LM2640MTC-ADJ National Semiconductor, LM2640MTC-ADJ Datasheet - Page 11

• Manufacturer Part Number: LM2640MTC-ADJ
• Description: Dual Adjustable Step-Down Switching Power Supply Controller
• Manufacturer: National Semiconductor

Typical Performance Characteristics
REF Output Voltage
Normalized Error Amplifier
Offset vs Junction Temperature
Normalized Oscillator Frequency
vs. Junction Temperature
Theory of Operation
Basic Operation of the Current-Mode Controller
The output voltage is held at a constant value by the main
control loop, which is made up of the error amplifier , the cur-
rent sense amplifier , and the PWM comparator (refer to the
Block Diagram, Figure 3 ).
The LM2640 controller has two primary modes of operation:
Forced Pulse-Width Modulation (FPWM) where the control-
DS100148-32
DS100148-26
DS100148-29
REF Output Voltage
Error Amplifier Gm vs
Junction Temperature
CH1 Skip Frequency
vs Load Current
11
(Continued)
ler always operates at a fixed frequency, and Pulse-Skipping
mode where the controller frequency decreases at reduced
output loads to improve light-load efficiency.
FPWM Mode of Operation
Pulling the FPWM pin low initiates a mode of operation
called Forced Pulse-Width Modulation (FPWM). This means
that the LM2640 will always operate at a fixed frequency, re-
gardless of output load. The cycle of operation is:
The high-side FET switch turns ON at the beginning of every
clock cycle, causing current to flow through the inductor. The
DS100148-30
DS100148-33
DS100148-27
Normalized Switching
Output Voltage vs
Junction Temperature
CH1 Skip Frequency
vs Load Current
Shutdown Quiescent Current
And Standby Quiescent
Current vs Supply Voltage
www.national.com
DS100148-34
DS100148-31
DS100148-28