Sharp LC-32LE140E, Service Manual

Page: 47 / 88

47
LC-32LE140
Pin No. Pin
Name
Description
1 BOOT
Bootstrap for high-side gate driver. Connect a 0.1
μ
F or
greater ceramic capacitor from BOOT to SW pins.
2 VIN Input Supply 4.5V to 23V. Must bypass with a suitably
large ceramic capacitor.
3
SW Phase Node--Connect to external L-C filter..
4, 9 (Exposed
Pad)
GND Ground.
5 FB Feedback Input pin is connected to the converter output.
It is used to set the output of the converter to regulate to
the desired value via an internal res divider. For an
adjustable output, an external res divider is connected to
this pin.
6 COMP Compensation Node. COMP is used to compensate the
regulation Control loop. Connect a series RC network
from COMP to GND. In some cases, an additional
capacitor from COMP to GND is required.
7 EN Enable Input Pin. Logic high enables the converter; a
logic low forces the RT8253A into shutdown mode.
Attach this pin to VIN with a 100kΩ pull up resistor for
automatic startup.
8 SS Soft-Start Control Input. SS controls the soft-start period.
Connect a capacitor from SS to GND to set the soft-start
period. A 0.1
μ F capacitor sets the soft-start period to
13.5ms.
1
5
. MP1583 (U174)
1
5
.1. General Description
The MP1583 is a step-down regulator with a built-in internal Power MOSFET. It achieves
3A of continuous output current over a wide input supply range with excellent load and
line regulation. Current mode operation provides fast transient response and eases loop
stabilization. Fault condition protection includes cycle-by-cycle current limiting and thermal
shutdown. An adjustable soft-start reduces the stress on the input source at start-up. The
MP1583 requires a minimum number of external components, providing a compact
solution.
1
5
.2. Features
 3A Output Current
 Programmable Soft-Start
 100mΩ Internal Power MOSFET Switch
 Stable with Low ESR Output Ceramic Capacitors
 Up to 95% Efficiency
 20μA Shutdown Mode
 Fixed 385KHz Frequency
 Thermal Shutdown
 Cycle-by-Cycle Over Current Protection
 Wide 4.75V to 23V Operating Input Range
 Output Adjustable from 1.22V to 21V
 Under-Voltage Lockout
15.3. Pinning
Pin
No.
Pin
Name
Description
1 BOOT High-Side Gate Drive Bootstrap Input. BS supplies the drive for the
high-side N-Channel MOSFET switch.
2
IN Power Input. Drive IN with a 4.75V to 23V power source.
3
SW Power Switching Out is the switching node that supplies power to the
output
4 GND Ground.
5 FB Feedback Input. FB senses the output voltage and regulates it. Drive
FB with a resistive voltage divider from the output voltage. FB
threshold is 1.222V.
6
COMP Compensation Node is used to compensate the regulation control
loop.
7 EN Enable/UVLO. A voltage greater than 2.71V enables operation. For
complete low current shutdown the EN pin voltage needs to be at less
than 900mV. When the voltage on EN exceeds 1.2V, the internal
regulator will be enabled and the soft-start capacitor will begin to
charge. The MP1583 will start switching after the EN pin voltage
reaches 2.71V.
8
SS Soft-Start Control Input. SS controls the soft-start period.
16. FDC642
16.1. General Description
This P-Channel 2.5V specified MOSFET is produced using Fairchild’s advanced
PowerTrench ® process that has been especially tailored to minimize on-state resistance
and yet maintain low gate charge for superior switching performance.
These devices have been designed to offer exceptional power dissipation in a very small
footprint for applications where the larger packages are impractical.
16.2. Features
 Max rDS(on) = 65 mΩ at VGS = -4.5 V, ID = -4.0 A
 Max rDS(on) = 100 mΩ at VGS = -2.5 V, ID = -3.2 A
 Fast switching speed
 Low gate charge (11nC typical)