Datasheet

LT1947
3
1947fa
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LT1947 is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V, V
SHDN
= 3.3V unless otherwise specified.
SYMBOL CONDITIONS MIN TYP MAX UNITS
Error Amplifier Voltage Gain EA1 and EA2 100 V/V
C
T
Current Source V
FB1
= 1.3V 4 5.5 6.5 µA
C
T
Threshold to Turn On Q3 1.25 1.28 1.30 V
FB1 Voltage to Begin C
T
Charge 1.17 1.2 1.23 V
SW1 Current Limit (Note 3) 1.1 1.4 2 A
SW2 Current Limit (Note 3) 0.35 0.6 1 A
SW1 Saturation Voltage I
SW1
= 800mA 0.230 0.280 V
SW2 Saturation Voltage I
SW2
= 300mA 0.3 0.36 V
SW1 Maximum Duty Cycle 82 %
SW2 Maximum Duty Cycle 85 %
Oscillator Frequency ● 2.3 3 3.5 MHz
V
ON
Switch Drop I
Q3
= 7mA 160 200 mV
SW1 Leakage Current Switch Off, SW1 = 3.3V 0.01 5 µA
SW2 Leakage Current Switch Off, SW2 = 3.3V 0.01 5 µA
SHDN Pin Bias Current V
SHDN
= 2.4V 10 25 µA
SHDN Pin High Active Mode 2.4 V
SHDN Pin Low Shutdown Mode 0.4 V
ELECTRICAL CHARACTERISTICS
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: Switch current limit guaranteed by design and/or correlation to
static tests.
3.3V TFT-LCD Converter Efficiency
AV
DD
LOAD CURRENT (mA)
0
35
EFFICIENCY (%)
40
50
55
60
85
70
50
100
125
1947 G01
45
75
80
65
25 75
150
175
200
V
IN
= 2.7V
V
IN
= 3.3V
V
IN
= 3V
Supply Current C
T
Current Source
–50 –25 0 25 50 75 100
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
12
10
8
6
4
1947 G02
SHDN = 2.4V
–50 –25 0 25 50 75 100
TEMPERATURE (°C)
C
T
CURRENT (µA)
–2
–4
–6
–8
–10
1947 G03
TYPICAL PERFOR A CE CHARACTERISTICS
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