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PDF LTC1626CS Data sheet ( Hoja de datos )
| Número de pieza | LTC1626CS | |
| Descripción | Low Voltage/ High Efficiency Step-Down DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC1626
Low Voltage, High Efficiency
Step-Down DC/DC Converter
FEATURES
s Wide Input Supply Voltage Range: 2.5V to 6V
s High Efficiency: Up to 95%
s Low RDS(ON) Internal Switch: 0.32Ω (VIN = 4.5V)
s Current Mode Operation for Excellent Line and Load
Transient Response
s Short-Circuit Protected
s Low Dropout Operation: 100% Duty Cycle
s Built-In Low-Battery Detector
s Low Quiescent Current at Light Loads: IQ = 165µA
s Ultralow Shutdown Current: IQ = 0.5µA
s Peak Inductor Current Independent of Inductor Value
s Available in 14-Pin SO Package
U
APPLICATIONS
s Single Cell Li-Ion Step-Down Converters
s 3- or 4-Cell NiMH Step-Down Converters
s Cellular Telephones
s 5V to 3.3V Conversion
s 3.3V to 2.5V Conversion
s Inverting Converters
s Portable Instruments
DESCRIPTION
The LTC®1626 is a monolithic, low voltage, step-down
current mode DC/DC converter featuring Burst ModeTM
operation at low output current.
The input supply voltage range of 2.5V to 6V makes the
LTC1626 ideal for single cell Li-Ion and 3- or 4-cell NiCd/
NiMH applications. A built-in 0.32Ω switch (VIN = 4.5V)
allows up to 0.6A of output current.
The LTC1626 incorporates automatic power saving Burst
Mode operation to reduce gate charge losses when the
load current drops below the level required for continuous
operation. With no load, the converter draws only 165µA.
In shutdown, it draws a mere 0.5µA—making it ideal for
current sensitive applications.
The inductor current is user-programmable via an external
current sense resistor. In dropout, the internal P-channel
MOSFET switch is turned on continuously, maximizing
battery life.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATION
VIN
2.7V TO 6V
+ CIN†
47µF
16V
0.1µF
PWR VIN
SHDN
VIN
SW
LTC1626
3900pF
470Ω
ITH
PGND
SENSE+
CT
270pF
CT SENSE–
SGND VFB
* COILTRONICS CTX33-4
** IRC 1206-R100F
† AVX TPSD476KO16
†† AVX TPSC107M006R0150
L*
33µH
RSENSE**
0.1Ω
D1
MBRS130LT
+
1000pF
10k
VOUT
2.5V
0.25A
COUT††
100µF
6.3V
100pF
10k
1626 F01
Figure 1. High Efficiency 2.5V Step-Down Converter
100
95
90
85
80
75
70
0.01
Efficiency
VIN = 3.5V
L1 = 33µH
VOUT = 2.5V
RSENSE = 0.1Ω
CT = 270pF
0.1
OUTPUT CURRENT (A)
1
1626 F01a
1
1 page  
U
OPERATIO
The nominal off-time of the LTC1626 is set by an external
timing capacitor connected between the CT pin and ground.
The operating frequency is then determined by the off-
time and the difference between VIN and VOUT.
The output voltage is set by an external divider returned to
the VFB pin. A voltage comparator V and a gain block G
compare the divided output voltage with a reference
voltage of 1.25V.
To optimize efficiency, the LTC1626 automatically switches
between continuous and Burst Mode operation. The volt-
age comparator is the primary control element when the
device is in Burst Mode operation, while the gain block
controls the output voltage in continuous mode.
When the load is heavy, the LTC1626 is in continuous
operation. During the switch “ON” time, current compara-
tor C monitors the voltage between the SENSE + and
SENSE – pins connected across an external shunt in series
with the inductor. When the voltage across the shunt
reaches the comparator’s threshold value, its output sig-
nal changes state, resetting the flip-flop and turning the
internal P-channel MOSFET off. The timing capacitor
connected to the CT pin is now allowed to discharge at a
rate determined by the off-time controller.
