mc33680ftb ON Semiconductor, mc33680ftb Datasheet - Page 10

• Manufacturer Part Number: mc33680ftb
• Description: Dual Dc-dc Regulator For Electronic Organizer
• Manufacturer: ON Semiconductor

Iref
Conduction Mode, waveforms are similar to those of Figure
19. However, coil current drops to zero before next
switching cycle starts.
used.
mode
where coil current just drops to zero and next cycle starts.
mode
limit is not reached,
DETAILED OPERATING DESCRIPTION (Cont’d)
where, η is efficiency, refer to Figure 4
In Figure 20, regulator is operating at Discontinuous
To estimate conduction mode, below equation can be
if I
if I
if I
For Continuous Conduction mode, provided that current
RIref
480 kOhm
Iroom +
room
room
room
IREF
8
> 0, the regulator is at Discontinuous Conduction
= 0, the regulator is at Critical Conduction mode
< 0, the regulator is at Continuous Conduction
h
Voltage Reference
& Current Bias
2
Reference
x2
Voltage
T
ON
L
Vout
Vin 2
AGND
1.22 V
0.5 V
* I
LOAD
Figure 18. Simplified Block Diagram of Main Regulator
COMP1
2 x Iref
Main Regulator
with Synchronous Rectifier
1
VMAINFB
VCOMP
http://onsemi.com
for Max. ON Time
+ve Edge Delay
for Min. OFF Time
1−SHOT
10
R
S
current limit is not reached,
Qb
For Discontinuous Conduction mode, provided that
T
Q
T
I
SW
1000 kOhm
SW
pk
CMAINb
RMAINb
I
100 pF
pk
+
ZLC
+
+
+ Vin
1 *
DGND
2 @ L @ I
1 * h
V
R
S
L
DD
I
LOAD
COMP3
@ T
T
Q
T
T
ON
SW
ON
ON
Vout
LOAD
Vin
Vin @ T
(A)
31
)
ILIM
VBAT
@
(S);
Vin
ON
M1
2
VMAINSW
h@Vin
2
Vout
L1
33uH
AGND
COMP2
T
DGND
L
ON
senseFET
V
* 1
DD
(A)
M2
(S);
VMAIN
CMAIN
32
100 uF
30
VMAINGND
+