputs of the MAX1578/MAX1579 charge pumps
are sequenced to turn on and off in a predictable fash-
ion. The turn-on sequence is as follows (Figure 1):
1) When ONBIAS is high, the MAIN regulator (5V) is
2) When V
3) When V
The turn-off sequence is as follows (Figure 2):
1) When ONBIAS is driven low, the NEG charge pump
2) Once V
3) Once V
Figure 1. Charge-Pump Turn-On Sequence
Figure 2. Charge-Pump Turn-Off Sequence
V
V
V
V
POS
V
NEG
V
POS
NEG
MAIN
enabled.
(-10V) is enabled.
(+15V) is enabled.
(-10V) is disabled.
pump (+15V) is disabled.
is disabled and discharged.
MAIN
ONBIAS
ONBIAS
(+15V)
(-10V)
(+15V)
Complete Bias and White LED Power Supplies
(-10V)
(5V)
(5V)
NEG
POS
MAIN
NEG
Charge-Pump Output Sequencing
CTRL
is discharged to -0.87V, the POS charge
falls to 0.87V, the MAIN regulator (+5V)
reaches -8V, the POS charge pump
exceeds 4.6V, the NEG charge pump
_______________________________________________________________________________________
and V
Detailed Description
ONBIAS
Bias Power and UVLO
are high, the boost
IN
rises above
The MAX1578/MAX1579 include a charge pump that
uses two external capacitors to provide +5.5V output
(V
put (MAIN). The control logic configures the pump to
switch automatically between 1.5x and 2x modes to
maximize efficiency. If V
pump stops switching. When ONBIAS is driven low,
V
A low-dropout linear regulator regulates the output of
the main charge pump to +5V at MAIN. The MAIN out-
put is capable of sourcing as much as 25mA to an
external load and also supplies the POS and NEG
charge pumps. Drive ONBIAS low to disable the MAIN,
POS, and NEG outputs. During shutdown, MAIN is dis-
charged to GND with an internal 1kΩ resistor.
The MAX1578/MAX1579 include a positive and nega-
tive charge pump for LCD bias. The POS and NEG
charge pumps are powered from V
NEG charge pumps operate at 15.6kHz with a 50%
duty cycle.
The NEG charge pump uses capacitors at CD1 and
CD2 to generate -10V (-2 x V
ic capacitors and 200Ω ±5% resistors in series between
CD1 and PMP and between CD2 and PMPB. Drive
ONBIAS high to enable MAIN, NEG, and POS. During
shutdown, the NEG output is discharged to GND with an
internal 1.5kΩ resistor.
The POS charge pump uses capacitors at CU1, CU2,
and CU3 to generate +15V (3 x V
ceramic capacitors between CU1 and PMP, between
CU2 and PMPB, and between CU3 and GND. Drive
ONBIAS high to enable MAIN, NEG, and POS. During
shutdown, POS is discharged to GND with an internal
3kΩ resistor.
LED power is supplied by an internal MOSFET, 1MHz
boost converter. The boost converter is capable of dri-
ving up to 8 series LEDs at 25mA.
The output of the boost converter is regulated to main-
tain a constant voltage at CS, and therefore a constant
current through the LEDs. Once V
the UVLO voltage (2.35V) and V
the boost converter enters soft-start and charges the
output to its regulation voltage. An overvoltage-protec-
tion circuit shuts down the boost converter if V
exceeds 34V.
for Small TFT Displays
DD
DD
is connected to IN.
) that is used to power the regulated LDO +5V out-
POS Charge Pump (+15V Supply)
NEG Charge Pump (-10V Supply)
POS/NEG Charge Pumps
LED Backlighting Power
DD
MAIN
exceeds 5.5V, the charge
MAIN Charge Pump
). Connect 1µF ceram-
CTRL
IN
MAIN
MAIN
is increased above
is above 0.17V,
). Connect 1µF
. The POS and
OUT
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