UC3750G-XX-AF5-R UTC [Unisonic Technologies], UC3750G-XX-AF5-R Datasheet - Page 6

• Manufacturer Part Number: UC3750G-XX-AF5-R
• Description: 600kHZ PWM/PFM STEP-DOWN DC-DC CONTROLLER
• Manufacturer: UTC [Unisonic Technologies]

UC3750
1. Detailed Operating Description
battery cells. The UTC UC3750 combines the advantages of Pulse frequency modulation (PFM) and
Constant-frequency pulse width modulation (PWM) which can provide excellent efficiency with light loads and high
efficiency and low output voltage ripple at heavy loads respectively. This device can provide up to 2.0 A loading
current with appropriate external P-type MOSFET connected. Because of working at high switching frequency, it’ s
possible to use small size surface mount inductor and capacitors to reduce PCB area and provide better interference
handling for noise sensitive applications.
2. The Internal Oscillator
an internal Fixed− frequency oscillator. The oscillator signal generates all the using timing signals. And the oscillator
frequency is set to 600 kHz ±15%.
3. Voltage Reference and Soft-Start
voltage during the power-up of the converter. This function effectively enables the output voltage rise gradually over
the specified soft-start time (8 ms typ.), which prevents the output voltage from overshooting during startup of the
converter.
the inverting input terminal of the error amplifier (EA), A1, which compared with portion of the output voltage that is
derived from an integrated voltage divider with precise trimming to give the required output voltage with ±2%
accuracy.
4. Voltage Mode Pulse width modulation (PWM) Control Scheme
controller operates with the internal oscillator which generates the required ramp function to compare with the output
of the error amplifier (EA), A1. The error amplifier (EA) compares the internally divided-down output voltage with the
voltage reference to produce an error voltage at its output. This error voltage is compared with the ramp function to
generate the control pulse to drive the external power switch. On a cycle-by-cycle basis, the greater the error voltage
is greater; the switch is held on longer. Hence, corresponding corrective action will be made to keep the output
voltage within regulation. Constant-frequency PWM reduces output voltage ripple and noise, which is one of the
important characteristics for noise sensitive communication applications. The high switching frequency allows small
size surface mount components to improve layout compactness, reducing PC board area, eliminating audio and
emission interference.
5. Power-Saving Pulse-Frequency-Modulation (PFM) Control Scheme
means the inductor current will decrease to 0 before the next switching cycle starts. In DCM operation, the ON time
for each switching cycle will decrease significantly when the output current decreases. In order to maintain high
conversion efficiency even at light load conditions, the ON time for each switching cycle is closely monitored and for
any ON time is smaller than the preset value (320 ns), the switching pulse will be skipped. As a result, when the
loading current is small, the converter will be operating in a “Constant ON time (320 ns nominal), variable OFF time”
Pulse frequency modulation (PFM) mode. This innovative control scheme improves the conversion efficiency for the
system at light load and standby operating conditions hence extend the operating life of the battery.
6. Low Power Shutdown Mode
oscillator, control circuitry, driver and internal feedback voltage divider are turned off and the output voltage falls to 0
V. Because most of the internal circuits can’t work and the current paths are cut-off, the device consume rather small
in this condition.
7. Under-Voltage Lockout (UVLO)
voltage levels. The comparator will turn-off the control circuitry and shut the converter down, once the input supply
voltage drops below about 2.2 V.
The UTC UC3750 is a step-down DC−DC controllers designed specially in portable applications powered by
The UTC UC3750 needs an oscillator to govern the switching of a PWM control cycles. The UTC UC3750 has
The UTC UC3750 has a built-in soft-start (SS) circuit that controls the ramping up of the internal reference
The UTC UC3750 includes an internal high accuracy voltage reference. This reference voltage is connected to
The UTC UC3750 is working in constant-frequency pulse width modulation (PWM) voltage mode control. The
The converter enters the discontinuous conduction mode (DCM) operation when the load is decreasing, which
Once the CE pin is tied to GND the UTC UC3750 can’t work. In shutdown mode, the internal reference,
The UTC UC3750 incorporated the UVLO to prevent operation of the P-channel MOSFET below rated input
DESCRIPTION INFORMATION
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
Preliminary
QW-R502-360.a
CMOS IC
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