LTC3736EUF-2#PBF Linear Technology, LTC3736EUF-2#PBF Datasheet - Page 21

• Manufacturer Part Number: LTC3736EUF-2#PBF
• Description: IC CTRLR SW SYNC DUAL 2PH 24QFN
• Manufacturer: Linear Technology
• Series: PolyPhase®r
• Type: Step-Down (Buck)r

Specifications of LTC3736EUF-2#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.6 ~ 9.8 V
• Current - Output: 1A
• Frequency - Switching: 550kHz ~ 750kHz
• Voltage - Input: 2.75 ~ 9.8 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
If V
temporary continuous switching operation until V
again above its minimum.
Table 3 summarizes the different states in which the
SYNC/FCB pin can be used.
Table 3
SYNC/FCB PIN
0V to 0.5V
0.7V to V
Feedback Resistors
External Clock Signal
Fault Condition: Short-Circuit and Current Limit
To prevent excessive heating of the bottom MOSFET, fold-
back current limiting can be added to reduce the current
in proportion to the severity of the fault.
Foldback current limiting is implemented by adding
diodes D
pin as shown in Figure 11. In a hard short (V
the current will be reduced to approximately 50% of the
maximum output current.
Low Supply Operation
Although the LTC3736-2 can function down to below
2.4V, the maximum allowable output current is reduced
as V
of change as the supply is reduced down to 2.4V. Also
shown is the effect on V
AUX
IN
decreases below 3V. Figure 12 shows the amount
IN
drops below this value, the FCB voltage forces
Figures 10. Auxiliary Output Loop Connection
FB1
R6
R5
SYNC/FCB
and D
LTC3736-2
SW
FB2
TG
BG
between the output and the I
REF
CONDITION
Forced Continuous Mode
Current Reversal Allowed
Pulse-Skipping Operation Enabled
No Current Reversal Allowed
Regulate an Auxiliary Winding
Enable Phase-Locked Loop
(Synchronize to External CLK)
Pulse-Skipping at Light Loads
No Current Reversal Allowed
V
.
IN
1:N
L1
+
+
37362 F10
1μF
C
OUT
OUT
V
V
AUX
OUT
= 0V),
AUX
TH
is
Minimum On-Time Considerations
Minimum on-time, t
that the LTC3736-2 is capable of turning the top P-chan-
nel MOSFET on and then off. It is determined by internal
timing delays and the gate charge required to turn on the
top MOSFET. Low duty cycle and high frequency applica-
tions may approach the minimum on-time limit and care
should be taken to ensure that:
If the duty cycle falls below what can be accommodated
by the minimum on-time, the LTC3736-2 will begin to
skip cycles (unless forced continuous mode is selected).
The output voltage will continue to be regulated, but the
ripple current and ripple voltage will increase. The mini-
mum on-time for the LTC3736-2 is typically about 200ns.
However, as the peak sense voltage (I
decreases, the minimum on-time gradually increases up
to about 250ns. This is of particular concern in forced
t
ON MIN
(
Figures 12. Line Regulation of V
Maximum Sense Voltage for Low Input Supply
)
Figures 11. Foldback Current Limiting
105
100
<
95
90
85
80
75
2.0
f
OSC
V
2.1
OUT
I
1/2 LTC3736-2
TH
ON(MIN)
V
•
2.2
REF
V
IN
2.3
INPUT VOLTAGE (V)
MAXIMUM
SENSE VOLTAGE
V
2.4
, is the smallest amount of time
FB
2.5
2.6
R2
R1
2.7
LTC3736-2
+
REF
2.8
L(PEAK)
and
2.9
37362 F12
37362 F11
D
D
3.0
FB1
FB2
V
OUT
• R
21
DS(ON)
37362fb
)