LTC1436AIGN-PLL#TRPBF Linear Technology, LTC1436AIGN-PLL#TRPBF Datasheet - Page 18

• Manufacturer Part Number: LTC1436AIGN-PLL#TRPBF
• Description: IC SW REG SYNC STEP-DOWN 24-SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1436AIGN-PLL#TRPBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.19 ~ 9 V
• Current - Output: 50mA
• Frequency - Switching: 125kHz ~ 240kHz
• Voltage - Input: 3.5 ~ 30 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS
The output of the phase detector is a complementary pair
of current sources charging or discharging the external
filter network on the PLL LPF pin. The relationship
between the PLL LPF pin and operating frequency is
shown in Figure 7. A simplified block diagram is shown in
Figure 8.
If the external frequency (f
lator frequency (f), current is sourced continuously, pull-
ing up the PLL LPF pin. When the external frequency is less
than f
PLL LPF 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
LTC1436A
LTC1436-PLL-A/LTC1437A
18
PLLIN
FREQUENCY
50k
EXTERNAL
OSC
Figure 8. Phase-Locked Loop Block Diagram
, current is sunk continuously, pulling down the
1.3f
0.7f
Figure 7. Operating Frequency vs V
DETECTOR
FREQUENCY
f
PHASE
DETECTOR
O
O
O
DIGITAL
PHASE/
0
0.5
U
2.4V
1.0
INFORMATION
V
PLLLPF
U
PLLIN
(V)
1.5
) is greater than the oscil-
R
PLL LPF
LP
W
2.0
OSC
C
1436 F08
1436 F07
LP
PLLLPF
2.5
U
C
OSC
C
OSC
Low-Battery Comparator
The LTC1436A/LTC1437A have an on-chip low-battery
comparator which can be used to sense a low-battery
condition when implemented as shown in Figure 10. The
resistive divider R3, R4 sets the comparator trip point as
follows:
difference. 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
stable input to the voltage-controlled oscillator. The filter
components C
acquires lock. Typically, R
0.1µF. 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 9 will
provide a frequency shift from f
and V
on V
LP
V
LBTRIP
holds the voltage.
PLLLPF
PLLLPF
SGND
V
IN
.
=
Figure 9. Directly Driving PLL LPF Pin
increases from 0V to 2.4V. Do not exceed 2.4V
Figure 10. Low-Battery Comparator
PLL LPF
1 19 1
.
LP
R4
R3
V
and R
⎛
⎜
⎝
LBI
2.4V MAX
+
–
+
R
R
LP
1.19V REFERENCE
4
3
18k
LP
⎞
⎟
⎠
determine how fast the loop
LTC1436A
LTC1437A
= 10k and C
LP
O
and R
to 1.9f
3.3V OR 5V
LP
LBO
1436 F09
O
smooth out the
LP
as the voltage
1436 F10
is 0.01µF to
14367afb