MAX8751ETJ+ Maxim Integrated Products, MAX8751ETJ+ Datasheet - Page 19

• Manufacturer Part Number: MAX8751ETJ+
• Description: IC CNTRLR CCFL INV 32-TQFN
• Manufacturer: Maxim Integrated Products
• Type: CCFL Controllerr

Specifications of MAX8751ETJ+

• Frequency: 30 ~ 80 kHz
• Current - Supply: 3.2mA
• Voltage - Supply: 6 V ~ 28 V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 32-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Lead Free Status / Rohs Status: Details

Table 1. Phase-Shift Setting
The internal linear regulator steps down the DC input
voltage to 5.3V (typ). The linear regulator supplies
power to the internal control circuitry of the MAX8751.
V
drops to 4.5V in shutdown.
The MAX8751 includes an undervoltage lockout
(UVLO) circuit. The UVLO circuit monitors the V
age. When V
ables both high-side and low-side gate drivers and
resets the fault latch.
When the MAX8751 is placed in shutdown, all functions
of the IC are turned off except for the 5.3V linear regu-
lator. In shutdown, the linear regulator output voltage
drops to about 4.5V and the supply current is 6µA (typ).
While in shutdown, the fault latch is reset. The device
can be placed into shutdown by pulling SHDN to its
logic low level.
The MAX8751 requires four external n-channel power
MOSFETs to form a full-bridge inverter circuit to drive
the transformer primary. Since the positive half-cycle
and negative half-cycle are symmetrical, the same type
of MOSFET should be used for the high-side and low-
side switches. When selecting the MOSFET, focus on
the voltage rating, current rating, on-resistance
(R
Select a MOSFET with a voltage rating at least 25%
higher than the maximum input voltage of the inverter.
For example, if the maximum input voltage is 24V, the
X = Don’t care.
CC
DS(ON)
GND
GND
powers the MOSFET gate drivers. The V
PS2
V
V
X
CC
CC
PIN SETTING
), total gate charge, and power dissipation.
CC
Applications Information
Linear Regulator Output (V
is below 4.2V (typ), the MAX8751 dis-
______________________________________________________________________________________
GND
GND
PS1
V
V
X
CC
CC
Low-Power Shutdown
MASTER
Fixed-Frequency, Full-Bridge CCFL
0
0
0
0
0
MOSFETs
SLAVE 1
CC
N/A
180
120
90
72
CC
UVLO
voltage
PHASE SHIFT IN DEGREES
CC
volt-
)
SLAVE 2
voltage rating of the MOSFET should be 30V or higher.
The current rating of the MOSFET should be higher
than the peak primary current at the minimum input
voltage and full brightness. Use the following equation
to estimate the primary peak current I
where P
V
mated efficiency at the minimum input voltage.
Assuming the full bridge drives four CCFLs and the
maximum output power of each lamp is 4.5W, the total
maximum output power is 18W. If the minimum input
voltage is 8V and the estimated efficiency is 75% at
that input, the peak primary current is approximately
4.3A. Therefore, power MOSFETs with a DC current rat-
ing of 5A or greater are sufficient.
Since the regulator senses the on-state, drain-to-source
voltage of both MOSFETs to detect the transformer prima-
ry current, the lower the MOSFET R
current limit is. Therefore, the user should select n-chan-
nel MOSFETs with low R
loss, and keep the primary current limit at a reasonable
level. Use the following equation to estimate the maxi-
mum and minimum values of the primary current limit:
N/A
N/A
240
180
144
IN
_
MIN
is the minimum input voltage, and is the esti-
OUT
Inverter Controller
SLAVE 3
I
_
PEAK_PRI
N/A
N/A
N/A
270
216
MAX
is the maximum output power,
=
DS(ON)
SLAVE 4
2 xP
V
N/A
N/A
N/A
288
NA
IN_MIN
OUT_MAX
to minimize conduction
DS(ON)
x
PEAK
η
, the higher the
PHASES
_
NO. OF
PRI
1
2
3
4
5
:
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