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LTC3619IDD#PBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P22
LTC3619
16
3619fa
3. The resistor divider, R1 and R2, must be connected
between the (+) plate of C
OUT1
and a ground sense
line terminated near GND (Pin 11). The feedback sig-
nals V
FB1
and V
FB2
should be routed away from noisy
components and traces, such as the SW lines (Pins 5
and 7), and their trace length should be minimized.
4. Keep sensitive components away from the SW pins, if
possible. The input capacitor C
IN
, C
LIM
and the resistors
R1, R2, R3 and R4, R
LIM
should be routed away from
the SW traces and the inductors.
applicaTions inForMaTion
5. A ground plane is preferred, but if not available, keep
the signal and power grounds segregated with small
signal components returning to the GND pin at a single
point. These ground traces should not share the high
current path of C
IN
or C
OUT
.
6. Flood all unused areas on all layers with copper.
Flooding with copper will reduce the temperature rise
of power components. These copper areas should be
connected to V
IN
or GND.
Figure 3a. LTC3619 Layout Diagram (See Board Layout Checklist)
V
IN
RUN2 RUN1
LTC3619
V
FB2
SW2
SW1
V
FB1
C
F2
C
F1
GNDRLIM
V
IN
2.5V TO 5.5V
V
OUT2
V
OUT1
3619 F03a
R3 R1
R4
L2 L1
R2
C
OUT2
C
IN
C
OUT1
BOLD LINES INDICATE HIGH CURRENT PATHS
PGOOD1PGOOD2
R
LIM
C
LIM
Figure 3b. LTC3619 Suggested Layout
V
IN
C
IN
V
OUT1
C
OUT1
C
OUT2
V
OUT2
R3 R1
R4 R2
C
F2
C
F1
GND
GND
GND VIA
V
IN
VIA
L1L2
3619 F03b
VIA TO V
OUT2
VIA TO V
OUT1
V
IN
SW2
PGOOD2
RUN2
V
FB2
SW1
PGD1
RLIM
RUN1
V
FB1
C
LIM
R
LIM
LTC3619
17
3619fa
applicaTions inForMaTion
Figure 4a. Design Example Circuit
V
IN
RUN2 RUN1
LTC3619
V
FB2
SW2
SW1
PGOOD1PGOOD2
V
FB1
C
F1
, 22pF
GNDRLIM
V
IN
USB INPUT 5V
V
OUT2
3.4V AT
800mA
V
OUT1
1.8V AT
400mA
3619 F04a
R4
276k
R2
118k
R3
59k
R1
59k
L2
1.5µH
L1
3.3µH
C
OUT2
2.2mF
×2
SuperCap
C
OUT1
10µF
C
IN
10µF
C
IN
, C
OUT1
: AVX 08056D106KAT2A
C
OUT2
: VISHAY 592D228X96R3X2T20H
L1: COILCRAFT LPS4012-332ML
L2: COILCRAFT LPS4012-152ML
R
LIM
116k
C
LIM
1000pF
+
Design Example
As a design example, consider using the LTC3619 in a
USB-GSM application, with V
IN
= 5V, I
INMAX
= 500mA, with
the output of channel 2 charging a SuperCap of 4.4mF.
The load on each channel requires a maximum of 400mA
and 800mA in active mode and 2mA in standby mode.
The output voltages are V
OUT1
= 1.8V and V
OUT2
= 3.4V.
Start with channel 1. First, calculate the inductor value
for about 40% ripple current (160mA in this example) at
maximum V
IN
. Using a derivation of Equation 1:
L1=
1.8V
2.25MHz • (160mA)
• 1−
1.8V
5V
= 3.2µH
For the inductor, use the closest standard value of 3.3µH.
A 10µF ceramic capacitor should be more than sufficient
for this output capacitor. As for the input capacitor, a
typical value of C
IN
= 10µF should suffice, if the source
impedance is very low.
The feedback resistors program the output voltage. To
maintain high efficiency at light loads, the current in these
resistors should be kept small. Choosing 10µA with the
0.6V feedback voltage makes R1~60k. A close standard
1% resistor is 59k. Using Equation 2.
R2=
V
OUT
0.6
−1
• R1=118k
An optional 22pF feedforward capacitor (C
F1
) may be used
to improve transient response.
Using the same analysis for channel 2 (V
OUT2
= 3.4V),
the results are:
L2 = 1.5µH
R3 = 59k
R4 = 276k
A feedforward capacitor is not used on channel 2 since
the 4.4mF SuperCap will inhibit any fast output voltage
transients.
Figure 4 shows the complete schematic for this example,
along with the efficiency curve and transient response.
Input current limit is set at 475mA average current, R
LIM
= 116k, C
LIM
= 1000pF. See Programming Input Current
Limit for selecting R
LIM
and Selection of C
LIM
Capacitance
for C
LIM
.
LTC3619
18
3619fa
applicaTions inForMaTion
Figure 4b. Efficiency and Power Loss vs Output Current
Figure 4c. Transient Response
OUTPUT CURRENT (A)
0.0001
0
EFFICIENCY (%)
POWER LOSS (W)
POWER LOSS (W)
10
20
30
40
80
70
60
50
90
100
0.0001
0.1
0.01
0.001
1
10
0.010.001
0.1
V
OUT
= 1.8V
1
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5V
OUTPUT CURRENT (A)
0.0001
0
EFFICIENCY (%)
10
20
30
40
80
70
60
50
90
100
0.0001
0.1
0.01
0.001
1
10
0.010.001
3619 F04b
0.1
V
OUT
= 3.4V
1
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 5V
20µs/DIV
V
OUT
100mV/DIV
AC-COUPLED
I
L
500mA/DIV
I
OUT
500mA/DIV
V
IN
= 5V, V
OUT
= 1.8V
I
LOAD
= 40mA TO 400mA
C
L
= 10µF
1ms/DIV
V
IN
1V/DIV
AC-COUPLED
I
IN
500mA/DIV
V
OUT
200mV/DIV
I
OUT
500mA/DIV
3619 F04c
V
IN
= 5V, 500mA COMPLIANT
R
LIM
= 116kΩ, C
LIM
= 1000pF
I
LOAD
= 0A TO 2A, C
OUT
= 4.4mF, V
OUT
= 3.4V
I
LIM
= 475mA, CHANNEL 1 NOT LOADED
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LTC3619IDD#PBF

Mfr. #:
Buy LTC3619IDD#PBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators 400mA/800mA Synchronous Step-Down DC/DC Converter with Average Input Current Limit
Lifecycle:
New from this manufacturer.
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