Kingbor Technology Co.,Ltd
TEL:(86)0755-26508846 FAX:(86)0755-26509052
kB3440
OPERATION
voltagefromtheerroramptodeterminethecontrolmode,
therefore full-time 4-switch mode is required to maintain
the Buck/Boost function. The efficiency below 1mA
becomes dominated primarily by the quiescent current
and not the peak efficiency. The equation is given by:
Burst Mode Operation to Fixed Frequency Transient
Response
When transitioning from Burst Mode operation to fixed
frequency,thesystemexhibitsatransientsincethemodes
of operation have changed. For most systems this tran-
sient is acceptable, but the application may have stringent
input current and/or output voltage requirements that
dictate a broad-band voltage loop to minimize the tran-
sient. Lowering the DC gain of the loop will facilitate the
task (10M FB to VC) at the expense of DC load regulation.
Type 3 compensation is also recommended to broad band
the loop and roll off past the two pole response of the LC
of the converter (see Closing the Feedback Loop).
(dbm)•ILOAD
Efficiency Burst 5
25µA +ILOAD
where (dbm) is typically 79% during Burst Mode opera-
tion for an ESR of the inductor of 50m1. For 200m1 of
inductor ESR, the peak efficiency (dbm) drops to 75%.
V
V
D
IN
OUT
6
7
V
L
dI
dT
IN
A
5
+
–
400mA
3
4
L
SW1
SW2
B
C
0mA
3440 F03
T1
5
GND
Figure 3. Inductor Charge Cycle During Burst Mode Operation
V
V
D
IN
OUT
6
7
V
dI
dT
OUT
L
+
A
5 –
–
400mA
0mA
3
4
L
SW1
SW2
B
C
3440 F04
T2
5
GND
Figure 4. Inductor Discharge Cycle During Burst Mode Operation
10
KINGBOR [ KINGBOR TECHNOLOGY CO ]
