LM3553SD-HALF National Semiconductor, LM3553SD-HALF Datasheet - Page 10

• Manufacturer Part Number: LM3553SD-HALF
• Description: 1.2A Dual Flash LED Driver System with I2C Compatible
• Manufacturer: National Semiconductor

www.national.com
Register
General Purpose Register
Multi-Function Pin Control
Register
Current Step Time
Register
Torch Current Control
Register
Flash Current Control
Register
Flash Duration Control
Register
I
The chip address for LM3553 is 1010011, or 53hex.
INTERNAL REGISTERS OF LM3553
General Purpose Register
EN0-EN1: Set Flash LED mode
Indicator Mode sets I
and D2 is disabled.
VM: Enables Voltage Mode. Current sinks D1 and D2 are
turned off and the LM3553 will operate in a regulated voltage
boost mode. Setting the VM bit to a '1' does not override the
EN0 and EN1 bits stored in the general purpose register. The
default setting is '0'. If the LM3553 is in Voltage Mode and an
indicator, torch or flash command is issued, the LM3553 will
turn on the D1 and D2 current sources and begin regulating
the output voltage to a value equal to VFB (350mV or 450mV)
+ VLED.
2
C COMPATIBLE CHIP ADDRESS
VM
0
0
0
0
1
1
1
1
EN1
0
0
1
1
0
0
1
1
LED
= 20mA. In this mode, D1 is enabled
FIGURE 4.
FIGURE 5.
EN0
Internal Hex
0
1
0
1
0
1
0
1
Address
0xA0
0xB0
0xC0
0x10
0x20
0x50
Function
Shutdown
Indicator Mode
Torch Mode
Flash Mode
Voltage Mode
Indicator Mode
Torch Mode
Flash Mode
0001 1000
1110 0000
1111 1100
1000 0000
1000 0000
1111 0000
Power On
Value
20171410
20171405
10
VFB: Selects the regulation voltage for the LM3553. Setting
this VFB bit to a '0' sets the regulation voltage to 450mV while
setting the VFB bit to a '1' sets the regulation voltage to
350mV. Setting the VFB bit to a '1' during torch mode and/or
lower current flash modes (I
LED efficiency of the LM3553.
M/F Pin Control Register
RESET: Enables M/F as hardware RESET. '0' = Hardware
RESET, .'1' = GPIO or current sink depending on the MODE
bit. Default = '0'
MODE: Sets M/F mode. Default for M0DE = '0'. '0' = GPI,
and'1' = GPO
Note: When M/F is configured as an input, data is transfered from GPI to
DATA: GPIO Data. When the M/F is configured as an output
(GPO), DATA sets the GPO level. Example: DATA = '1', M/F
is set high or logic '1'. When the M/F pin is configured as an
input (GPI), DATA stores the GPI level. Example: M/F = '1',
DATA will be set to a '1'. Default for DATA = '0'.
OVP: Enables high-voltage OVP (OVP Bit ='1') or low-voltage
OVP (OVP Bit ='0'). Default = low-voltage mode '0'
OCL: SW Pin Current Limit Selector Bit: If OCL = '0', the in-
ductor current limit is 2.5A typ. If OCL = '1', the inductor
current limit is 1.7A typ.
Current Step Time Register
ST1-ST0: Sets current level stepping time for D1 and D2 dur-
ing the beginning and end of the flash or torch current wave-
form. '00' = 25µs, '01' = 50µs, '10' = 100µs, '11' = 200µs.
The current ramp-up/ramp-down times can be approximated
by the following equation:
T
equal to the decimal value of the brightness level (0
N
is enabled before going into a flash. If going straight into a
flash from an off-state, N
RAMPUP/RAMPDOWN
FLASH
DATA whenever an I
When configuring M/F as a GPO, the first write needs to take the
LM3553 out of RESET mode and a second write can then set the pin
to the GPO.
≤
127 and 0
M/F Functionality Configuration Table
RESET
0
1
1
= (N
≤
N
2
FLASH
START
C write command is issued to the LM3553.
FIGURE 6.
FIGURE 7.
START
MODE
X
0
1
LED
- N
≤
= 0
31). N
START
< 1A) will help improve the
M/F Function
START
+ 1) × t
RESET
GPO
GPI
= N
STEP
TORCH
where N is
20171409
20171418
if Torch
≤