LT1977IFE#TR Linear Technology, LT1977IFE#TR Datasheet - Page 6

• Manufacturer Part Number: LT1977IFE#TR
• Description: IC REG SW 1.5A HV STPDWN 16TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT1977IFE#TR

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.2 ~ 54 V
• Current - Output: 1.5A
• Frequency - Switching: 500kHz
• Voltage - Input: 3.3 ~ 60 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

LT1977
TYPICAL PERFOR A CE CHARACTERISTICS
500mA/DIV
PI FU CTIO S
NC (Pins 1, 3, 5): No Connection.
SW (Pin 2): The SW pin is the emitter of the on-chip power
NPN switch. This pin is driven up to the input pin voltage
during switch on time. Inductor current drives the SW pin
negative during switch off time. Negative voltage is clamped
with the external catch diode. Maximum negative switch
voltage allowed is –0.8V.
V
switch. V
voltage on the BIAS pin is not present. High di/dt edges
occur on this pin during switch turn on and off. Keep the
path short from the V
capacitor, through the catch diode back to SW. All trace
inductance on this path will create a voltage spike at switch
off, adding to the V
6
20mV/DIV
IN
U
(Pin 4): This is the collector of the on-chip power NPN
V
OUT
I
SW
3.5
3.0
2.0
1.5
1.0
4.0
2.5
0.5
0
Burst Mode Operation
V
V
I
Dropout Operation
2
Q
IN
OUT
LOAD CURRENT = 250mA
V
BOOST DIODE = DIODES INC B1100
= 100µA
IN
OUT
= 12V
U
= 3.3V
powers the internal control circuitry when a
= 3.3V
2.5
INPUT VOLTAGE (V)
CE
2µs/DIV
U
3
LOAD CURRENT = 1.25A
voltage across the internal NPN.
IN
3.5
pin through the input bypass
W
4
U
1977 G15
1977 G23
4.5
500mA/DIV
50mV/DIV
V
I
OUT
OUT
6
5
4
3
2
0
1
V
V
C
I
Dropout Operation
No Load 1A Step Response
2
DC
IN
OUT
OUT
V
BOOST DIODE = DIODES INC B1100
LOAD CURRENT = 250mA
OUT
= 0mA
= 12V
2.5
= 3.3V
= 100µF
= 5V
3
INPUT VOLTAGE (V)
3.5
500µs/DIV
LOAD CURRENT = 1.25mA
4
BOOST (Pin 6): The BOOST pin is used to provide a drive
voltage, higher than the input voltage, to the internal
bipolar NPN power switch. Without this added voltage, the
typical switch voltage loss would be about 1.5V. The
additional BOOST voltage allows the switch to saturate
and its voltage loss approximates that of a 0.2Ω FET
structure.
C
of delay time between the PGFB pin exceeding its thresh-
old (V
When the PGFB pin rises above V
from the C
age on the external capacitor reaches an internal clamp
(V
resultant PG delay time is given by t = C
T
CT
4.5
(Pin 7): A capacitor on the C
), the PG pin becomes a high impedance node. The
PGFB
5
5.5
T
) and the PG pin set to a high impedance state.
pin into the external capacitor. When the volt-
1977 G17
6
1977 G24
6.5
500mA/DIV
500mA/DIV
20mV/DIV
50mV/DIV
V
V
I
OUT
OUT
OUT
I
SW
Burst Mode Operation
V
V
I
Step Response
V
V
C
I
DC
Q
IN
OUT
OUT
IN
OUT
= 100µA
= 350mA
= 12V
= 12V
T
= 3.3V
= 3.3V
= 100µF
pin determines the amount
PGFB
, current is sourced
500µs/DIV
5ms/DIV
CT
• V
CT
/I
CT
. If the
1977fa
1977 G14
1977 G18