LT3434
6
3434fb
UU
U
PI FU CTIO S
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
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.
When the PGFB pin rises above V
PGFB
, current is sourced
No Load 2A Step Response
Step Response
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Burst Mode Operation
Burst Mode Operation
V
OUT
50mV/DIV
I
OUT
500mA/DIV
V
IN
= 12V 5ms/DIV 3434 G14
V
OUT
= 3.3V
I
Q
= 100µA
V
OUT
50mV/DIV
I
OUT
500mA/DIV
V
IN
= 12V 5µs/DIV 3434 G15
V
OUT
= 3.3V
I
Q
= 100µA
V
OUT
50mV/DIV
I
OUT
1A/DIV
V
IN
= 12V 500µs/DIV 3434 G17
V
OUT
= 3.3V
C
OUT
= 100µF
V
OUT
50mV/DIV
I
OUT
1A/DIV
V
IN
= 12V 500µs/DIV 3434 G18
V
OUT
= 3.3V
C
OUT
= 100µF
I
LOAD(DC)
= 500mA
3.3V Dropout Operation
INPUT VOLTAGE (V)
0
OUTPUT VOLTAGE (V)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
4
3434 G24
123 53.50.5 1.5 2.5 4.5
V
OUT
= 3.3V
BOOST DIODE = DIODES INC B1100
LOAD CURRENT
0.25A
LOAD CURRENT
2.5A
INPUT VOLTAGE (V)
0
OUTPUT VOLTAGE (V)
4
5
6
35
3434 G25
3
2
12
46
1
0
V
OUT
= 5V
BOOST DIODE = DIODES INC B1100
LOAD CURRENT
0.25A
LOAD CURRENT
2.5A
5V Dropout Operation
