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LTC3405AES6-1.8#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
4
LTC3405A-1.5/LTC3405A-1.8
3405a1518fa
Dynamic Supply Current
vs Supply Voltage
Dynamic Supply Current
vs Temperature
Switch Leakage vs Temperature
Switch Leakage vs Input Voltage
SUPPLY VOLTAGE (V)
2
0
SUPPLY CURRENT (µA)
200
600
800
1000
4
1800
3405A1518 G12
400
3
2.5
4.5 5
3.5 5.5
1200
1400
1600
PULSE SKIPPING MODE
BURST MODE OPERATION
V
OUT
= 1.8V
I
LOAD
= 0A
TEMPERATURE (°C)
–50
SWITCH LEAKAGE (nA)
160
140
120
100
80
60
40
20
0
25 75
–25 0
50 100 125
V
IN
= 5.5V
RUN = 0V
3405F G14
MAIN SWITCH
SYNCHRONOUS
SWITCH
INPUT VOLTAGE (V)
0
SWITCH LEAKAGE (pA)
60
50
40
30
20
10
0
1
234
3405F G15
56
RUN = 0V
MAIN SWITCH
SYNCHRONOUS
SWITCH
SW
5V/DIV
V
OUT
100mV/DIV
AC COUPLED
I
L
100mA/DIV
3405A1518 G16
5µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
=
20mA
SW
5V/DIV
V
OUT
10mV/DIV
AC
COUPLED
I
L
100mA/DIV
3405A1518 G17
500ns/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
=
20mA
RUN
2V/DIV
V
OUT
1V/DIV
I
L
200mA/DIV
3405A1518 G18
100µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
=
250mA
3405A1518 G19
V
OUT
100mV/DIV
AC
COUPLED
I
LOAD
200mA/DIV
I
L
200mA/DIV
40µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 0mA TO 250mA
PULSE SKIPPING MODE
TYPICAL PERFOR A CE CHARACTERISTICS
UW
(From Figure 1a)
Burst Mode Operation
Pulse Skipping Mode Operation
Start-Up from Shutdown
Load Step
TEMPERATURE (°C)
–50
300
340
25 75
3405A1518 G13
260
–25 0
50 100 125
220
180
140
100
60
20
0
SUPPLY CURRENT (µA)
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 0A
PULSE SKIPPING MODE
BURST MODE OPERATION
5
LTC3405A-1.5/LTC3405A-1.8
3405a1518fa
UU
U
PI FU CTIO S
RUN (Pin 1): Run Control Input. Forcing this pin above
1.5V enables the part. Forcing this pin below 0.3V shuts
down the device. In shutdown, all functions are disabled
drawing <1µA supply current. Do not leave RUN floating.
GND (Pin 2): Ground Pin.
SW (Pin 3): Switch Node Connection to Inductor. This pin
connects to the drains of the internal main and synchro-
nous power MOSFET switches.
V
IN
(Pin 4): Main Supply Pin. Must be closely decoupled
to GND, Pin 2, with a 2.2µF or greater ceramic capacitor.
V
OUT
(Pin 5): Output Voltage Feedback Pin. An internal
resistive divider divides the output voltage down for com-
parison to the internal 1.2V reference voltage.
MODE (Pin 6): Mode Select Input. To select pulse skip-
ping mode, tie to V
IN
. Grounding this pin selects Burst
Mode operation. Do not leave this pin floating.
3405A1518 G20
V
OUT
100mV/DIV
AC
COUPLED
I
LOAD
200mA/DIV
I
L
200mA/DIV
40µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 20mA TO 250mA
PULSE SKIPPING MODE
V
OUT
100mV/DIV
AC
COUPLED
I
LOAD
200mA/DIV
I
L
200mA/DIV
3405A1518 G21
40µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 20mA TO 250mA
Burst Mode OPERATION
3405A1518 G22
40µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 0mA TO 250mA
Burst Mode OPERATION
V
OUT
100mV/DIV
AC
COUPLED
I
LOAD
200mA/DIV
I
L
200mA/DIV
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Load Step Load Step Load Step
(From Figure 1a)
6
LTC3405A-1.5/LTC3405A-1.8
3405a1518fa
FU CTIO AL DIAGRA
U
U
W
OPERATIO
U
(Refer to Functional Diagram)
Main Control Loop
The LTC3405A Fixed output voltage series parts use a
constant frequency, current mode step-down architec-
ture. Their main (P-channel MOSFET) and synchronous
(N-channel MOSFET) switches are internal. During normal
operation, the internal top power MOSFET is turned on
each cycle when the oscillator sets the RS latch, and turned
off when the current comparator, I
COMP
, resets the RS
latch. The peak inductor current at which I
COMP
resets the
RS latch, is controlled by the output of error amplifier EA.
When the load current increases, the output voltage de-
creases which causes a slight decrease in V
FB
relative to
the 1.2V reference, which in turn, causes the EA amplifier’s
output voltage to increase until the average inductor
current matches the new load current. While the top
MOSFET is off, the bottom MOSFET is turned on until
either the inductor current starts to reverse, as indicated by
the current reversal comparator I
RCMP
, or the beginning of
the next clock cycle.
Comparator OVDET guards against transient overshoots
>7.8% by turning the main switch off and keeping it off
until the fault is removed.
Burst Mode Operation
The LTC3405A series parts are capable of Burst Mode
operation in which the internal power MOSFETs operate
intermittently based on load demand. To enable Burst
Mode operation, simply connect the MODE pin to GND. To
disable Burst Mode operation and enable PWM pulse
skipping mode, connect the MODE pin to V
IN
or drive it
with a logic high (V
MODE
> 1.5V). In this mode, the
efficiency is lower at light loads, but becomes comparable
to Burst Mode operation when the output load exceeds
25mA. The advantage of pulse skipping mode is lower
output ripple and less interference to audio circuitry.
+
–
+
–
+
–
+
–
OVDET
EA
+
–
I
RCMP
+
–
I
COMP
5
1
RUN
OSC
SLOPE
COMP
OSC
FREQ
SHIFT
1.2V
R1
LTC3405A-1.5
R1 = 110k
R2 = 440k
LTC3405A-1.8
R1 = 180k
R2 = 360k
R2
1.294V
1.2V REF
SHUTDOWN
OV
0.4V
0.65V
SLEEP
V
IN
V
OUT
6
MODE
EN
BURST
V
IN
S
R
RS LATCH
SWITCHING
LOGIC
AND
BLANKING
CIRCUIT
ANTI-
SHOOT-
THRU
Q
Q
5Ω
4
SW
3
GND
3405A1518 BD
2
V
FB
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16

LTC3405AES6-1.8#TRPBF

Mfr. #:
Buy LTC3405AES6-1.8#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators 300mA, 1.5MHz Sync Step-dwn cnvtr
Lifecycle:
New from this manufacturer.
Delivery:
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