LTC3407EMSE-4#PBF Linear Technology, LTC3407EMSE-4#PBF Datasheet - Page 10

• Manufacturer Part Number: LTC3407EMSE-4#PBF
• Description: IC REG DC/DC DUAL 1.5MHZ 10-MSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3407EMSE-4#PBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.6 ~ 5 V
• Current - Output: 1A
• Frequency - Switching: 1.5MHz
• Voltage - Input: 2.5 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP Exposed Pad, 10-HMSOP, 10-eMSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
LTC3407-4
Keeping the current small (<5μA) in these resistors maxi-
mizes effi ciency, but making them too small may allow
stray capacitance to cause noise problems and reduce the
phase margin of the error amp loop.
To improve the frequency response, a feed-forward capaci-
tor C
route the V
inductor or the SW line.
Power-On Reset
The POR pin is an open-drain output which pulls low
when either regulator is out of regulation. When both
output voltages are within ±8.5% of regulation, a timer is
started which releases POR after 2
29ms). This delay can be signifi cantly longer in Burst Mode
operation with low load currents, since the clock cycles
only occur during a burst and there could be milliseconds
of time between bursts. This can be bypassed by tying the
POR output to the MODE/SYNC input, to force pulse-skip-
ping mode during a reset. In addition, if the output voltage
faults during Burst Mode sleep, POR could have a slight
delay for an undervoltage output condition and may not
respond to an overvoltage output. This can be avoided by
using pulse-skipping mode instead. When either channel
is shut down, the POR output is pulled low, since one or
both of the channels are not in regulation.
Mode Selection & Frequency Synchronization
The MODE/SYNC pin is a multipurpose pin which provides
mode selection and frequency synchronization. Connect-
ing this pin to V
provides the best low current effi ciency at the cost of a
higher output voltage ripple. Connecting this pin to ground
selects pulse-skipping mode, which provides the lowest
output ripple, at the cost of low current effi ciency.
The LTC3407-4 can also be synchronized to an external
2.25MHz clock signal (such as the SW pin on another
LTC3407-4) by the MODE/SYNC pin. During synchro-
nization, the mode is set to pulse-skipping and the top
switch turn-on is synchronized to the rising edge of the
external clock.
10
V
OUT
F
may also be used. Great care should be taken to
= 0.6V 1+
FB
line away from noise sources, such as the
IN
enables Burst Mode operation, which
R2
R1
16
clock cycles (about
Checking Transient Response
The regulator loop response can be checked by look-
ing at the load transient response. Switching regulators
take several cycles to respond to a step in load current.
When a load step occurs, V
amount equal to ΔI
series resistance of C
or discharge C
used by the regulator to return V
value. During this recovery time, V
for overshoot or ringing that would indicate a stability
problem.
The initial output voltage step may not be within the
bandwidth of the feedback loop, so the standard second-
order overshoot/DC ratio cannot be used to determine
phase margin. In addition, a feed-forward capacitor, C
can be added to improve the high frequency response, as
shown in Figure 2. Capacitor C
creating a high frequency zero with R2, which improves
the phase margin.
The output voltage settling behavior is related to the stability
of the closed-loop system and will demonstrate the actual
overall supply performance. For a detailed explanation of
optimizing the compensation components, including a re-
view of control loop theory, refer to Application Note 76.
In some applications, a more severe transient can be caused
by switching in loads with large (>1μF) input capacitors.
The discharged input capacitors are effectively put in paral-
lel with C
can deliver enough current to prevent this problem, if the
switch connecting the load has low resistance and is driven
quickly. The solution is to limit the turn-on speed of the
load switch driver. A Hot Swap™ controller is designed
specifi cally for this purpose and usually incorporates cur-
rent limiting, short-circuit protection, and soft-starting.
Effi ciency Considerations
The percent effi ciency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
what is limiting the effi ciency and which change would
Hot Swap is a trademark of Linear Technology Corporation.
OUT
, causing a rapid drop in V
OUT
, generating a feedback error signal
LOAD
OUT
• ESR, where ESR is the effective
. ΔI
OUT
LOAD
F
immediately shifts by an
provides phase lead by
OUT
also begins to charge
OUT
to its steady-state
can be monitored
OUT
. No regulator
34074fa
F
,