Datasheet

3
LTC1772
1772fb
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Reference Voltage
vs Temperature
Normalized Frequency
vs Temperature
Undervoltage Lockout Trip
Voltage vs Temperature
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125 145
V
FB
VOLTAGE (mV)
1772 G01
825
820
815
810
805
800
795
790
785
780
775
V
IN
= 4.2V
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125 145
NORMALIZED FREQUENCY (%)
1772 G02
10
8
6
4
2
0
–2
–4
–6
–8
–10
V
IN
= 4.2V
DUTY CYCLE (%)
20
30 40 50 60 70 80 90 100
TRIP VOLTAGE (mV)
1772 G04
130
120
110
100
90
80
70
60
50
V
IN
= 4.2V
T
A
= 25°C
Maximum (V
IN
– SENSE
–
) Voltage
vs Duty Cycle
Shutdown Threshold
vs Temperature
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC1772E is guaranteed to meet specifications from 0°Cto
70°C. Specifications over the –40°C to 85°C operating temperature range
are assured by design, characterization and correlation with statistical
process controls. The LTC1772I is guaranteed to meet specified
performance from –40°C to 85°C. The LTC1772H is guaranteed to meet
specified performance from –40°C to 140°C.
Note 3: T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
T
J
= T
A
+ (P
D
• θ
JA
°C/W)
Operation at high junction temperatures degrades operating lifetimes.
Operating lifetimes at junction temperatures greater than 125°C is derated
to 1000 hours.
Note 4: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 5: The LTC1772 is tested in a feedback loop that servos V
FB
to the
output of the error amplifier.
Note 6: Peak current sense voltage is reduced dependent on duty cycle to
a percentage of value as given in Figure 2.
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125 145
TRIP VOLTAGE (V)
1772 G05
550
510
470
430
390
350
310
270
230
190
150
V
IN
= 4.2V
TEMPERATURE (°C)
–55 –35 –15 5 25 45 65 85 105 125 145
TRIP VOLTAGE (V)
1772 G03
2.14
2.10
2.06
2.02
1.98
1.94
1.90
1.86
1.82
1.78
1.74
V
IN
FALLING
ELECTRICAL CHARACTERISTICS