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PDF LTC7820 Data sheet ( Hoja de datos )
| Número de pieza | LTC7820 | |
| Descripción | Fixed Ratio High Power Inductorless (Charge Pump) DC/DC Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC7820
Features
Fixed Ratio High Power
Inductorless (Charge Pump)
DC/DC Controller
Description
nn Low Profile, High Power Density, Capable of 500W+
nn Soft Switching: 99% Peak Efficiency and Low EMI
nn VIN Max for Voltage Divider (2:1): 72V
nn VIN Max for Voltage Doubler (1:2)/Inverter (1:1): 36V
nn Wide Bias VCC Range: 6V to 72V
nn Soft Startup into Steady State Operation
nn 6.5V to 40V EXTVCC Input for Improved Efficiency
nn Input Current Sensing and Overcurrent Protection
nn Wide Operating Frequency Range: 100kHz to 1MHz
nn Output Short-Circuit/OV/UV Protections with
Programmable Timer and Retry
nn Thermally Enhanced 28-Pin 4mm × 5mm QFN Package
Applications
nn Bus Converters
nn High Power Distributed Power Systems
nn Communications Systems
nn Industrial Applications
The LTC®7820 is a fixed ratio high voltage high power
switched capacitor/charge pump controller. The device
includes four N-channel MOSFET gate drivers to drive
external power MOSFETs in voltage divider, doubler or
inverter configurations. The device achieves a 2:1 step-
down ratio from an input voltage as high as 72V, a 1:2
step-up ratio from an input voltage as high as 36V, or a
1:1 inverting ratio from an input voltage up to 36V. Each
power MOSFET is switched with 50% duty cycle at a
constant pre-programmed switching frequency. System
efficiency can be optimized to over 99%. The LTC7820
provides a small and cost effective solution for high
power, non-isolated intermediate bus applications with
fault protection.
The LTC7820 switching frequency can be linearly
programmed from 100 kHz to 1MHz. The device is available
in a thermally enhanced 28-lead QFN package with some
no-connect pins for high voltage compatible pin spacing.
L, LT, LTC, LTM, Linear Technology, the Linear logo and LTspice are registered trademarks of
Analog Devices, Inc. All other trademarks are the property of their respective owners. Protected
by U.S. patents, including 9484799.
Typical Application
Very High Efficiency 5A Voltage Divider
10Ω
0.1µF
100Ω
0.1µF
0.1µF
VHIGH_SENSE
VCC
ISENSE–
G1
ISENSE+
TIMER
BOOST1
LTC7820
SW1
G2
RUN BOOST2
12V
INTVCC
10k
10k
10k
10k 40k
EXTVCC
UV
HYS_PRGM
PGOOD
FREQ
VLOW
VLOW_SENSE
G3
BOOST3
SW3
G4
INTVCC
FAULT
GND
0.1µF
1µF
1µF
INTVCC
4.7µF
RSENSE
0.005Ω
VIN
48V/24V
10Ω
0.1µF
10µF
×6
10µF
VOUT
24V/12V
5A*
* LOAD CURRENT APPLIED
AFTER STARTUP
7820 TA01a
Efficiency and Power Loss
vs Load Current
100
EFFICIENCY
99
VIN = 48V
VOUT = 24V
2.0
1.6
98
fs = 100kHz
97
96
1.2
VIN = 24V
VOUT = 12V
0.8
0.4
POWER LOSS
95 0
012345
LOAD CURRENT (A)
7820 TA01b
7820f
For more information www.linear.com/LTC7820
1
1 page  
LTC7820
Typical Performance Characteristics TA = 25°C, unless otherwise noted.
Efficiency vs Load Current
48V to 24V Voltage Divider in
Figure 7
100.0
99.5
99.0
98.5
98.0
97.5
97.0
96.5
96.0
fS = 150kHz
fS = 200kHz
95.5
fS = 250kHz
fS = 300kHz
95.0
1 3 5 7 9 11 13 15
LOAD CURRENT (A)
7820 G01
Efficiency vs Load Current
24V to 12V Voltage Divider in
Figure 7
100.0
99.5
99.0
98.5
98.0
97.5
97.0
96.5
96.0
fS = 150kHz
fS = 200kHz
95.5
fS = 250kHz
fS = 300kHz
95.0
1 3 5 7 9 11 13 15
LOAD CURRENT (A)
7820 G02
Efficiency vs Load Current
24V to 48V Voltage Doubler in
Figure 8
100.0
99.5
99.0
98.5
98.0
97.5
97.0
96.5
96.0
fS = 150kHz
fS = 200kHz
95.5
fS = 250kHz
fS = 300kHz
95.0
0.5 1.5 2.5 3.5 4.5 5.5 6.5 7.5
LOAD CURRENT (A)
7820 G03
Efficiency vs Load Current
24V to –24V Inverter in Figure 9
98.0
97.5
97.0
96.5
96.0
95.5
95.0
94.5
94.0
93.5
93.0
0
fS = 150kHz
fS = 200kHz
fS = 250kHz
fS = 300kHz
2 4 6 8 10
LOAD CURRENT (A)
7820 G04
Output Voltage vs Load Current
48V to 24V Voltage Divider in
Figure 7
24.05
24.00
23.95
23.90
fS = 150kHz
fS = 200kHz
fS = 250kHz
fS = 300kHz
23.85
23.80
23.75
23.70
23.65
23.60
23.55
–1 1
3 5 7 9 11
LOAD CURRENT (A)
13 15
7820 G05
Output Voltage vs Load Current
24V to 48V Voltage Doubler in
Figure 8
48.1
48.0
fS = 150kHz
fS = 200kHz
47.9
fS = 250kHz
fS = 300kHz
47.8
47.7
47.6
47.5
47.4
47.3
47.2
47.1
012345678
LOAD CURRENT (A)
7820 G06
Output Voltage vs Load Current
24V to –24V Inverter in Figure 9
–22.8
Steady State Output Ripple
in Figure 7
–23.0
–23.2
–23.4
–23.6
–23.8
–24.0
–24.2
0
150kHz
200mV/DIV
AC-COUPLED
200kHz
200mV/DIV
AC-COUPLED
250kHz
200mV/DIV
AC-COUPLED
fS = 150kHz
fS = 200kHz
fS = 250kHz
fS = 300kHz
2 4 6 8 10
