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PDF LTC3388-3 Data sheet ( Hoja de datos )
| Número de pieza | LTC3388-3 | |
| Descripción | 20V High Efficiency Nanopower Step-Down Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC3388-3 (archivo pdf) en la parte inferior de esta página. Total 22 Páginas | ||
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FEATURES
nn 720nA Input IQ in Regulation (No Load), VIN = 4V
nn 820nA Input IQ in Regulation (No Load), VIN = 20V
nn 400nA Input IQ in UVLO
nn 2.7V to 20V Input Operating Range
nn Up to 50mA of Output Current
nn Pin Selectable Output Voltages:
nn 1.2V, 1.5V, 1.8V, 2.5V (LTC3388-1)
nn 2.8V, 3.0V, 3.3V, 5.0V (LTC3388-3)
nn High Efficiency Hysteretic Synchronous
DC/DC Conversion
nn Standby Mode Disables Buck Switching
nn Available in 10-Lead MSE and 3mm × 3mm
DFN Packages
APPLICATIONS
nn Keep Alive Power for Portable Products
nn Industrial Control Supplies
nn Distributed Power Systems
nn Battery-Operated Devices
LTC3388-1/LTC3388-3
20V High Efficiency
Nanopower
Step-Down Regulator
DESCRIPTION
The LTC®3388-1/LTC3388-3 are high efficiency step-down
DC/DC converters with internal high side and synchronous
power switches that draw only 720nA typical DC supply cur-
rent at no load while maintaining output voltage regulation.
Capable of supplying 50mA of load current, the LTC3388-1/
LTC3388-3 also incorporate an accurate undervoltage
lockout (UVLO) feature to disable the converter and main-
tain a low quiescent current state when the input voltage
falls below 2.3V. In regulation, the LTC3388-1/LTC3388-3
enter a sleep state in which both input and output quies-
cent currents are minimal. The buck converter turns on
and off as needed to maintain regulation. An additional
standby mode disables buck switching while the output is
in regulation for short duration loads requiring low ripple.
Output voltages of 1.2V, 1.5V, 1.8V, 2.5V (LTC3388-1)
and 2.8V, 3.0V, 3.3V, 5.0V (LTC3388-3) are pin selectable.
The LTC3388-1/LTC3388-3 can operate with VIN up to 20V
while the no load quiescent current remains below 1µA.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
TYPICAL APPLICATION
50mA Step-Down Converter
2.7V TO 20V
2.2µF
25V
1µF
6V
4.7µF
6V
VIN
LTC3388-1/
LTC3388-3
CAP
SW
VIN2
VOUT
EN PGOOD
STBY
D0, D1
GND
338813 TA01a
100µH
2 OUTPUT
VOLTAGE
SELECT
VOUT
47µF
6V
Efficiency vs Load Current
100 VOUT = 1.8V, L = 100µH
90
80
70
60
50
40
30
20
10
0
1µ
VIN = 3.0V
VIN = 10V
VIN = 20V
10µ 100µ 1m
LOAD CURRENT (A)
10m
338813 TA01b
For more information www.linear.com/LTC3388
338813fa
1
1 page  
LTC3388-1/LTC3388-3
TYPICAL PERFORMANCE CHARACTERISTICS
UVLO vs Temperature
2.8
2.6
UVLO RISING
2.4 UVLO FALLING
2.2
2.0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
338813 G04
IPEAK vs Temperature
180
170
160
150
140
130
120
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
338813 G05
vRsP,TBeUmCKp/eRrNa,tBuUrCeK
2.0
1.8
NMOS
1.6
1.4
PMOS
1.2
1.0
0.8
–55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C)
338813 G06
Operating Waveforms
VOUT
50mV/DIV
AC-COUPLED
VSW
2V/DIV
0V
INDUCTOR
CURRENT
100mA/DIV
0mA
5µs/DIV
VIN = 5.5V, VOUT = 1.8V
ILOAD = 20mA
L = 22µH, COUT = 47µF
338813 G07
1.2V Output vs Temperature
(LTC3388-1)
1.24
1.22 SLEEP THRESHOLD
1.20
1.18 WAKE-UP THRESHOLD
1.16
1.14
1.12
1.10 PGOOD FALLING
1.08
1.06
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
338813 G08
1.5V Output vs Temperature
(LTC3388-1)
1.54
1.52 SLEEP THRESHOLD
1.50
1.48 WAKE-UP THRESHOLD
1.46
1.44
1.42
1.40
1.38 PGOOD FALLING
1.36
1.34
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
338813 G09
1.8V Output vs Temperature
(LTC3388-1)
1.85
SLEEP THRESHOLD
1.80
WAKE-UP THRESHOLD
1.75
1.70
1.65 PGOOD FALLING
1.60
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
338813 G10
2.5V Output vs Temperature
(LTC3388-1)
2.55
SLEEP THRESHOLD
2.50
WAKE-UP THRESHOLD
2.45
2.40
2.35
2.30 PGOOD FALLING
2.25
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
338813 G11
2.8V Output vs Temperature
(LTC3388-3)
2.90
2.85 SLEEP THRESHOLD
2.80
WAKE-UP THRESHOLD
2.75
2.70
2.65
2.60 PGOOD FALLING
2.55
2.50
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
338813 G12
For more information www.linear.com/LTC3388
338813fa
5
5 Page 
LTC3388-1/LTC3388-3
OPERATION
The LTC3388-1/LTC3388-3 is an ultralow quiescent
current power supply designed to maintain a regulated
output voltage by means of a nanopower high efficiency
synchronous buck regulator.