When the voltage on the timing capacitor has discharged
past VTH1, comparator T trips, sets the flip-flop and causes
the switch to turn on. Also, the timing capacitor is
recharged. The inductor current will again ramp up until
the current comparator C trips. The cycle then repeats.
When the load current increases, the output voltage
LTC1626
decreases slightly. This causes the output of the gain stage
(Pin 6) to increase the current comparator threshold, thus
tracking the load current.
When the load is relatively light, the LTC1626 automati-
cally switches to Burst Mode operation. The current loop
is interrupted when the output voltage reaches the desired
regulated value. The hysteretic voltage comparator V trips
when VOUT is above the desired output voltage, turning off
the switch and causing the timing capacitor to discharge.
This capacitor discharges past VTH1 until its voltage drops
below VTH2. Comparator S then trips and a sleep signal is
generated. The circuit now enters into sleep mode with the
power MOSFET turned off. In sleep mode, the LTC1626 is
in standby and the load current is supplied by the output
capacitor. All unused circuitry is shut off, reducing quies-
cent current from 1.9mA to 165µA. When the output
capacitor discharges by the amount of the hysteresis of
the comparator V, the P-channel switch turns on again and
the process repeats itself. During Burst Mode operation,
the peak inductor’s current is set at 25mV/RSENSE.
To avoid the operation of the current loop interfering with
Burst Mode operation, a built-in offset VOS is incorporated
in the gain stage. This prevents the current from increas-
ing until the output voltage has dropped below a minimum
threshold.
In dropout, the P-channel MOSFET is turned on continu-
ously (100% duty cycle) providing low dropout operation
with VOUT ≅ VIN.
APPLICATIONS INFORMATION
The basic LTC1626 application circuit is shown in Figure
1. External component selection is driven by the load
requirement and begins with the selection of RSENSE. Once
RSENSE is known, CT and L can be chosen. Next, the
Schottky diode D1 is selected followed by CIN and COUT.
RSENSE Selection for Output Current
RSENSE is chosen based on the required output current.
With the current comparator monitoring the voltage devel-
oped across RSENSE, the threshold of the comparator
determines the peak inductor current. Depending upon
the load current condition, the threshold of the compara-
tor lies between 25mV/RSENSE and 150mV/RSENSE. The
maximum output current of the LTC1626 is:
IOUT(MAX) = 150mV/RSENSE – IRIPPLE/2 (A)
Where IRIPPLE is the peak-to-peak inductor ripple current.
At a relatively light load, the LTC1626 is in Burst Mode
operation. In this mode, the peak current is set at 25mV/
RSENSE. To fully benefit from Burst Mode operation, the
5
5 Page 
TYPICAL APPLICATIONS
Low Profile (3mm Maximum Height) 2.8V Converter
VIN
3V TO 6V
SHUTDOWN
1k
3900pF
CT
56pF
PWR VIN
LBI
LBO
VIN
SW
SHDN
PGND
LTC1626
ITH SENSE+
SENSE –
CT
SGND
VFB
* COILCRAFT DO3308-153
** IRC 1206-R100F
† AVX TPSC226M016R0375
†† AVX TPSC107M006R0150
††† MURATA GRM230Y5V475Z16
4.7µF††† +
CERAMIC
CIN†
22µF
16V
TANT
L1*
15µH
RSENSE**
0.1Ω
D1
MBR0520LT1
1000pF
100pF
LTC1626
VOUT
2.8V
0.25A
+
R1
15k
1%
COUT††
100µF
6.3V
R2
12.1k
1%
1626 TA03
PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted.
S Package
14-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.337 – 0.344*
(8.560 – 8.738)
14 13 12 11 10
9
8
0.228 – 0.244
(5.791 – 6.197)
0.150 – 0.157**
(3.810 – 3.988)
0.010
(0.254
–
–
0.020
0.508)
×
45°
0.008 – 0.010
(0.203 – 0.254)
1234567
0° – 8° TYP
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.016 – 0.050
0.406 – 1.270
0.014 – 0.019
(0.355 – 0.483)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0.050
(1.270)
TYP
S14 0695
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LTC1626CS.PDF ] | |
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