LM3488MM/NOPB National Semiconductor, LM3488MM/NOPB Datasheet - Page 10

• Manufacturer Part Number: LM3488MM/NOPB
• Description: IC CTRLR SWITCH REG N-CH 8-MSOP
• Manufacturer: National Semiconductor
• Type: Step-Up (Boost), Flyback, Sepicr

Specifications of LM3488MM/NOPB

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: Adj to 1.26V
• Current - Output: 1A
• Frequency - Switching: 100kHz ~ 1MHz
• Voltage - Input: 2.97 ~ 40 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: LM3488MM; LM3488MM; LM3488MMTR

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SLOPE COMPENSATION RAMP
The LM3488 uses a current mode control scheme. The main
advantages of current mode control are inherent cycle-by-cy-
cle current limit for the switch, and simpler control loop char-
acteristics. It is also easy to parallel power stages using
current mode control since as current sharing is automatic.
Current mode control has an inherent instability for duty cy-
cles greater than 50%, as shown in
small increase in the load current causes the switch current
to increase by ΔI
O
. The effect of this load change, ΔI
FIGURE 1. Basic Operation of the PWM comparator
Figure
FIGURE 2. Sub-Harmonic Oscillation for D>0.5
2. In
Figure
1
, is :
2, a
10
From the above equation, when D > 0.5, ΔI
than ΔI
very small perturbation in the load will cause the disturbance
to increase.
To prevent the sub-harmonic oscillations, a compensation
ramp is added to the control signal, as shown in
With the compensation ramp,
O
. In other words, the disturbance is divergent. So a
1
10138809
will be greater
Figure
10138807
3.