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PDF LTC3832-1 Data sheet ( Hoja de datos )
| Número de pieza | LTC3832-1 | |
| Descripción | High Power Step-Down Synchronous DC/DC Controllers for Low Voltage Operation | |
| Fabricantes | Linear Technology | |
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LTC3832/LTC3832-1
High Power Step-Down
Synchronous DC/DC Controllers
for Low Voltage Operation
FEATURES
s VOUT as Low as 0.6V
s High Power Switching Regulator Controller
for 3.3V-5V to 0.6V-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 2.5V Output (LTC3832)
s Programmable Fixed Frequency Operation: 100kHz to
500kHz
s External Clock Synchronization
s Soft-Start
s Low Shutdown Current: <10µA
s Overtemperature Protection
s Available in SO-8 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®3832/LTC3832-1 are high power, high effi-
ciency switching regulator controllers optimized for
3.3V-5V to 0.6V-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 LTC3832/LTC3832-1 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 MOSFET, providing an adjustable current limit
without a current sense resistor.
The LTC3832/LTC3832-1 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 300kHz
free-running clock frequency can be externally adjusted or
synchronized with an external signal from 100kHz to 500kHz.
In shutdown mode, the LTC3832 supply current drops to
<10µA. The LTC3832-1 is the SO-8 version without current
limit, frequency adjustment and shutdown functions.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
4.7µF
0.1µF
0.01µF
LTC3832-1
SS VCC/PVCC2
COMP
G1
15k
6.49k
GND PVCC1
FB G2
5.1Ω
VIN
3V TO 7V
+
MBR0520T1
0.1µF
Si9426DY L1
3.2µH
Si9426DY
+
4.32k
680pF
L1: SUMIDA CDEP105-3R2MC-88
COUT: PANASONIC EEFUEOD271R
VOUT
1V
9A
COUT
270µF
2V
3832 F01
Figure 1. High Efficiency 3.3V to 1V Power Converter
Efficiency
100
90 VOUT = 2.5V
80 VOUT = 1V
70
60
50
VIN = 3.3V
40
0 1 2 3 4 5 6 7 8 9 10
LOAD CURRENT (A)
3832 F01b
sn3832 3832fs
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC3832/LTC3832-1
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
3832 G10
Output Current Limit Threshold
vs Temperature
20
REFER TO FIGURE 12 AND NOTE 10 OF
19 THE ELECTRICAL CHARACTERISTICS
18
17
16
15
14
13
12
11
10
–50 –25
0 25 50 75 100 125
TEMPERATURE (°C)
3832 G13
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)
3832 G16
IMAX Sink Current
vs Temperature
20
18
16
14
12
10
8
6
4
– 50 – 25
0 25 50 75
TEMPERATURE (°C)
100 125
3832 G11
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 G14
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
3832 G17
Output Overcurrent Protection
3.0
TA = 25°C
REFER TO FIGURE 12
2.5
2.0
1.5
1.0
0.5
0
0 2 4 6 8 10 12 14 16 18 20
OUTPUT CURRENT (A)
3832 G12
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
3832 G15
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)
3832 G18
sn3832 3832fs
5
5 Page 
LTC3832/LTC3832-1
APPLICATIO S I FOR ATIO
Connecting a 82k resistor from FREQSET to ground
forces 15µA out of the pin, causing the internal oscillator
to run at approximately 450kHz. Forcing an external 20µA
current into FREQSET cuts the internal frequency to
100kHz. An internal clamp prevents the oscillator from
running slower than about 50kHz. Tying FREQSET to VCC
forces the chip to run at this minimum speed. The
LTC3832-1 does not have this frequency adjustment
function.
Shutdown
The LTC3832 includes a low power shutdown mode,
controlled by the logic at the SHDN pin. A high at SHDN
allows the part to operate normally. A low level at SHDN for
more than 100µs forces the LTC3832 into shutdown
mode. In this mode, all internal switching stops, the COMP
and SS pins pull to ground and Q1 and Q2 turn off. The
LTC3832 supply current drops to <10µA, although off-
state leakage in the external MOSFETs may cause the total
VIN current to be some what higher, especially at elevated
temperatures. If SHDN returns high, the LTC3832 reruns
a soft-start cycle and resumes normal operation. The
LTC3832-1 does not have this shutdown function.
Figure 5 describes the operation of the conventional
synchronization function. A negative transition at the
SHDN pin forces the internal ramp signal low to restart a
new PWM cycle. Notice that 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 feed-
back loop to be unstable if the phase margin is insufficient.
To overcome this problem, the LTC3832 monitors the
peak voltage of the ramp signal and adjusts the oscillator
charging current to maintain a constant ramp peak.
SHDN
300kHz
FREE RUNNING
RAMP SIGNAL
TRADITIONAL
SYNC METHOD
WITH EARLY
RAMP
TERMINATION
RAMP SIGNAL
WITH EXT SYNC
External Clock Synchronization
The LTC3832 SHDN pin doubles as an external clock
input for applications that require a synchronized clock.
An internal circuit forces the LTC3832 into external
synchronization mode if a negative transition at the SHDN
pin is detected. In this mode, every negative transition on
the SHDN pin resets the internal oscillator and pulls the
ramp signal low, this forces the LTC3832 internal oscil-
lator to lock to the external clock frequency. The LTC3832-1
does not have this external synchronization function.
The LTC3832 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 LTC3832 enters shutdown
mode.
RAMP AMPLITUDE
ADJUSTED
LTC3832
KEEPS RAMP
AMPLITUDE
CONSTANT
UNDER SYNC
Figure 5. External Synchronization Operation
3832 F05
Input Supply Considerations/Charge Pump
The LTC3832 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 LTC3832
internal circuitry (Figure 6). The LTC3832-1 has 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 LTC3832, but must also be able
to supply the gate drive current to Q2.
sn3832 3832fs
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3832-1.PDF ] | |
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