LT3435
6
3435fa
OUTPUT VOLTAGE (V)
3435 G19
3.5
0
4.0
2.5
3.0
1.5
2.0
0.5
1.0
INPUT VOLTAGE (V)
2 2.5 3 3.5 4 4.5 5 5.5 6
LOAD CURRENT = 250mA
V
OUT
= 3.3V
BOOST DIODE = DIODES INC DFLS160
LOAD CURRENT = 2.5A
OUTPUT VOLTAGE (V)
3435 G20
5
0
6
3
4
1
2
INPUT VOLTAGE (V)
2 2.5 3 3.5 4 4.5 5 5.5 6.5 7 7.56
V
OUT
= 5V
BOOST DIODE = DIODES INC DFLS160
LOAD CURRENT = 2.5A
LOAD CURRENT = 250mA
No Load 2A Step Response Step Response
V
OUT
200mV/DIV
AC-COUPLED
I
OUT
1A/DIV
V
IN
= 12V 500µs/DIV 3435 G23
V
OUT
= 3.3V
C
OUT
= 100µF
V
OUT
200mV/DIV
AC-COUPLED
I
OUT
1A/DIV
V
IN
= 12V 500µs/DIV 3435 G24
V
OUT
= 3.3V
C
OUT
= 100µF
I
LOAD(DC)
= 500mA
NC (Pin 1): No Connection.
SW (Pins 2, 5): 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 nega-
tive switch voltage allowed is –0.8V.
V
IN
(Pins 3, 4): This is the collector of the on-chip power
NPN switch. V
IN
powers the internal control circuitry when
a 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
IN
pin through the input bypass
capacitor, through the catch diode back to SW. All trace
UU
U
PI FU CTIO S
TYPICAL PERFOR A CE CHARACTERISTICS
UW
inductance on this path will create a voltage spike at switch
off, adding to the V
CE
voltage across the internal NPN.
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 0.1Ω FET
structure.
C
T
(Pin 7): A capacitor on the C
T
pin determines the amount
of delay time between the PGFB pin exceeding its thresh-
old (V
PGFB
) and the PG pin set to a high impedance state.
Burst Mode Operation
Burst Mode Operation
V
OUT
50mV/DIV
AC-COUPLED
I
SW
500mA/DIV
V
IN
= 12V 10ms/DIV 3435 G21
V
OUT
= 3.3V
V
OUT
50mV/DIV
AC-COUPLED
I
SW
500mA/DIV
V
IN
= 12V 10µs/DIV 3435 G22
V
OUT
= 3.3V
Dropout Operation Dropout Operation
