LM3559TLX/NOPB National Semiconductor, LM3559TLX/NOPB Datasheet - Page 37

• Manufacturer Part Number: LM3559TLX/NOPB
• Description: LM3559
• Manufacturer: National Semiconductor
• Series: -r

Specifications of LM3559TLX/NOPB

• Constant Current: Yes
• Constant Voltage: -
• Topology: High Side, PWM, Step-Up (Boost)
• Number Of Outputs: 2
• Internal Driver: Yes
• Type - Primary: Flash/Torch
• Type - Secondary: White LED
• Frequency: 1.8MHz ~ 2.2MHz
• Voltage - Supply: 2.5 V ~ 5.5 V
• Voltage - Output: -
• Mounting Type: Surface Mount
• Package / Case: 16-UFBGA
• Operating Temperature: -40°C ~ 85°C
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

NTC THERMISTOR SELECTION
Programming bit [4] of Configuration Register 1 with a (1) se-
lects NTC mode and makes the LEDI/NTC pin a comparator
input for flash LED thermal sensing.
LM3559 using the NTC thermistor circuit. The thermal sensor
resistor divider is composed of R3 and R(T), where R(T) is
In designing the NTC circuit, we must choose values for
V
non-linear relationship between temperature and resistance:
where β is given in the thermistor datasheet and R
thermistors value at +25°C. R3 is chosen so that the temper-
ature-to-resistance relationship becomes more linear and can
be found by solving for R3 in the R(T) and R3 resistive divider:
BIAS
Manufacturer
, R(T) and R3. To begin with, NTC thermistors have a
TDK
TDK
2.2 µH
1µH
L
FIGURE 19. LM3559 Typical Application Circuit with Thermistor
Figure 19
VLS252012T-2R2M1R3
VLS4012ET-1R0N
Part Number
shows the
25C
is the
37
the Negative Temperature Coefficient Thermistor, V
bias voltage for the resistive divider, and R3 is used to lin-
earize the NTC's response around the NTC comparators trip
point. C
where R(T)
point and V
2.5V and a thermistor whose nominal value at +25°C is 100
kΩ and a β = 4500K, the trip point is chosen to be +93°C. The
value of R(T) at 93°C is:
Figure 20
of the previous example.
Dimensions (L×W×H)
4mm x 4mm x 1.2mm
2mm×2.5mm×1.2mm
BYP
shows the linearity of the thermistor resistive divider
TRIP
is used to filter noise at the NTC input.
TRIP
is the thermistors value at the temperature trip
= 1V (typical). As an example, with V
30102830
2.8A
1.5A
I
SAT
www.national.com
50mΩ
TBD
R
BIAS
DC
BIAS
is the
=