LM3404MA/NOPB National Semiconductor, LM3404MA/NOPB Datasheet - Page 10

• Manufacturer Part Number: LM3404MA/NOPB
• Description: IC LED DRVR HP CONST CURR 8-SOIC
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: High Power, Constant Currentr

Specifications of LM3404MA/NOPB

• Constant Current: Yes
• Topology: PWM, Step-Down (Buck)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Automotive
• Type - Secondary: High Brightness LED (HBLED), White LED
• Frequency: 1MHz
• Voltage - Supply: 6 V ~ 42 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Operating Temperature: -40°C ~ 125°C
• Current - Output / Channel: 1A
• Internal Switch(s): Yes
• Efficiency: 96%
• Current, Input Bias: 0.1 μA
• Current, Output: 1.2 A
• Current, Supply: 625 μA
• Package Type: SOIC
• Regulator Type: Buck (Step-Down), Switching
• Temperature, Operating, Range: -40 to +125 °C
• Time, Fall: 20 ns
• Time, Rise: 20 ns
• Voltage, Input: 6 to 42 V
• Voltage, Output: 7 V
• For Use With: 551600000-001A/NOPB - BOARD WEBENCH SO8/SOP LM3404/2LM3404EVAL - BOARD EVALUATION LM3404
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device
• Other names: *LM3404MA; *LM3404MA/NOPB; LM3404MA; LM3404MATR; LM3404MATR

www.national.com
Block Diagram
Application Information
THEORY OF OPERATION
The LM3404 and LM3404HV are buck regulators with a wide
input voltage range, low voltage reference, and a fast output
enable/disable function. These features combine to make
them ideal for use as a constant current source for LEDs with
forward currents as high as 1.2A. The controlled on-time
(COT) architecture is a combination of hysteretic mode con-
trol and a one-shot on-timer that varies inversely with input
voltage. Hysteretic operation eliminates the need for small-
signal control loop compensation. When the converter runs in
continuous conduction mode (CCM) the controlled on-time
maintains a constant switching frequency over the range of
input voltage. Fast transient response, PWM dimming, a low
power shutdown mode, and simple output overvoltage pro-
tection round out the functions of the LM3404/04HV.
CONTROLLED ON-TIME OVERVIEW
Figure 1
rent through an array of LEDs. A voltage signal, V
created as the LED current flows through the current setting
resistor, R
where it is compared against a 200 mV reference, V
on-comparator turns on the power MOSFET when V
below V
on-time, t
voltage, V
REF
shows the feedback system used to control the cur-
ON
IN
SNS
. The power MOSFET conducts for a controlled
, set by an external resistor, R
. On-time is governed by the following equation:
, to ground. V
SNS
is fed back to the CS pin,
ON
, and by the input
REF
SNS
SNS
. The
falls
, is
10
At the conclusion of t
minimum off-time, t
plete the CS comparator compares V
waiting to begin the next cycle.
The LM3404/04HV regulators should be operated in contin-
uous conduction mode (CCM), where inductor current stays
positive throughout the switching cycle. During steady-state
FIGURE 1. Comparator and One-Shot
OFF-MIN
ON
the power MOSFET turns off for a
, of 300 ns. Once t
SNS
and V
20205405
OFF-MIN
REF
20205403
is com-
again,