A6902D データシートの表示（PDF） - STMicroelectronics
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A6902D Datasheet PDF : 33 Pages
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A6902D
Functional description
5
Functional description
The main internal blocks are shown in the device block diagram in figure below.
• A voltage regulator supplying the internal circuitry.
• A voltage monitor circuit checks the input and the internal voltages.
• A fully integrated sawtooth oscillator with a frequency of 250 kHz ± 15 %, including also the voltage feed
forward function.
• Two embedded current limitation circuits which control the current that flows through the power switch. The
pulse-by-pulse current limit forces the power switch OFF cycle by cycle if the current reaches an internal
threshold, while the frequency shifter reduces the switching frequency in order to significantly reduce the
duty cycle.
• A transconductance error amplifier for output voltage regulation.
• A transconductance error amplifier for adjustable constant current operation.
• A pulse width modulator (PWM) comparator and the relative logic circuitry necessary to drive the internal
power.
• A high side driver for the internal P-MOS switch.
• An inhibit block for stand-by operation.
• A circuit to implement the thermal protection function.
Figure 2. Block diagram
VCC
CS+
CS-
Current E/A
+
-
VOLTAGES
MONITOR
SUPPLY
THERMAL
SHUTDOWN
1.235V
3.5V
VREF
BUFFER
VREF
COMP
FB
Voltage E/A
-
+
1.235V
+
PWM
-
OSCILLATOR
PEAK TO PEAK
CURRENT LIMIT
DQ
DRIVER
Q
FREQUENCY
SHIFTER
PDMOS
POWER
GND
OUT
5.1
Power supply and voltage reference
The internal regulator circuit (shown in Figure 3. Internal circuit) consists of a start-up circuit, an internal voltage
pre-regulator, the Bandgap voltage reference and the Bias block that provides current to all the blocks. The pre-
regulator block supplies the Bandgap cell with a pre-regulated voltage VREG that has a very low supply voltage
noise sensitivity.
DS5503 - Rev 6
page 6/33
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