Undervoltage Lockout (UVLO)
When the voltage on VIN rises above the UVLO rising
threshold the buck converter is enabled and charge is
transferred from the input capacitor to the output ca-
pacitor. If VIN falls below the UVLO falling threshold the
part will re-enter UVLO. In UVLO the quiescent current is
approximately 400nA and the buck converter is disabled.
Internal Rail Generation
Two internal rails, CAP and VIN2, are generated from VIN
and are used to drive the high side PMOS and low side
NMOS of the buck converter, respectively. Additionally the
VIN2 rail serves as logic high for EN, STBY, and output
voltage select bits D0 and D1. The VIN2 rail is regulated
at 4.6V above GND while the CAP rail is regulated at 4.8V
below VIN. The VIN2 and CAP rails are not intended to be
used as external rails. Bypass capacitors are connected
to the CAP and VIN2 pins to serve as energy reservoirs for
driving the buck switches. When VIN is below 4.6V, VIN2
is equal to VIN. CAP is at GND until VIN rises above 4.8V.
Figure 1 shows the ideal VIN, VIN2 and CAP relationship.
18
16
14
VIN
12
10
8
6 VIN2
4
2 CAP
0
0 5 10 15
VIN (V)
338813 F01
Figure 1. Ideal VIN, VIN2 and CAP Relationship
Buck Operation
The buck regulator uses a hysteretic voltage algorithm
to control the output through internal feedback from the
VOUT sense pin. The buck converter charges an output
capacitor through an inductor to a value slightly higher than
the regulation point. It does this by ramping the inductor
current up to 150mA through an internal PMOS switch and
then ramping it down to 0mA through an internal NMOS
switch. This efficiently delivers energy to the output ca-
pacitor. The ramp rate is determined by VIN, VOUT, and the
inductor value. When the buck brings the output voltage
into regulation the converter enters a low quiescent current
sleep state that monitors the output voltage with a sleep
comparator. During this operating mode load current is
provided by the buck output capacitor. When the output
voltage falls below the regulation point the buck regulator
wakes up and the cycle repeats. This hysteretic method
of providing a regulated output reduces losses associated
with FET switching and maintains an output at light loads.
The buck delivers a minimum of 50mA of average load
current when it is switching.
When the sleep comparator signals that the output has
reached the sleep threshold the buck converter may be
in the middle of a cycle with current still flowing through
the inductor. Normally both synchronous switches would
turn off and the current in the inductor would freewheel
to zero through the NMOS body diode. The LTC3388-1/
LTC3388-3 keeps the NMOS switch on during this time to
prevent the conduction loss that would occur in the diode
if the NMOS were off. If the PMOS is on when the sleep
comparator trips, the NMOS will turn on immediately in
order to ramp down the current. If the NMOS is on it will
be kept on until the current reaches zero.
Though the quiescent current when the buck is switching
is much greater than the sleep quiescent current, it is still
a small percentage of the average inductor current which
results in high efficiency over most load conditions. The
buck operates only when the output voltage discharges
to the sleep falling threshold. Thus, the buck operating
quiescent current is averaged with the low sleep quiescent
current. This allows the converter to remain very efficient
at loads as low as 10µA.
For more information www.linear.com/LTC3388
338813fa
11
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet LTC3388-3.PDF ] | |
Hoja de datos destacado
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