LM3560_14 Datasheet, PDF (40/48 Pages) Texas Instruments – Synchronous Boost Flash Driver

LM3560
SNOSB43B – SEPTEMBER 2011 – REVISED AUGUST 2013
I_PEAK =
I_LOAD
K
x
V_OUT
V_IN
+ 'I_L
where
'I_L =
V_IN x ⁽V_OUT - V_IN⁾
2 x f_SW x L x V_OUT
where ƒ_SW = 2MHz, and efficiency can be found in the Typical Performance Characteristics plots.
Manufacturer
TOKO
TOKO
TDK
TDK
L
2.2 µH
1 µH
1 µH
1 µH
Table 21. Recommended Inductors
Part Number
FDSD0312-H-2R02M
FDSD0312-H-1R0M
VLS252012T-1R0N
VLS4012ET-1R0N
Dimensions (L×W×H)
3 mm×3.2 mm×1.2 mm
3 mm×3.2 mm×1.2 mm
2 mm×2.5 mm×1.2 mm
4 mm x 4 mm x 1.2 mm
I_SAT
2.3A
3.4A
2.45A
2.8A
www.ti.com
(3)
R_DC
105 mΩ
43 mΩ
73 mΩ
50 mΩ
NTC THERMISTOR SELECTION
Programming bit [4] of Configuration Register 1 with a '1' selects NTC mode and makes the LEDI/NTC pin a
comparator input for flash LED thermal sensing. Figure 45 shows the LM3560 using the NTC thermistor circuit.
The thermal sensor resistor divider is composed of R3 and R(T), where R(T) is the Negative Temperature
Coefficient Thermistor, VBIAS is the bias voltage for the resistive divider, and R3 is used to linearize the NTC's
response around the NTC comparators trip point. C_BYP is used to filter noise at the NTC input.
1 2H/2.2 2H
10 2F
SW
IN
OUT
LM3560
LED1
HWEN
LED2
STROBE
TX1/TORCH
TX2
SDA
SCL
LEDI/NTC
GND
10 2F
VBIAS
R3
Flash
LED
Low Thermal
Impedance Between
R(T) and LED
R(T)
C_BYP
Figure 45. Typical Application Circuit with Thermistor
In designing the NTC circuit, we must choose values for VBIAS, R(T) and R3. To begin with, NTC thermistors
have a non-linear relationship between temperature and resistance:
R(T)
=
R_25°C
x
e
E_©§T
1
°C+
273
±
1_·
298_¹
(4)
where β is given in the thermistor datasheet and R_25C is the thermistor's value at +25°C. R3 is chosen so that the
temperature to resistance relationship becomes more linear and can be found by solving for R3 in the R(T) and
R3 resistive divider:
R3 = ^{( RT(TRIP) VBIAS - VTRIP)}
V_TRIP
(5)
where R(T)_TRIP is the thermistor's value at the temperature trip point and V_TRIP = 1V (typical). As an example,
with V_BIAS = 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:
40
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