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| 型号： | MAX8739ETP+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 13/19页 |
| 文件大小： | 0K |
| 描述： | IC DC/DC CONV W/OPAMP 20TQFN-EP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 应用： | 转换器，TFT，LCD |
| 输入电压： | 1.8 V ~ 5.5 V |
| 输出数： | 1 |
| 输出电压： | 1.8 V ~ 13 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-WQFN 裸露焊盘 |
| 供应商设备封装： | 20-TQFN-EP（5x5） |
| 包装： | 带卷 (TR) |
TFT, LCD, DC-DC Converter with
Operational Amplifiers
Table 2. Component Suppliers
SUPPLIER
Fairchild
Sumida
TDK
Toshiba
PHONE
408-822-2000
847-545-6700
847-803-6100
949-455-2000
FAX
408-822-2102
847-545-6720
847-390-4405
949-859-3963
WEBSITE
www.fairchildsemi.com
www.sumida.com
www.component.tdk.com
www.toshiba.com/taec
inrush current. The output voltage can be set from V IN
to 13V with an external resistive voltage-divider.
The regulator controls the output voltage and the power
delivered to the output by modulating the duty cycle (D)
of the internal power MOSFET in each switching cycle.
The duty cycle of the MOSFET is approximated by:
CLOCK
LOGIC AND
DRIVER
ILIM
LX
PGND
COMPARATOR
D ≈
V MAIN ? V IN
V MAIN
SOFT-
START
I LIMIT
Figure 3 shows the block diagram of the step-up regu-
SLOPE COMP
SS
lator. An error amplifier compares the signal at FB to
1.24V and changes the COMP output. The voltage at
COMP determines the current trip point each time the
OSCILLATOR
PWM
COMPARATOR
∑
CURRENT
SENSE
internal MOSFET turns on. As the load varies, the error
amplifier sources or sinks current to the COMP output
FAULT
COMPARATOR
accordingly to produce the inductor peak current nec-
essary to service the load. To maintain stability at high
TO FAULT LOGIC
1.0V
ERROR AMP
FB
duty cycles, a slope compensation signal is summed
with the current-sense signal.
On the rising edge of the internal clock, the controller
sets a flip-flop, turning on the n-channel MOSFET and
applying the input voltage across the inductor. The cur-
rent through the inductor ramps up linearly, storing
energy in its magnetic field. Once the sum of the cur-
rent-feedback signal and the slope compensation
exceed the COMP voltage, the controller resets the flip-
flop and turns off the MOSFET. Since the inductor cur-
rent is continuous, a transverse potential develops
across the inductor that turns on the diode (D1). The
voltage across the inductor then becomes the differ-
ence between the output voltage and the input voltage.
This discharge condition forces the current through the
inductor to ramp back down, transferring the energy
stored in the magnetic field to the output capacitor and
the load. The MOSFET remains off for the rest of the
clock cycle.
Operational Amplifiers
The MAX8739 has two operational amplifiers that are
typically used to drive the LCD backplane (VCOM)
and/or the gamma-correction-divider string. The opera-
tional amplifiers feature ± 150mA output short-circuit
current, 7.5V/μs slew rate, and 12MHz bandwidth. The
1.24V
COMP
FREQ
Figure 3. Step-Up Regulator Block Diagram
rail-to-rail input and output capability maximize system
flexibility.
Short-Circuit Current Limit
The operational amplifiers limit short-circuit current to
approximately ± 150mA if the output is directly shorted
to SUP or to AGND. If the short-circuit condition per-
sists, the junction temperature of the IC rises until it
reaches the thermal-shutdown threshold (+160°C typ).
Once the junction temperature reaches the thermal-
shutdown threshold, an internal thermal sensor immedi-
ately sets the thermal fault latch, shutting off all the IC’s
outputs. The device remains inactive until the input volt-
age is cycled.
Driving Pure Capacitive Loads
The operational amplifiers are typically used to drive
the LCD backplane (VCOM) or the gamma-correction-
divider string. The LCD backplane consists of a distrib-
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