参数资料
型号: LTC3823EGN
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: 4 A SWITCHING CONTROLLER, 200 kHz SWITCHING FREQ-MAX, PDSO28
封装: 0.150 INCH, PLASTIC, SSOP-28
文件页数: 9/24页
文件大小: 345K
代理商: LTC3823EGN
LTC3823
3823fb
mode, VOUT1mustbesethigherthanVOUT2.Toimplement
the ratiometric tracking, the ratio of the divider should be
exactly the same as the master IC’s feedback divider. Note
that the pin Z1/SSENABLE of the slave IC should be tied to
INTVCC so that the internal soft-start current is disabled
in both tracking modes or it will introduce a small error
on the tracking voltage depending on the absolute values
of the tracking resistive divider.
By selecting different resistors, the LTC3823 can achieve
different modes of tracking including the two in Figure 7.
So which mode should be programmed? While either
mode in Figure 7 satisfies most practical applications,
there do exist some tradeoffs. The ratiometric mode saves
a pair of resistors, but the coincident mode offers better
output regulation. This can be better understood with the
help of Figure 9. At the input stage of the slave IC’s error
amplifier, two common anode diodes are used to clamp
the equivalent reference voltage and an additional diode
is used to match the shifted common mode voltage. The
top two current sources are of the same amplitude. In the
coincident mode, the TRACK/SS voltage is substantially
higher than 0.6V at steady state and effectively turns off
D1. D2 and D3 will therefore conduct the same current
and offer tight matching between VFB2 and the internal
precision0.6Vreference.Intheratiometricmode,however,
TRACK/SS equals 0.6V at steady state. D1 will divert part
of the bias current to make VFB2 slightly lower than 0.6V.
Although this error is minimized by the exponential I-V
characteristic of the diode, it does impose a finite amount
of output voltage deviation. Furthermore, when the master
IC’s output experiences dynamic excursion (under load
transient, for example), the slave IC output will be affected
as well. For better output regulation, use the coincident
tracking mode instead of ratiometric.
applications information
TIME
(7a) Coincident Tracking
VOUT1
VOUT2
OUTPUT
VOLTAGE
TIME
3823 F07
(7b) Ratiometric Tracking
VOUT1
VOUT2
OUTPUT
VOLTAGE
Figure 7. Two Different Modes of Output Voltage Tracking
R3
R1
R4
R2
R3
VOUT2
R4
(8a) Coincident Tracking Setup
TO
VFB1
PIN
TO
TRACK/SS2
PIN
TO
VFB2
PIN
VOUT1
R1
R2
R3
VOUT2
R4
3823 F08
(8b) Ratiometric Tracking Setup
TO
VFB1
PIN
TO
TRACK/SS2
PIN
TO
VFB2
PIN
VOUT1
Figure 8. Setup for Coincident and Ratiometric Tracking
+
I
D1
TRACK/SS2
0.6V
VFB2
D2
D3
3823 F09
EA2
Figure 9. Equivalent Input Current of Error Amplifier
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