LTC1434CGN#TRPBF Linear Technology, LTC1434CGN#TRPBF Datasheet - Page 12

• Manufacturer Part Number: LTC1434CGN#TRPBF
• Description: IC DC/DC CONV STEP-DOWN 20-SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1434CGN#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 3.3V, 5V, Adj
• Current - Output: 450mA
• Frequency - Switching: 125kHz ~ 240kHz
• Voltage - Input: 3 ~ 13.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 20-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS
LTC1433/LTC1434
If the external frequency (V
frequency f
the PLL LPF pin. When the external frequency is less than
f
pin. If the external and internal frequencies are the same
but exhibit a phase difference, the current sources turn on
for an amount of time corresponding to the phase differ-
ence. Thus the voltage on the PLL LPF pin is adjusted until
the phase and frequency of the external and internal
oscillators are identical. At this stable operating point the
phase comparator output is open and the filter capacitor
C
The loop filter components C
current pulses from the phase detector and provide a
12
PLLIN
0
LP
, current is sunk continuously, pulling down the PLL LPF
FREQUENCY
50k
EXTERNAL
holds the voltage.
Figure 9. Relationship Between Oscillator Frequency
and Voltage at PLL LPF Pin
Figure 10. Phase-Locked Loop Block Diagram
1.3f
0.7f
DETECTOR
f
0
FREQUENCY
O
O
O
PHASE
DETECTOR
, current is sourced continuously, pulling up
DIGITAL
0
PHASE/
0.5
U
2.4V
1.0
V
INFORMATION
PLLLPF
U
PLLIN
LP
(V)
1.5
) is greater than the center
and R
R
PLL LPF
LP
W
2.0
OSC
LP
1433/34 F09
1433/34 F10
C
LP
smooth out the
2.5
U
C
OSC
C
OSC
stable input to the voltage controlled oscillator. The filter
components C
acquires lock. Typically R
0.1 F. Be sure to connect the low side of the filter to SGND.
The PLL LPF pin can be driven with external logic to obtain
a 1:1.9 frequency shift. The circuit shown in Figure 11 will
provide a frequency shift from f
V
V
Low-Battery Comparator
The LTC1433/LTC1434 have an on-chip, low-battery com-
parator which can be used to sense a low-battery condi-
tion when implemented as shown in Figure 12. The resis-
tor divider R3/R4 sets the comparator trip point as follows:
The divided down voltage at the negative (–) input to the
comparator is compared to an internal 1.19V reference. A
40mV hysteresis is built in to assure rapid switching. The
output is an open-drain MOSFET and requires a pull-up
resistor to operate. This comparator is active in shutdown.
To save more shutdown quiescent current, this compara-
tor can be shut down by taking the LBI pin below 0.74V,
PLL LPF
PLL LPF
V
LBTRIP
.
increases from 0V to 2.4V. Do not exceed 2.4V on
V
IN
Figure 11. Directly Driving PLL LPF Pin
PLL LPF
Figure 12. Low-Battery Comparator
1 19
LP
R4
R3
.
and R
R
R
2.4V MAX
3
4
–
+
LP
LTC1433/LTC1434
1.19V REFERENCE
LP
18k
1
determine how fast the loop
= 10k and C
O
to 1.9f
3.3V OR 5V
1433/34 F11
O
LP
1433/34 F12
as the voltage
is 0.01 F to