LM3559TLX National Semiconductor Corporation, LM3559TLX Datasheet - Page 13

• Manufacturer Part Number: LM3559TLX
• Description: Synchronous Boost Flash Driver With Dual 900 Ma High Side Current Sources 1.8a Total Flash Current
• Manufacturer: National Semiconductor Corporation

Overview
The LM3559 is a high-power white LED flash driver capable
of delivering up to 1.8A of LED current into a single LED, or
up to 900 mA into two parallel LEDs. The device incorporates
a 2MHz constant frequency, synchronous boost converter,
and two high side current sources to regulate the LED current
over the 2.5V to 5.5V input voltage range.
During operation when the output voltage is greater than V
– 150mV the boost converter switches and maintains at least
270 mV across both current sources (LED1 and LED2). This
minimum headroom voltage ensures that the current sinks
remain in regulation. When the input voltage rises above the
LED voltage + current source headroom voltage, the device
stops switching and turns the PFET on continuously (Pass
mode). In Pass mode the difference between (V
R
the current sources.
Four hardware control pins provide control of the LM3559.
These include a hardware Flash Enable (STROBE), Dual
Flash Interrupt inputs (TX1 and TX2) designed to interrupt the
flash pulse during high-battery current conditions, and a logic
high hardware enable (HWEN) that can be pulled low to rapid-
ly place the device into shutdown. Additional features of the
LM3559 include an internal 4-bit ADC for LED voltage moni-
toring, an internal comparator for LED thermal sensing via an
external NTC thermistor, a battery voltage monitor during
flash current turn-on which monitors VIN and optimizes the
flash current during low-battery voltage conditions, an input
voltage monitor that can force Torch mode or LED shutdown
of the Flash current during input under voltage conditions, a
low-power Indicator current source with programmable pat-
terns, and a mode for utilizing the flash LEDs as a privacy
indicator.
Control of the LM3559 is done via an I
face. This includes adjustment of the Flash and Torch current
levels, adjustment of the indicator LED currents and indicator
pattern, changing the Flash Timeout Duration, changing the
switch current limit, and reading back the ADC results. Addi-
tionally, there are 8 flag bits that indicate flash current timeout,
LED over-temperature, LED failure (by sensing LED short or
output OVP condition during Flash, Torch, or Privacy mode),
device thermal shutdown, V
ping of the VIN Flash Monitor, and the occurrence of a TX
interrupt (both TX1 and TX2).
STARTUP (ENABLING THE DEVICE)
Turn-on of the LM3559 is done through bits [1:0] of the Enable
Register. Bits [1:0] enable the device in Torch mode, Flash
mode, or Privacy Indicate mode. Additionally, bit 6 enables
the message indicator at the LEDI/NTC pin. On startup, when
V
as a current source and delivers 350 mA to the output capac-
itor. During this time both current sources (LED1, and LED2)
are off. When the voltage across the output capacitor reaches
2.2V the active current sources can turn on. At turn-on the
current sources step through each FLASH and TORCH level
until their target LED current is reached (32 µs/step). This
gives the device a controlled turn-on and limits inrush current
from the V
INDEPENDENT LED CONTROL
Bits [4:3] of the Enable register provide for independent turn-
on and turn-off of the LED1 or LED2 current sources. The LED
current is adjusted by writing to the Torch Brightness or Flash
Brightness Registers. Both the Torch Brightness and the
Flash Brightness Register provide for independent current
OUT
ON_P
is less than V
), and the voltage across the LEDs is dropped across
IN
supply.
IN
, the internal synchronous PFET turns on
IN
under-voltage condition, trip-
2
C-compatible inter-
IN
- I
LED
IN
x
13
programming for the LED currents in either LED1 or LED2.
(See
BRIGHTNESS REGISTER
PASS MODE
At turn-on when the output voltage charges up to (V
mV), the LM3559 will decide if the part operates in Pass Mode
or Boost mode. If the voltage difference between V
V
If the difference between V
mV, the device operates in Pass Mode. In Pass Mode the
boost converter stops switching, and the synchronous PFET
turns fully on bringing V
80 mΩ). In Pass Mode the inductor current is not limited by
the peak current limit. In this situation the output current must
be limited to 3A.
OVER-VOLTAGE PROTECTION
The output voltage is limited to typically 5V (5.075V max). In
situations such as the current source open, the LM3559 will
raise the output voltage in order to try to keep the LED current
at its target value. When V
comparator will trip and turn off both the internal NFET and
PFET switches. When V
LM3559 will begin switching again.
CURRENT LIMIT
The LM3559 features 4 selectable current limits: 1.4A, 2.1A,
2.7A, and 3.2A. These are programmable through the I
compatible interface via bits [6:5] of the Flash Duration Reg-
ister. When the current limit is reached, the LM3559 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 LM3559 is operating in
Pass mode, the load current must be limited to 3A. 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 350 mA. This prevents
damage to the LM3559, and excessive current draw from the
battery during output short-circuit conditions.
FLASH MODE
In Flash mode the LED current sources (LED1 and LED2)
each provide 16 different current levels from typically 56.25
mA (total) to 1.8A (total) in steps of 56.25 mA. The Flash cur-
rents are adjusted via the Flash Brightness Register. Flash
mode is activated by writing a (1, 1) to bits [1:0] of the Enable
Register or by enabling the hardware flash input (STROBE)
via bit [2] of Configuration Register 1 and then pulling the
STROBE pin high (high polarity). Once the Flash sequence
is activated both current sinks (LED1 and LED2) will ramp up
to their programmed Flash current level by stepping through
all Torch and Flash levels (32 µs/step) until the programmed
current is reached.
Bit [5] of the Enable Register (STROBE Level/Edge bit) de-
termines how the Flash pulse terminates. With the Level/
Edge bit = 1 the Flash current will only terminate when it
reaches the end of the Flash timeout period. With the Level/
Edge bit = 0, Flash mode can be terminated by pulling
STROBE low, programming bits [1:0] of the Enable Register
with (0,0), or by allowing the Flash timeout period to elapse.
If the Level/Edge bit = 0 and STROBE is toggled before the
end of the Flash timeout period the timeout period will reset.
Figure 1
the different Level/Edge bit settings.
LED
is less than 270 mV, the device operates in Boost Mode.
TORCH BRIGHTNESS REGISTER
and
Figure 2
detail the Flash pulse termination for
OUT
OUT
OUT
OUT
OUT
up to V
Descriptions.)
falls below 4.88V (typical), the
falls below approximately 2.3V
and V
reaches 5V the over-voltage
IN
LED
– I
IN
is greater than 270
x R
PMOS
and
www.national.com
(R
IN
OUT
FLASH
PMOS
– 150
and
2
C-
=