LTC3455EUF#TRPBF Linear Technology, LTC3455EUF#TRPBF Datasheet - Page 19

• Manufacturer Part Number: LTC3455EUF#TRPBF
• Description: IC CONV DC/DC DUAL USBBATT 24QFN
• Manufacturer: Linear Technology

Specifications of LTC3455EUF#TRPBF

• Applications: Handheld/Mobile Devices
• Voltage - Supply: 3 V ~ 6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Supply: -

APPLICATIONS INFORMATION
Programming Switching Regulator Output Voltage
The output voltage for each switching regulator is pro-
grammed using a resistor divider from the output connected
to the feedback pins (FB1 and FB2):
Typical values for R1 are in the range of 80k to 400k.
Burst Mode Operation
For highest effi ciencies at light loads, both DC/DC convert-
ers are capable of operating in Burst Mode. In this mode,
energy is delivered to the outputs in shorts bursts, which
minimizes switching losses and quiescent-current losses.
Output voltage ripple is slightly higher in this mode, but
effi ciency is greatly improved. As shown in Figure 8, the
effi ciency at low load currents increases signifi cantly when
Burst Mode operation is used.
V
OUT
=
100
Figure 8. PWM and Burst Mode Effi ciency
0 8
90
80
70
60
50
40
30
20
.
Figure 7. Setting the Output Voltage
1
Burst Mode
3.3V
Burst
Mode
V
1.8V
•
LTC3455-1
LTC3455/
⎛
⎜
⎝
1
PWM Mode
1.8V
FB1, FB2
+
LOAD CURRENT (mA)
R
GND
R
10
2
1
PWM Mode
⎞
⎟
⎠
25
1, 18
3.3V
100
V
BAT
V
OUT
= 3.6V
R2
R1
3455 F08
3455 F07
1000
Tie the MODE pin to V
Mode operation. Even when the MODE pin is high, the
LTC3455/LTC3455-1 will only enter Burst Mode when the
load current is low. For many noise-sensitive systems, Burst
Mode operation might be undesirable at certain times (i.e.
during a transmit or receive cycle of a wireless device),
but highly desirable at others (i.e. when the device is in
low-power standby mode). The MODE pin can be used to
enable or disable Burst Mode operation at any time, offering
both low-noise and low-power operation when they are
needed the most. Burst Mode is disabled initially at startup
(for the fi rst 200ms) and also whenever external power is
available, even if the MODE pin is pulled high.
Figure 9 shows the switching waveforms for switcher 1
(both PWM mode and Burst Mode Operation) with V
3.6V, V
AC-COUPLED
AC-COUPLED
100mA/DIV
100mA/DIV
50mV/DIV
10mV/DIV
OUT1
Figure 9. Burst Mode and PWM Mode Waveforms
2V/DIV
2V/DIV
V
V
V
V
OUT1
OUT1
SW1
SW1
I
I
L1
L1
= 1.8V, and I
LTC3455/LTC3455-1
MAX
OUT1
to always allow automatic Burst
Burst Mode
PWM Mode
5μs/DIV
1μs/DIV
= 25mA.
3455 F09b
3455 F09a
19
3455fc
IN
=