参数资料
型号: LTC3850IGN-2#TRPBF
厂商: Linear Technology
文件页数: 25/36页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM CM 28-SSOP
产品培训模块: LTC3850 Dual Output DC/DC Switching Regulator Controller
标准包装: 2,500
系列: PolyPhase®
PWM 型: 电流模式
输出数: 2
频率 - 最大: 860kHz
占空比: 97.2%
电源电压: 4 V ~ 30 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 85°C
封装/外壳: 28-SSOP(0.154",3.90mm 宽)
包装: 带卷 (TR)
LTC3850-2
APPLICATIONS INFORMATION
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the IC. These items are also illustrated graphically in the
layout diagram of Figure 12. Figure 13 illustrates the current
waveforms present in the various branches of the 2-phase
synchronous regulators operating in the continuous mode.
Check the following in your layout:
1. Are the top N-channel MOSFETs M1 and M3 located within
1 cm of each other with a common drain connection at
C IN ? Do not attempt to split the input decoupling for the
two channels as it can cause a large resonant loop.
2. Are the signal and power grounds kept separate? The
combined IC signal ground pin and the ground return
of C INTVCC must return to the combined C OUT (–)
terminals. The V FB and I TH traces should be as short
as possible. The path formed by the top N-channel
MOSFET, Schottky diode and the C IN capacitor should
have short leads and PC trace lengths. The output
capacitor (–) terminals should be connected as close
as possible to the (–) terminals of the input capacitor
by placing the capacitors next to each other and away
from the Schottky loop described above.
3. Do the LTC3850-2 V FB pins’ resistive dividers connect to
the (+) terminals of C OUT ? The resistive divider must be
connected between the (+) terminal of C OUT and signal
ground. The feedback resistor connections should not
be along the high current input feeds from the input
capacitor(s).
4. Are the SENSE + and SENSE – leads routed together with
minimum PC trace spacing? The ?lter capacitor between
SENSE + and SENSE – should be as close as possible
to the IC. Ensure accurate current sensing with Kelvin
connections at the sense resistor or inductor, whichever
5. Is the INTV CC decoupling capacitor connected close to
the IC, between the INTV CC and the power ground pins?
This capacitor carries the MOSFET drivers current peaks.
An additional 1μF ceramic capacitor placed immediately
next to the INTV CC and PGND pins can help improve
noise performance substantially.
6. Keep the switching nodes (SW1, SW2), top gate nodes
(TG1, TG2), and boost nodes (BOOST1, BOOST2) away
from sensitive small-signal nodes, especially from the
opposite channel’s voltage and current sensing feedback
pins. All of these nodes have very large and fast moving
signals and therefore should be kept on the “output
side” of the LTC3850-2 and occupy minimum PC trace
area. If DCR sensing is used, place the top resistor
(Figure 2b, R1) close to the switching node.
7. Use a modi?ed “star ground” technique: a low imped-
ance, large copper area central grounding point on
the same side of the PC board as the input and output
capacitors with tie-ins for the bottom of the INTV CC
decoupling capacitor, the bottom of the voltage feedback
resistive divider and the SGND pin of the IC.
PC Board Layout Debugging
Start with one controller at a time. It is helpful to use a
DC-50MHz current probe to monitor the current in the
inductor while testing the circuit. Monitor the output
switching node (SW pin) to synchronize the oscilloscope
to the internal oscillator and probe the actual output voltage
as well. Check for proper performance over the operating
voltage and current range expected in the application. The
frequency of operation should be maintained over the input
voltage range down to dropout and until the output load
drops below the low current operation threshold—typically
10% of the maximum designed current level in Burst
Mode operation.
is used for current sensing.
38502f
25
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