L6738A STMicroelectronics, L6738A Datasheet - Page 19

• Manufacturer Part Number: L6738A
• Description: Current Mode PWM Controllers Single-phase PWM Light Load EFF
• Manufacturer: STMicroelectronics

Specifications of L6738A

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

L6738A
7
Figure 7.
Main oscillator
The controller embeds a programmable oscillator. The internal oscillator generates the
sawtooth waveform for the PWM charging with a constant current and resetting an internal
capacitor. The switching frequency, F
The current delivered to the oscillator is typically 20 µA (corresponding to the free running
frequency F
connected between the OSC pin and GND. As the OSC pin is fixed at 1.240 V, the
frequency is varied proportionally to the current sunk from the pin considering the internal
gain of 10 KHz/µA (see
Connecting R
according to the following relationships:
Connecting R
pin), according to the following relationships:
where +V is the positive voltage to which the R
R
OSC
vs. switching frequency
SW
OSC
OSC
=200 kHz) and it may be varied using an external resistor (R
to GND, the frequency is increased (current is sunk from the pin),
to a positive voltage, the frequency is reduced (current is forced into the
Figure
F
SW
F
Doc ID 18134 Rev 1
7).
SW
=
=
200kHz
200kHz
SW
, is internally fixed at 200 kHz.
–
+
+V 1.240
--------------------------- -
1.240V
------------------ -
OSC
R
R
–
OSC
OSC
resistor is connected.
⋅
⋅
10
10
kHz
---------- -
µA
kHz
---------- -
µA
OSC
Main oscillator
) typically
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