LM3554TME/NOPB National Semiconductor, LM3554TME/NOPB Datasheet - Page 16

• Manufacturer Part Number: LM3554TME/NOPB
• Description: IC LED DVR PHOTO FLASH 16-USMD
• Manufacturer: National Semiconductor
• Type: Photo Flash LED (I²C Interface)r

Specifications of LM3554TME/NOPB

• Constant Current: Yes
• Topology: High Side, Step-Up (Boost)
• Number Of Outputs: 2
• Internal Driver: Yes
• Type - Primary: Flash/Torch
• Type - Secondary: White LED
• Frequency: 2MHz
• Voltage - Supply: 2.7 V ~ 5.5 V
• Voltage - Output: 5V
• Mounting Type: Surface Mount
• Package / Case: 16-MicroSMD
• Operating Temperature: -30°C ~ 85°C
• Current - Output / Channel: 600mA
• Internal Switch(s): Yes
• Efficiency: 90%
• Led Driver Application: LED Backlighting, Portable Electronics
• No. Of Outputs: 2
• Output Current: 1.2A
• Input Voltage: 2.7V To 5.5V
• Dimming Control Type: I2C
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM3554TMETR

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Flash pulse is forced to the Torch current setting, or into shut-
down depending on the NTC Shutdown bit setting .
Control of the LM3554 is done via an I
face. This includes switch-over from LED to Voltage Output
mode, adjustment of the LED current in TORCH mode, ad-
justment of the LED current in FLASH mode, adjustment of
the indicator LED currents, changing the flash LED current
duration, changing the switch current limit. Additionally, there
are 5 flag bits that can be read back indicating flash current
timeout, over-temperature condition, LED failure (open or
short), LED thermal failure, and an input voltage fault.
STARTUP
Turn on of the LM3554 is done through bits [2:0] of the Torch
Brightness Register (0xA0), bits [2:0] of the Flash Brightness
Register (0xB0), the ENVM input, or the STROBE input. Bits
[1:0] of the Torch Brightness Register or Flash Brightness
Register enables/disables the current sources (LED1, LED2,
and LEDI). Bit [2] enables/disables the voltage output mode.
A logic high at STROBE enables Flash mode. A logic high on
the ENVM input forces the LM3554 into Voltage Output mode.
On startup, when V
chronous PFET turns on as a current source and delivers
typically 350mA to the output capacitor. During this time all
current sources (LED1, LED2, and LEDI) are off. When the
voltage across the output capacitor reaches 2.2V, the current
sources can turn on. At turn-on the current sources step
through each FLASH or TORCH level until the target LED
current is reached (16 µs/step). This gives the device a con-
trolled turn-on and limits inrush current from the V
PASS MODE
Once the Output voltage charges up to V
LM3554 will decide if the part operates in Pass Mode or Boost
mode. If the voltage difference between V
than 300mV, the device will transition in Boost Mode. If the
difference between V
device will operate in Pass Mode. In Pass Mode the boost
converter stops switching, and the synchronous PFET turns
fully on bringing V
150mΩ). In Pass Mode the inductor current is not limited by
the peak current limit. In this situation the output current must
be limited to 2.5A.
LIGHT LOAD DISABLE
Configuration Register 1 bit [0] = 1 disables the light load
comparator. With this bit set to 0 (default) the light load com-
parator is enabled. Light Load mode only applies when the
LM3554 is active in Voltage Output mode. In LED mode the
Light Load Comparator is always disabled. When the light
OUT
OUT
OUT
and V
up to V
is less than V
LED
IN
is greater than 300mV, the
– I
IN
2
IN
OUT
C-compatible inter-
×R
the internal syn-
IN
PMOS
and V
- 150mV the
IN
LED
(R
supply.
PMOS
is less
=
16
load comparator is disabled the LM3554 will operate at a con-
stant frequency down to I
useful when a more predictable switching frequency across
the entire load current range is desired.
VOLTAGE OUTPUT MODE
Bit 2 (VM) of the Torch Brightness Register, bit 2 (VM) of the
Flash Brightness Register, or the ENVM input enables or dis-
ables the Voltage Output mode. In Voltage Output mode the
device operates as a simple boost converter with two se-
lectable voltage levels (4.5V and 5V). Write a (1) to bit 1 (OV)
of Configuration Register 1 to set V
this bit to set V
current sources can continue to operate; however, the differ-
ence between V
current sources. (See
In Voltage Output mode when V
LM3554 operates in Pass Mode (see
At light loads the LM3554 switches over to a pulsed frequency
mode operation (light load comparator enabled). In this mode
the device will only switch as necessary to maintain V
within regulation. This mode provides a better efficiency due
to the reduction in switching losses which become a larger
portion of the total power loss at light loads.
OVER-VOLTAGE PROTECTION
The output voltage is limited to typically 5.6V (5.7V max). In
situations such as the current source open, the LM3554 will
raise the output voltage in order to try and keep the LED cur-
rent at its target value. When V
voltage comparator will trip and turn off both the internal NFET
and PFET. When V
will begin switching again.
CURRENT LIMIT
The LM3554 features 4 selectable current limits: 1A, 1.5A, 2A,
and 2.5A. These are selectable through the I
interface via bits 5 (CL0) and 6 (CL1) of the Flash Duration
Register. When the current limit is reached, the LM3554 stops
switching for the remainder of the switching cycle.
Since the current limit is sensed in the NMOS switch there is
no mechanism to limit the current when the device operates
in Pass Mode. In situations where there could potentially be
large load currents at OUT, and the LM3554 is operating in
Pass mode, the load current must be limited to 2.5A. In Boost
mode or Pass mode if V
the part stops switching, and the PFET operates as a current
source limiting the current to typically 350mA. This prevents
damage to the LM3554 and excessive current draw from the
battery during output short circuit conditions.
OUT
OUT
to 4.5V. In Voltage Output mode the LED
OUT
and V
MAXIMUM OUTPUT POWER
falls below 5.4V (typical), the LM3554
OUT
LOAD
LED
falls below approximately 2.3V,
= 0. Disabling light load can be
will be dropped across the
OUT
IN
is greater than V
OUT
reaches 5.6V the over-
PASS MODE
to 5V. Write a (0) to
2
C-compatible
section.)
section).
OUT
OUT
the