AA18375AP Agamem Microelectronic, AA18375AP Datasheet - Page 8

• Manufacturer Part Number: AA18375AP
• Description: Switching Regulator Controller
• Manufacturer: Agamem Microelectronic

PRELIMINARY
■ OPERATION DESCRIPTION
1. Reference voltage
2. Oscillator
3. Error amplifiers
4. Timer latch short protection circuit
5. Under voltage lockout protection circuit
6. PWM comparator
7. Output drive transistor
©Copyright Agamem Microelectronics Inc.
This block is composed of the band gap circuit, and outputs the temperature compensated 2.5 V reference from
Vcc (pin 9) for use by internal circuits. A reference voltage of temperature compensated 1/2 Vref can be
obtained to external circuit by Vref terminal (pin 16).
The sawtooth-waveform-like triangular wave having a peak of approximately 1.9 V and a trough of
approximately 1.3 V can be generated by connecting the timing capacitor C
The usable oscillation frequency is from 1 kHz to the maximum 500 KHz. The triangular wave is
connected with the non-inverting input of PWM comparator for channel 1 side and channel 2 side within
the IC inside.
The output voltage of DC-DC converter is detected by the error-amplifier and the amplified signal is input
to the PWM comparator. Also, it is possible to perform the gain setting and the phase compensation
arbitrarily by connecting a resistor and a capacitor from the FB terminals (pins 5 and 12) to GND. The
error amplifier output is internally connected to the inverting inputs of the PWM comparators and also to
the short protection circuit.
This circuit protects the external main switching devices, flywheel diodes, and choke coils, etc. from
destruction or deterioration if overload or short-circuit condition of power supply output lasts for a certain
time. The timer latch short-circuit protection circuit detects the output level of the error amplifier. If one or
both error amplifier outputs are 1.1 V or lower, the low-level output is given and the timer circuit is
actuated to start the charge of the external protection-enable capacitor.
If the output level of the error amplifier does not drop below the normal voltage range before the capacitor
voltage reaches the 1.19 V, it sets the latch circuit, and cuts off the output drive transistor, and sets the
dead-time to 100%.
This circuit protects the system from destruction or deterioration due to control malfunction when the
supply voltage is low in the transient state of power on/off. The under voltage lockout protection circuit
compares the internal reference voltage level with the supply voltage level. If the supply voltage level falls
below the reference level it cuts off the output drive transistor, and sets the dead time to 100%. The
protection enable terminal (pin 15) is pulled “Low”.
Each PWM comparator has two inverting inputs and one non-inverting input. This voltage-to-pulse-width
converter controls the output pulse width according to the input voltage. The PWM comparator turns the
output drive transistor on when the oscillator triangular waveform is higher than the error amplifier output
and the dead time control terminal voltage.
This output circuit is open-collector type. The available output current is up to 50 mA. The breakdown
voltage of output terminal is 15V.
Agamem Microelectronics Inc.
8
AA18375AP
Switching Regulator Controller
www.agamem.com.tw
T
(pin 1) and resistor R
2006/6/27
T
(pin 2).