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PDF LTC3830 Data sheet ( Hoja de datos )
| Número de pieza | LTC3830 | |
| Descripción | High Power Step-Down Synchronous DC/DC Controllers for Low Voltage Operation | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3830/LTC3830-1
High Power Step-Down
Synchronous DC/DC Controllers
for Low Voltage Operation
FEATURES
s High Power Switching Regulator Controller
for 3.3V-5V to 1.xV-3.xV Step-Down Applications
s No Current Sense Resistor Required
s Low Input Supply Voltage Range: 3V to 8V
s Maximum Duty Cycle > 91% Over Temperature
s All N-Channel External MOSFETs
s Excellent Output Regulation: ±1% Over Line, Load
and Temperature Variations
s High Efficiency: Over 95% Possible
s Adjustable or Fixed 3.3V Output (16-Pin Version)
s Programmable Fixed Frequency Operation: 100kHz to
500kHz
s External Clock Synchronization
s Soft-Start (Some Versions)
s Low Shutdown Current: <10µA
s Overtemperature Protection
s Available in S8, S16 and SSOP-16 Packages
U
APPLICATIO S
s CPU Power Supplies
s Multiple Logic Supply Generator
s Distributed Power Applications
s High Efficiency Power Conversion
DESCRIPTIO
The LTC®3830/LTC3830-1 are high power, high effi-
ciency switching regulator controllers optimized for
3.3V-5V to 1.xV-3.xV step-down applications. A preci-
sion internal reference and feedback system provide
±1% output regulation over temperature, load current
and line voltage variations. The LTC3830/LTC3830-1 use
a synchronous switching architecture with N-channel
MOSFETs. Additionally, the chip senses output current
through the drain-source resistance of the upper
N-channel FET, providing an adjustable current limit
without a current sense resistor.
The LTC3830/LTC3830-1 operate with an input supply
voltage as low as 3V and with a maximum duty cycle of
>91% over temperature. They include a fixed frequency
PWM oscillator for low output ripple operation. The 200kHz
free-running clock frequency can be externally adjusted or
synchronized with an external signal from 100kHz to 500kHz.
In shutdown mode, the LTC3830 supply current drops to
<10µA. The LTC3830-1 differs from the LTC3830 S8 ver-
sion by replacing shutdown with a soft-start function.
For a similar, pin compatible DC/DC converter with an
output voltage as low as 0.6V, please refer to the LTC3832.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
4.7µF
VIN
3V TO 8V
5.1Ω
0.1µF
0.01µF
15k
12.7k 1%
LTC3830-1
SS PVCC2
COMP G1
GND PVCC1
FB G2
5.36k 1%
12V
4.7µF
+ 220µF
10V
M1
Si7806DN
L
3.2µH
M2
Si7806DN
B320A +
3.3nF
L: SUMIDA CDEP105-3R2MC-88
COUT: PANASONIC EEFUEOD271R
1.8V
9A
COUT
270µF
2V
3830 F01
Figure 1. High Efficiency 3V-8V to 1.8V Power Converter
Efficiency
100
VIN = 3.3V
VOUT = 1.8V
90
80
70
60
50
40
0 1 2 3 4 5 6 7 8 9 10
LOAD CURRENT (A)
3830 TA02
sn3830 3830fs
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC3830/LTC3830-1
Maximum G1 Duty Cycle
vs Temperature
100
VFB = 0V
99 REFER TO FIGURE 3
98
97
96
95
94
93
92
91
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3830 G11
Output Current Limit Threshold
vs Temperature
15
REFER TO FIGURE 12 AND NOTE 10 OF
14 THE ELECTRICAL CHARACTERISTICS
13 RIMAX = 20k
12
11
10
9
8
7
6
5
–50 –25
0 25 50 75 100 125
TEMPERATURE (°C)
3830 G14
Undervoltage Lockout Threshold
Voltage vs Temperature
3.0
2.9
2.8
2.7
2.6
2.5
2.4
2.3
2.2
2.1
2.0
–50 –25
0 25 50 75 100 125
TEMPERATURE (°C)
3830 G17
IMAX Sink Current
vs Temperature
20
18
16
14
12
10
8
6
4
– 50 – 25
0 25 50 75
TEMPERATURE (°C)
100 125
