LM3407EVAL National Semiconductor, LM3407EVAL Datasheet - Page 10

• Manufacturer Part Number: LM3407EVAL
• Description: BOARD EVALUATION FOR LM3407
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3407EVAL

• Current - Output / Channel: 350mA
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 4.5V
• Features: Dimmable
• Voltage - Input: 4.5 ~ 30V
• Utilized Ic / Part: LM3407
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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INTERNAL VCC REGULATOR
The LM3407 has an internal 4.5V linear regulator. This regu-
lated voltage is used for powering the internal circuitry only
and any external loading at the VCC pin is not recommended.
The supply input (V
voltage up to 30V. The VCC pin provides voltage regulated at
4.5V for V
nected to VCC pin directly by an internal bypassing switch.
For stability reason, an external capacitor C
680 nF (1 µF recommended) must be connected to the VCC
pin.
CLOCK GENERATOR
The LM3407 features an integrated clock generator to control
the switching frequency of the converter, f
sistor R
the switching frequency. The oscillator frequency can be set
in the range of 300 kHz to 1 MHz. The relationship between
the frequency setting resistance and the oscillator frequency
is described in the Application Information Section.
FS
, connected to the FS pin and ground, determines
IN
≤
6V. For 4.5V
IN
) can be connected directly to an input
FIGURE 5. Waveforms of V
≤
V
IN
FIGURE 4. Implementation of the PWM Switching Signal
≤
6V, VIN pin will be con-
SW
VCC
. An external re-
with at least
ISNS
and V
10
RP
PWM DIMMING OF LED STRING
Dimming of LED brightness is achieved by Pulse Width Mod-
ulation (PWM) control of the LED current. Pulse Width Mod-
ulation control allows LED brightness to be adjusted while still
maintaining accurate LED color temperature. The LM3407
accepts an external PWM dimming signal at the DIM pin. The
signal is buffered before being applied to the internal switch
control block responsible for controlling the ON/OFF of the
power switch, Q1. The DIM pin is internally pulled low by a
resistor and no LED current will be available when the DIM
pin is floating or shorted to ground. Functionally, the DIM pin
can also be used as an external device disable control. Device
switching will be disabled if the DIM pin is not connected or
tied to ground.
LOW POWER SHUTDOWN MODE
The LM3407 comes with a dedicated device enable pin, EN,
for low power shutdown of the device. By putting the device
in shutdown mode, most of the internal circuits will be disabled
and the input current will reduced to below typically 50µA. The
Under Closed Loop Operation
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