PM6680 STMicroelectronics, PM6680 Datasheet - Page 23

• Manufacturer Part Number: PM6680
• Description: IC CTRLR DUAL STEP DOWN 32VFQFPN
• Manufacturer: STMicroelectronics

Specifications of PM6680

• Applications: Controller, Notebook Power System
• Voltage - Input: 6 ~ 28 V
• Number Of Outputs: 2
• Voltage - Output: 0.9 ~ 5.5 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-VFQFN, 32-VFQFPN
• Output Voltage: 5 V, 0.9 V to 5.5 V, 0.9 V to 3.3 V
• Output Current: 0.33 A
• Input Voltage: 5.5 V to 28 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 10 C
• For Use With: 497-6379 - BOARD EVALUATION FOR PM6680A497-6378 - BOARD EVALUATION FOR PM6680497-6425 - BOARD EVAL BASED ON PM6680A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

PM6680
7.2
Constant on time architecture
Figure 29
off-time constrain (300 ns typ.) is introduced to allow inductor valley current sensing on
synchronous switch. A minimum on-time (70 ns) is also introduced to assure the start-up
switching sequence.
PM6680 has a one-shot generator for each power section that turns on the high side
MOSFET when the following conditions are satisfied simultaneously: the PWM comparator
is high, the synchronous rectifier current is below the current limit threshold, and the
minimum off-time has timed out.
Once the on-time has timed out, the high side switch is turned off, while the synchronous
switch is turned on according to the anti-cross conduction circuitry management.
When the negative input voltage at the PWM comparator
down replica of the output voltage (see the external R1/R2 divider in
valley limit (determined by internal reference Vr = 0.9 V), the low-side MOSFET is turned off
according to the anti-cross conduction logic once again, and a new cycle begins.
Figure 29. Constant on-time block diagram
CSENSE
CSENSE
CSENSE
CSENSE
COMP
COMP
COMP
COMP
SKIP
SKIP
SKIP
SKIP
OUT
OUT
OUT
OUT
VIN
VIN
VIN
VIN
FB
FB
FB
FB
shows the simplified block diagram of a Constant On Time controller. A minimum
Positive
Positive
Positive
Positive
Current
Current
Current
Current
Limit
Limit
Limit
Limit
Vr
Vr
Vr
Vr
gm
gm
gm
gm
Vr
Vr
Vr
Vr
+
+
+
+
+
-
-
-
+
+
Comparato
Comparato
Comparato
Comparato
-
-
PWM
PWM
PWM
PWM
r
r
r
r
0.5V
0.5V
+
+
Toff
Toff
+
+
Toff
Toff
Zero-
Zero-
Zero
Zero
-
-
-
-
Comp.
Comp.
Comp.
Comp.
Ton
Ton
Ton
Ton
-
-
-
-
-
-
min
min
min
min
cross.
cross.
cross.
cross.
S
S
R
R
Q
Q
Q
Q
S
S
R
R
Q
Q
(Figure
LDO5
LDO5
+
+
+
LDO5
LDO5
-
-
-
0.5V
0.5V
0.5V
29), which is a scaled-
Level
Level
Level
Level
shifte
shifte
shifte
shifte
r
r
r
r
Figure
bandga
bandga
bandga
bandga
1.236V
1.236V
1.236V
1.236V
p
p
p
p
Vr
Vr
Vr
Vr
Device description
+
+
+
-
-
-
29), reaches the
HS
HS
HS
HS
driver
driver
driver
driver
LS
LS
driver
driver
LS
LS
driver
driver
LDO5
LDO5
LDO5
LDO5
0.25V
0.25V
0.25V
HGATE
HGATE
HGATE
HGATE
PHASE
PHASE
LGATE
LGATE
LGATE
LGATE
PGND
PGND
PGND
PGND
VREF
VREF
VREF
VREF
BOOT
BOOT
PHASE
PHASE
BOOT
BOOT
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