3830 G12
Soft-Start Source Current
vs Temperature
–8
–9
–10
–11
–12
–13
–14
–15
–16
– 50 – 25
0 25 50 75
TEMPERATURE (°C)
100 125
3830 G15
VCC Operating Supply Current
vs Temperature
1.6
FREQSET FLOATING
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3830 G18
Output Overcurrent Protection
3.5
3.0 TA = 25°C
REFER TO FIGURE 12
2.5 RIMAX = 20k
2.0
1.5
1.0
0.5
0
0 2 4 6 8 10 12 14
OUTPUT CURRENT (A)
3830 G13
Soft-Start Sink Current
vs (VIFB – VIMAX)
2.00
TA = 25°C
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
–150 –125 –100 –75 –50
VIFB – VIMAX (mV)
–25 0
3830 G16
PVCC Supply Current
vs Oscillator Frequency
90
TA = 25°C
80
70
60
G1 AND G2 LOADED
WITH 6800pF,
PVCC1,2 = 12V
50 G1 AND G2
40
LOADED
WITH 1000pF,
30 PVCC1,2 = 5V
G1 AND G2
LOADED
WITH 6800pF,
PVCC1,2 = 5V
20
10
0
0 100 200 300 400 500
OSCILLATOR FREQUENCY (kHz)
3830 G19
sn3830 3830fs
5
5 Page 
LTC3830/LTC3830-1
APPLICATIO S I FOR ATIO
The LTC3830 internal oscillator can be externally synchro-
nized from 100kHz to 500kHz. Frequencies above 300kHz
can cause a decrease in the maximum obtainable duty
cycle as rise/fall time and propagation delay take up a
larger percentage of the switch cycle. Circuits using these
frequencies should be checked carefully in applications
where operation near dropout is important—like 3.3V to
2.5V converters. The low period of this clock signal must
not be >100µs, or else the LTC3830 enters shutdown
mode.
Figure 5 describes the operation of the external synchro-
nization function. A negative transition at the SHDN pin
forces the internal ramp signal low to restart a new PWM
cycle. Notice that with the traditional sync method, the
ramp amplitude is lowered as the external clock frequency
goes higher. The effect of this decrease in ramp amplitude
increases the open-loop gain of the controller feedback
loop. As a result, the loop crossover frequency increases
and it may cause the feedback loop to be unstable if the
phase margin is insufficient.
To overcome this problem, the LTC3830 monitors the
peak voltage of the ramp signal and adjusts the oscillator
charging current to maintain a constant ramp peak.
Input Supply Considerations/Charge Pump
The 16-lead LTC3830 requires four supply voltages to
operate: VIN for the main power input, PVCC1 and PVCC2 for
MOSFET gate drive and a clean, low ripple VCC for the
LTC3830 internal circuitry (Figure 6). The LTC3830-1 and
the 8-lead LTC3830 have the PVCC2 and VCC pins tied
together inside the package (Figure 7). This pin, brought
out as VCC/PVCC2 , has the same low ripple requirements
as the 16-lead part, but must also be able to supply the gate
drive current to Q2.
In many applications, VCC can be powered from VIN
through an RC filter. This supply can be as low as 3V. The
low quiescent current (typically 800µA) allows the use of
relatively large filter resistors and correspondingly small
VCC PVCC2 PVCC1
VIN
SHDN
200kHz
FREE RUNNING
TRADITIONAL RAMP SIGNAL
SYNC METHOD
WITH EARLY
RAMP
TERMINATION
RAMP SIGNAL
WITH EXT SYNC
INTERNAL
CIRCUITRY
LTC3830 (16-LEAD)
G1
Q1
LO
VOUT
G2
Q2
+
COUT
3830 F6
Figure 6. 16-Lead Power Supplies
VCC/PVCC2
PVCC1
VIN
RAMP AMPLITUDE
ADJUSTED
LTC3830
KEEPS RAMP
AMPLITUDE
CONSTANT
UNDER SYNC
Figure 5. External Synchronization Operation
3830 F05
INTERNAL
CIRCUITRY
LTC3830 (8-LEAD)
G1
Q1
LO
VOUT
G2
Q2
+
COUT
3830 F7
Figure 7. 8-Lead Power Supplies
sn3830 3830fs
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3830.PDF ] | |
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