AA1700 Agamem Microelectronic, AA1700 Datasheet - Page 6

• Manufacturer Part Number: AA1700
• Description: Constant Current White LED Driver
• Manufacturer: Agamem Microelectronic

PRELIMINARY
■FUNCTIONAL DESCRIPTION
1. Switching Regulator Function
(1) Sawtooth wave oscillator
This circuit generates a triangular wave like sawtooth with a peak of 0.8V (
using a capacitor (for the time constant) and resistor connected to the CLK pin (pin 7). The oscillator frequency
can be set to any value by selecting appropriate values for the external capacitor and resistor, C
oscillator can provide a frequency in the range 10 kHz to 1 MHz.
(2) Error amplifier
This error amplifier detects and amplifies the DC-DC converter output voltage, and inputs that signal to a PWM
comparator. The 0.5 V internal reference voltage is applied to the non-inverting input. Arbitrary gain and phase
compensation can be connected by inserting a resistor and capacitor in series between the error amplifier output
pin (pin 8) and the inverting input pin (pin 1).
(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-period of the output pulse according to its input voltage. The output
transistors are turned on during periods when the CLK pin (pin 7) triangular waveform is lower than the error
amplifier output voltage, soft start setting voltage, and idle period setting voltage.
(4) Output driver
The output circuit has a totem pole structure. A constant-current source output with line regulation can be set up
at an arbitrary voltage by connecting a current setting resistor to the CTL pin (pin 4).
2. Power Supply On/Off Function
Stand-by mode (supply current 1 µA or less) can be set by connecting the CTL pin (pin 4) to V
the pin open circuit.
©Copyright Agamem Microelectronics Inc.
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Constant Current White LED driver
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