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1646I 参数 Datasheet PDF下载

1646I图片预览
型号: 1646I
PDF下载: 下载PDF文件 查看货源
内容描述: CompactPCI的双通道热插拔控制器 [CompactPCI Dual Hot Swap Controller]
分类和应用: 控制器PC
文件页数/大小: 20 页 / 400 K
品牌: Linear [ Linear ]
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LTC1646  
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W U U  
APPLICATIO S I FOR ATIO  
4. Programmable foldback current limit: a programmable  
analog current limit with a value that depends on the  
output voltage. If the output is shorted to ground, the  
current limit drops to keep power dissipation and  
supply glitches to a minimum.  
The main 3.3V and 5V inputs to the LTC1646 come from  
the medium length power pins. The long 3.3V, 5V connec-  
tor pins are shorted to the medium length 5V and 3.3V  
connector pins on the CPCI plug-in card and provide early  
power for the LTC1646’s precharge circuitry, the V(I/O)  
pull-up resistors and the PCI bridge chip. The BD_SEL#  
signal is connected to the OFF/ON pin while the PWRGD  
pin is connected to the HEALTHY# signal. The HEALTHY#  
signal is combined with the PCI_RST# signal on-chip to  
generate the LOCAL_PCI_RST# signal which is available  
at the RESETOUT pin.  
5. Dual-level,programmable5Vand3.3Vcircuitbreakers:  
this feature is enabled when the TIMER pin voltage  
exceeds 1.25V. If either supply exceeds current limit  
for more than 21µs, the circuit breaker will trip, the  
supplies will be turned off, and the FAULT pin is pulled  
low. In the event that either supply exceeds three times  
the set current limit, all supplies will be turned off and  
the FAULT pin is pin is pulled low without delay.  
The power supplies are controlled by placing external  
N-channel pass transistors in the 3.3V and 5V power  
paths.  
6. 15V high side drive for external 3.3V and 5V N-channel  
MOSFETs.  
Resistors R1 and R2 provide current fault detection and  
R5 and C1 provide current control loop compensation.  
Resistors R3 and R4 prevent high frequency oscillations  
in Q1 and Q2.  
7. PWRGD output: monitors the voltage status of the  
supply voltages.  
8. PCI_RST# combined on-chip with HEALTHY# to create  
LOCAL_PCI_RST# output. If HEALTHY# deasserts,  
LOCAL_PCI_RST# is asserted independent of  
PCI_RST#.  
When the CPCI card is inserted, the long 5V and 3.3V  
connector pins and GND pins make contact first. The  
LTC1646’s precharge circuit biases the bus I/O pins to 1V  
during this stage of the insertion (Figure 2). The 5V and  
3.3V medium length pins make contact during the next  
stage of insertion, but the slot power is disabled as long  
as the OFF/ON pin is pulled high by the 1.2k pull-up  
resistortoV(I/O). Duringthefinalstageofboardinsertion,  
the BD_SEL# short connector pin makes contact and the  
OFF/ON pin can be pulled low. This enables the pass  
transistors to turn on and a 5µA current source is con-  
nected to the TIMER pin.  
9. Precharge output: on-chip reference and amplifier pro-  
vide 1V for biasing bus I/O connector pins during CPCI  
card insertion and extraction.  
10. Space saving 16-pin SSOP package.  
PCI Power Requirements  
CPCIsystemsmayrequireuptofourpowerrails:5V,3.3V,  
12V and –12V. The LTC1646 is designed for CPCI applica-  
tions which only use the 5V and/or 3.3V supplies. The  
tolerance of the supplies as measured at the components  
on the plug-in card is summarized in Table 1.  
The current in each pass transistor increases until it  
reaches the current limit for each supply. The 5V and 3.3V  
supplies are then allowed to power up based on one of the  
following power-up rates:  
Table 1. PCI Power Supply Requirements  
SUPPLY  
5V  
TOLERANCE  
5V ±5%  
CAPACITIVE LOAD  
<3000µF  
ILIMIT(5V)  
ILIMIT(3V)  
dV 13µA  
=
,or =  
,or =  
(1)  
dt  
C1  
CLOAD(5VOUT)  
CLOAD(3VOUT)  
3.3V  
3.3V ±0.3V  
<3000µF  
whichever is slower.  
Current limit faults are ignored while the TIMER pin  
voltage is ramping up and is less than 1.25V. Once both  
supply voltages are within tolerance, HEALTHY# will pull  
Power-Up Sequence  
The LTC1646 is specifically designed for hot swapping  
CPCI boards. The typical application is shown in Figure 1.  
low and LOCAL_PCI_RST# is free to follow PCI_RST#.  
1646fa  
10