LT3581IMSE-TRPBF 데이터 시트보기 (PDF) - Linear Technology
부품명
상세내역
제조사
LT3581IMSE-TRPBF Datasheet PDF : 36 Pages
| |||
LT3581
APPENDIX
found. Figures 15a to 15c illustrate this process for the
circuit of Figure 18 with a load current stepped between
540mA and 800mA. Figure 15a shows the transient re-
sponse with RC equal to 1k. The phase margin is poor as
evidenced by the excessive ringing in the output voltage
and inductor current. In Figure 15b, the value of RC is
increased to 3k, which results in a more damped response.
Figure 15c shows the results when RC is increased further
to 10.5k. The transient response is nicely damped and the
compensation procedure is complete.
VOUT
AC-COUPLED
500mV/DIV
IL
1A/DIV
50µs/DIV
3581 F15a
Figure 15a. Transient Response Shows Excessive Ringing
VOUT
AC-COUPLED
500mV/DIV
COMPENSATION – THEORY
Like all other current mode switching regulators, the LT3581
needs to be compensated for stable and efficient operation.
Two feedback loops are used in the LT3581: a fast current
loop which does not require compensation, and a slower
voltage loop which does. Standard Bode plot analysis can be
used to understand and adjust the voltage feedback loop.
As with any feedback loop, identifying the gain and
phase contribution of the various elements in the loop
is critical. Figure 16 shows the key equivalent elements
of a boost converter. Because of the fast current control
loop, the power stage of the IC, inductor and diode
have been replaced by a combination of the equivalent
transconductance amplifier gmp and the current controlled
current source (which converts IVIN to ηVIN/VOUT • IVIN).
gmp acts as a current source where the peak input current,
IVIN, is proportional to the VC voltage. η is the efficiency
of the switching regulator and is typically about 80%.
Note that the maximum output currents of the gmp and
gma stages are finite. The output of the gmp stage is
limited by the minimum switch current limit (see Electrical
Specifications) and the output of the gma stage is nominally
limited to about ±12μA.
IL
1A/DIV
50µs/DIV
3581 F15b
Figure 15b. Transient Response is Better
VOUT
AC-COUPLED
500mV/DIV
–
gmp
+
IVIN
η • VIN
VOUT
•
IVIN
1.215V
REFERENCE
VOUT
RESR RL
COUT
CPL R1
VC
gma
CF RC RO
CC
R2
FB
R2
3581 F16
IL
1A/DIV
50µs/DIV
3581 F15c
Figure 15c. Transient Response is Well Damped
CC: COMPENSATION CAPACITOR
COUT: OUTPUT CAPACITOR
CPL: PHASE LEAD CAPACITOR
CF: HIGH FREQUENCY FILTER CAPACITOR
gma: TRANSCONDUCTOR AMPLIFIER INSIDE IC
gmp: POWER STAGE TRANSCONDUCTANCE AMPLIFIER
RC: COMPENSATION RESISTOR
RL: OUTPUT RESISTANCE DEFINED AS VOUT/ILOAD(MAX)
RO: OUTPUT RESISTANCE OF gma
R1, R2; FEEDBACK RESISTOR DIVIDER NETWORK
RESR: OUTPUT CAPACITOR ESR
Figure 16. Boost Converter Equivalent Model
26
For more information www.linear.com/LT3581
3581fb
Share Link: 