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參數(shù)資料
| 型號： | LM3655TLX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 電源管理 |
| 英文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, BGA25 |
| 封裝： | 2.5 X 2.5 MM, MICRO SMD, 25 PIN |
| 文件頁數(shù)： | 6/21頁 |
| 文件大?。?/td> | 833K |
| 代理商： | LM3655TLX |
13.0 Safety Functions (Continued)
it operates in linear mode. Q1 typically has an input voltage rating of 30V (see Section 14.1 CHARGE PASS TRANSISTOR (Q1)).
However, if Q1 fails as a short, the shunt control mechanism of the IC will still protect the phone and cell from high voltages. The
internal M3 shunt transistor is used to clamp the VIN, CELL and RADIO_B+ power pins to safe values.
13.1.2 Safety Shunt/Crowbar Operation
The LM3655 only activates the over-voltage protection if there is an internal failure of the LM3655 or a failure to the external
components, such as Q1 being shorted. Should one of these failures occur and the cell voltage exceeds a nominal level of 4.35V
(V
SHUNT), M3 will operate as a shunt regulator limiting the voltage at the cell terminal to VSHUNT. A secondary shunt activation
mechanism occurs if V
IN exceeds a nominal level of 5.2V(VSHUNT_INPUT).
When operating as a shunt regulator (in the linear mode of M3), excessive current may cause M3 power dissipation to exceed
safe limits if uncontrolled. If the M3 current limit of 4 Amps (typical I
FAST_CB) is exceeded, the IC will protect itself by turning M3
fully on in order to shunt the current. When in the safety shunt crowbar mode, the IC will turn off Q1 to stop the charge current
assuming that the external components and the control circuit of the IC are still operational.
13.1.3 Standby Shunt Mode
Another protection feature of the IC is a Standby shunt mode. When there is no charger present M3 is turned on as it would be
in Crowbar mode. Q1 is already turned off because the charger isn’t present. M3 is turned off when there becomes a charger
present. In this condition, the other crowbar modes function as is. Standby shunt mode doesn’t interfere with the fast and thermal
(see Section 13.1.4 Thermal Crowbar Mode and Section 13.1.5 Fast Shunt Operation) crowbar modes.
13.1.4 Thermal Crowbar Mode
Another safety protection feature of the IC is the thermal crowbar protection. As the charge power supply’s current compliance
increases, significant power dissipation occurs and the junction temperature of the IC could approach T
CB. This is the ‘Crowbar1’
initiation temperature and the power NMOS device M3 will be switched to full conduction mode in order to protect the IC. The
PMOS device M5 is switched off in Crowbar mode to prevent high cell discharge currents. The charge power supply’s current may
or may not open the external discrete fuse. If the fuse survives, the only recovery method from Crowbar1 mode is for the junction
temperature to reduce below T
RESET while in this mode for at least
τ
crowbar1. When in the thermal crowbar mode, the IC will turn
off Q1 to stop the charge current assuming that the external components and the control circuit of the IC are still operational.
13.1.5 Fast Shunt Operation
The VIN pin voltage is also AC-coupled to the shunt control network to provide a “fast comparator” function that can activate the
shunt transistor quickly in response to a fast-rising transient on the input. This allows the shunt device to be activated prior to the
other means of activation such as exceeding I
FAST_CB or thermal crowbar mode and bypasses the delays associated with the
DC-level sensitive comparator circuits.
In actual operation it will typically be very unlikely to activate the input shunt without activating the cell-initiated shunt mechanism
because the two voltages are related via M5 conduction.
13.1.6 Shunt Circuit Parametric Specifications
Unless otherwise noted, the following shunt specifications apply over the Normal Temperature Range.
Specification
Test Conditions
Min
Typ
Max
Units
Crowbar Temperature “T
CB”ISHUNT = 1A
105
120
135
C
Crowbar Reset Temperature “T
RESET”ISHUNT = 0A
607590
C
Fast Crowbar Current “I
FAST_CB”
τ
FAST_CB = minimum
2
4
7.5
A
Fast Crowbar Delay “
τ
FAST_CB”ISHUNT = 10A
1
50
s
Crowbar1 Sustain Time “
τ
CROWBAR1”ISHUNT =1A
4
8
16
s
Crowbar2 Sustain Time “
τ
CROWBAR2”ISHUNT = 10A
32
64
128
ms
Primary Shunt Control Voltage “V
SHUNT”at
(CELL) Pin @ 25C
@ Normal Termperature Range
I
VIN = 50 mA, IDETECT = 200 A
4.30
4.25
4.35
4.40
4.45
V
SHUNT_CELL –VTERMH
100
190
350
mV
Secondary Shunt Control Voltage at V
IN Pin
(V
SHUNT_INPUT)
I
VIN =50mA,
V
DETECT =0
4.7
5.2
5.7
V
τ
STBYSHUNT
Delay when CP goes from 1 to 0 before M3
gets turned on.
125
ms
V
STBY_SHUNT
0.1A to 2A into V
IN
0.5
1.1
2.2
V
LM3655
www.national.com
14
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