CP3800
Switching Regulator Power Controller
Switching Regulator Function
(1) Reference voltage circuit
The reference voltage circuit generates a temperature-compensated reference voltage (~1.25V)
from voltage supplied from the power supply pin (pin 3). In addition to providing the reference
voltage for the switching regulator, the circuit also sets the idle period.
(2) Error amplifier
The error amplifier detects the output voltage of the switching regulator and outputs the PWM
control signal. The voltage gain is fixed, and connecting a phase compensation capacitor to the
FB pin (pin 8) provides stable phase compensation for the system.
(3) PWM comparator
The voltage comparator has one inverting and three non-inverting inputs. The comparator is a
voltage/pulse width converter that controls the ON time of the output pulse depending on the
input voltage. The output level is high (H) when the sawtooth wave is lower than the error
amplifier output voltage, soft start setting voltage, and idle period setting voltage.
(4) Output circuit
The output circuit has a totem pole type configuration and can drive an external NPN transistor
directly. The value of the ON/OFF current can be set by a resistor connected to the BR/CTL pin
(pin 4). Stand-by mode (supply current 1µA or less) can be set by connecting the BR/CTL pin
(pin4) to VCC or by making the pin open circuit.
(5) Under-Voltage Lockout (UVLO)
Transients when powering on or instantaneous glitches in the supply voltage can lead to
malfunction of the control IC and cause system damage or failure. The circuit to prevent
malfunction at low input voltage detects a low input voltage by comparing the supply voltage to
the internal reference voltage. On detection, the circuit fixes the output pin to low.
To cancel the status, set VCC below the reset voltage VR (0.9V) and then set VCC up to the
recommended operation condition range. By the operation, the latch is canceled to start to operate
normally.
* All specs and applications shown above subject to change without prior notice.
1F-5 NO.66 SEC.2 NAN-KAN RD ., LUCHU , TAOYUAN, TAIWAN
Tel:886-3-3214525
Email: server@ceramate.com.tw
Http: www.ceramate.com.tw
Rev 1.0 Mar.31,2003
Page 16 of 19
Fax:886-3-3521052
CERAMATE [ CERAMATE TECHNICAL ]