LOAD CURRENT (A)
7820 G07
VIN = 48V
VOUT = 24V
ILOAD = 10A
10µs/DIV
Load Transient 0A-10A-0A
48V to 24V Divider in Figure 7
fS = 250kHz
VOUT
200mV/DIV
AC-COUPLED
7820 G08
ILOAD
5A/DIV
50µs/DIV
7820 G09
For more information www.linear.com/LTC7820
7820f
5
5 Page 
LTC7820
Applications Information
The Typical Application on the first page of this data sheet
is a LTC7820 voltage divider circuit. For voltage divider
applications, the input voltage is at the drain of very top
MOSFET M1 and the output voltage is at the VLOW pin,
which is connected to the source of MOSFET M2 and the
drain of MOSFET M3. The output voltage is around half
of the input voltage in steady state. Alternately, by swap-
ping the input and output voltages, the voltage divider
circuit can be transformed into a voltage doubler circuit.
For voltage doubler applications, the input voltage is at
the VLOW pin while output voltage is available at the drain
of the top MOSFET M1 and equals two times the input
voltage as shown in Figure 8. Similarly, for inverter ap-
plications, the input voltage is applied between the drain
of the top MOSFET M1 and VLOW, and the output voltage
equals the negative input voltage at the GND pin with
respect to the VLOW pin as shown in Figure 9. For divider
applications, if the load current is applied before startup or
heavy resistive loads are connected to the VLOW pin, the
LTC7820 may not start up due to the limited drive ability
of the pre-balance circuit. A disconnect FET may be used
at the output for soft-start up. For doubler and inverter
applications, a disconnect FET may also be required for
soft start-up and shutdown. The disconnect FETs in divider/
doubler/inverter applications may be also controlled by
hot swap controllers to achieve more programmable slew
rates and fault protections.
Voltage Divider Pre-Balance before Switching
In voltage divider applications, the VLOW_SENSE voltage
should be always close to VHIGH_SENSE/2 in steady state.
The voltages across the flying capacitors and VLOW ca-
pacitors are close to each other and close to half of the
input voltage. The charging inrush current is minimized
during each switching cycle because the voltage difference
between capacitors is small. However, without special
methods such as the LTC7820 pre-charging circuitry,
during start-up or fault conditions such as VLOW short to
GND, the difference between capacitors can be large and
charging currents may be great enough to cause permanent
MOSFET damage.
When the power MOSFETs are on, ideally, the inrush
charge current,
I
=
VIN – VCFLY – VLOW
RON _ M1 + RON _ M3
when switches M1 and M3 are on and:
I
=
VCFLY
RON _ M2
–
+
VLOW
RON _ M4
when switches M2 and M4 are on. Both currents are lim-
ited by the power MOSFET saturation current. With very
low RDS(ON) of the external power MOSFETs, the inrush
charge current could easily achieve several hundreds of
Amperes which can be higher than the MOSFET’s Safe
Operating Area (SOA).
The LTC7820 provides a proprietary pre-balance method
to minimize the inrush charging current in voltage
divider applications. The LTC7820 controller detects the
VLOW_SENSE pin voltage before switching and compares
it with the VHIGH_SENSE/2 internally. If the VLOW_SENSE pin
voltage is much lower than the VHIGH_SENSE/2, a current
source will source 93mA current to the VLOW pin to pull
the VLOW pin up. If the VLOW_SENSE pin voltage is much
higher than the VHIGH_SENSE/2, another current source
will sink 50mA from VLOW pin to pull the VLOW pin down.
If the VLOW_SENSE pin voltage is close to VHIGH_SENSE/2
and within the pre-programmed window, both current
sources are disabled and LTC7820 starts switching. If
the VLOW_SENSE voltage is still within the window after 68
switching cycles, the FAULT pin is released.
For voltage divider with pre-balance startup, the LTC7820
assumes no load current or a very small load current (less
than 50mA) at the VLOW (output) otherwise the VLOW volt-
age cannot reach VHIGH_SENSE/2 and the LTC7820 never
starts up. This no load condition can be achieved by con-
necting the FAULT pin to the enable pins of the following
electrical loads such as switching regulators and LDOs.
If load current cannot be controlled off such as resistive
loads, a disconnect FET is required to disconnect the load
during startup as shown in the typical applications.
For more information www.linear.com/LTC7820
7820f
11
11 Page | ||
| Páginas | Total 26 Páginas | |
| PDF Descargar | [ Datasheet LTC7820.PDF ] | |
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