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PDF LM2648 Data sheet ( Hoja de datos )

Número de pieza LM2648
Descripción Synchronous Step-Down 3-Channel Switching Regulator Controller
Fabricantes National Semiconductor 
Logotipo National Semiconductor Logotipo



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No Preview Available ! LM2648 Hoja de datos, Descripción, Manual

December 2004
LM2648
Two-Phase, Synchronous Step-Down 3-Channel
Switching Regulator Controller
General Description
The LM2648 consists of two current mode and two voltage
mode synchronous buck regulator controllers providing 3
outputs at a switching frequency of 300kHz.
Each pair of switching regulator controllers operate 180˚ out
of phase. This feature reduces the input ripple RMS current,
thereby significantly reducing the required input capacitance.
The two current mode regulator outputs operate as a dual-
phase, single output regulator for high current applications.
Current-mode feedback control on Channel 3 assures supe-
rior line and load regulation and wide loop bandwidth as-
sures excellent response to fast load transients. Channels 1
and 2 employ voltage-mode feedback control.
The LM2648 features analog soft-start circuitry that is inde-
pendent of the output load and output capacitance. This
makes the soft-start behavior more predictable than tradi-
tional soft-start circuits. Sequential startup is built in and
requires a single capacitor to set the timing.
The LM2648 has over-voltage protection and under-voltage
protection for all outputs. Two additional comparator inputs
(analog and logic level) are provided to shut down the IC for
any user defined protection. The FAULT_DELAY pin allows
delayed shut off time for the IC during an under-voltage or
PROT-IN2 fault. The LM2648 also features an adjustable
UVLO feature.
Features
n Four synchronous buck regulators
n Channel 3: Two-phase, current mode controller
n 4.5V to 18V input range
n Built in sequential startup
n Channels 1 and 2: Independent, 180˚ out of phase
voltage mode controllers
n Single soft start for channels 1 and 2
n Adjustable cycle-by-cycle current limit for each channel
n Adjustable reference current
n Adjustable input under-voltage lockout
n Output over-voltage latch protection
n Output under-voltage protection with delay
n Two comparator inputs for user defined protection - one
with delay
n Thermal shutdown
n Self-discharge of output capacitors when the regulator is
off
n TSSOP package
Applications
n Embedded Computer Systems
n Interactive Games
n Set-top Boxes/Home Gateways
Block Diagram
© 2004 National Semiconductor Corporation DS200596
20059690
www.national.com

1 page




LM2648 pdf
Electrical Characteristics (Continued)
Unless otherwise specified, VIN = 12V, SGND = PGND = 0V, VLIN5 = VDD1 = VDD2 = VDD3x. Limits appearing in boldface
type apply over the full operating junction temperature range. Specifications appearing in plain type are measured using low
duty cycle pulse testing with TA = 25˚C (Note 5), (Note 6). Min/Max limits are guaranteed by design, test, or statistical analysis.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
ISK_TD12-3
Delay Timer Sink
Current
VTD = 0.4V
192 274 356
µA
VTD12-3
Delay Timer Threshold
Voltage
Rising
1.70
1.94
2.20
V
Iss1/2_sc/
Iss3_sc
Iss1/2_sc/
Isc_TD12-3
Shutdown
Soft-Start Source
Current Ratio
Soft-Start to Delay Timer
Source Current Ratio
-13%
-32%
1.0
0.209
+13%
+32%
A/A
A/A
VStandby
Standby Threshold
(ON/UVLO pin)
Rising
Shutdown to Standby
0.95 1.2 1.44
V
Hysteresis
149 mV
VON ON Threshold
Rising
(ON/UVLO pin)
Standby to On
1.75
1.98
2.20
V
Hysteresis
205 mV
SW_ R1, 2
SW_R3a, 3b
SW1, 2 ON Resistance
SW3a, 3b ON
Resistance
VSW1 = VSW2 = 0.4V
VSW3a = VSW3b = 0.4V
440 570 700
200 249 310
VSW_dis
SW3a Quick Discharge LDRV3a = High
Threshold at FB3 (falling
.81 V
edge)
Protection
ISC_FAULTDELAY FAULT_DELAY source
current
FAULT_DELAY = 2.0V
3.54
4.7
5.9
µA
ISK_FAULTDELAY FAULT_DELAY sink
current
FAULT_DELAY = 0.4V
0.27
mA
VFAULT_DELAY FAULT_DELAY
threshold Voltage
Rising
1.75
1.96
2.20
V
VUVP
FB1, 2, 3 Under Voltage As a percentage of nominal output
Protection Latch
voltage (falling edge)
75 80.6 86
%
Threshold
Hysteresis
4%
VOVP
FB1, 2, 3 Over-voltage
Shutdown Latch
As a percentage of nominal output
voltage (rising edge)
106 112 119
%
Threshold
VUVLO_INT
VLIN5 Under Voltage
Lockout Threshold
Rising
4.2 V
Hysteresis
8%
VPROT-IN1
Analog protection
threshold
1.19
1.239
1.4
V
VPROT-IN2
Logic protection
threshold
0.8 1.48
2
V
Isk_prot-in2
Gate Drive
PROT-IN2 sink current
2 µA
ICBOOT
CBOOTx Leakage
Current
VCBOOTX = 7V
10 nA
ISC_DRV
HDRVx and LDRVx
Source Current
HDRV = LDRV = 2.5V
0.5 A
Isk_HDRV
HDRVx Sink Current
HDRVX = 2.5V
0.8 A
5 www.national.com

5 Page





LM2648 arduino
Typical Performance Characteristics
Efficiency vs Load Current
Ch.1 = 5V, Ch.2 = 3.3V, VIN = 12V, Ch.1/2/3: ON
Efficiency vs Load Current
Ch.3 = 1.9V, VIN = 12V, Ch.1/2/3: ON
20059664
FB Voltage vs Temperature
20059665
Input Supply Current vs Temp. Shutdown Mode
20059666
Input Supply Current vs VIN Shutdown Mode
20059667
FB3 Quick Discharge Threshold Voltage vs Temperature
20059668
11
20059669
www.national.com

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