参数资料
型号: LTC1702IGN
厂商: Linear Technology
文件页数: 32/36页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM VM 24-SSOP
标准包装: 55
系列: PolyPhase®
PWM 型: 电压模式
输出数: 2
频率 - 最大: 750kHz
占空比: 93%
电源电压: 3 V ~ 7 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: 24-SSOP(0.154",3.90mm 宽)
包装: 管件
LTC1702
APPLICATIO N S I N FOR M ATIO N
FAULT BEHAVIOR
Changing the Output Voltage on the Fly
Some applications use a switching scheme attached to the
feedback resistors to allow the system to adjust the
LTC1702 output voltage. The voltage can be changed on
the fly if desired, but care must be taken to avoid tripping
the overvoltage fault circuit. Stepping the voltage upwards
abruptly is safe, but stepping down quickly by more than
15% can leave the system in a state where the output
voltage is still at the old higher level, but the feedback node
is set to expect a new, substantially lower voltage. If this
condition persists for more than 10 μ s, the overvoltage
fault circuitry will fire and latch off the LTC1702.
The simplest solution is to disable the fault circuit by
grounding the FAULT pin. Systems that must keep the
fault circuit active should ensure that the output voltage is
never programmed to step down by more than 15% in any
single step. The safest strategy is to step the output down
by 10% or less at a time and wait for the output to settle
to the new value before taking subsequent steps.
VID Applications
Certain microprocessors specify a set of codes that corre-
spond to power supply voltages required from the regula-
tor system. If these codes are changed on the fly, the same
caveats as above apply. In addition, the switching matrix
that programs the output voltage may vary its resistance
significantly over the entire span of output voltages,
potentially changing the loop compensation if the circuit is
not designed properly. With a typical type 3 feedback loop
(Figure 8), make sure that the R BIAS resistor is modified to
set the output voltage. The R1 resistor must stay constant
to ensure that the loop compensation is not affected.
TYPICAL APPLICATIO N S
3.3V IN , 2.5V/1.8V Output Power Supply
V IN
C4
D1, D2: MOTOROLA MBR0520LT1
D3: MOTOROLA MBRS320T3
C1: KEMET T510X477M006AS
C12, C20: PANASONIC EEFUE0G181R
D2
R1
10 μ F 10 ?
D1
+
C1
470 μ F
× 2
3.3V
± 5%
L1: SUMIDA CEP1254712-T007
L2: SUMIDA CDRH744734-JPS023
Q1A, Q1B, Q2A, Q2B: SILICONIX Si9804
Q3, Q4: 1/2 SILICONIX Si4966
C8
1 μ F
C6
1 μ F
C5
1 μ F
PV CC
I MAX2
R8
36k
C2
1 μ F
BOOST1
BOOST2
V OUT2
1.8V
L1
0.68 μ H
Q2B
Q2A
BG1
TG1
SW1
BG2
TG2
SW2
C3
1 μ F
Q3
L2
1 μ H
V OUT1
2.5V
12A
GND
C12 +
180 μ F
× 3
C15
1 μ F
V IN
10k
R3
4.3k
R4
10k
1%
R5
8.06k
1%
D3
Q1B
C11
820pF
Q1A
R2 39k
C7 1 μ F
LTC1702
I MAX1 PGND
PGOOD1 PGOOD2
FCB FAULT
RUN/SS RUN/SS2
COMP1 COMP2
SGND FB2
C16 1 μ F
Q4
C19
1000pF
R10
2.4k
R12
10.7k
1%
R13
4.99k
1%
+
C20
180 μ F
V IN
10k
5A
C21
1 μ F
GND
PGOOD1
R7 68k
FB1
V CC
R9 27k
PGOOD2
FAULT
C10
C9
C17
C18
100pF
20pF
100pF
1000pF
1702 TA02
1702fa
32
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