Datasheet > IMP805LMJA

IMP805LMJA

更新时间： 2024-10-27 22:31:11

品牌	Logo	应用领域
IMP		电池微处理器监控
页数	文件大小	规格书
10页	227K
描述
レP POWER SUPPLY SUPERVISOR WITH BATTERY BACKUP SWITCH

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IMP805LMJA 数据手册

IMP690A, 692A, 802L, 802M, 805L

Application Information

Watchdog Input

Table 1. Pin Connections in Battery Backup Mode

As discussed in the Reset section, the Watchdog Input is used to

monitor microprocessor activity. It can be used to insure that the

microprocessor is in a continually responsive state by requiring

that the WDI pin be toggled every second. If the WDI pin is not

toggled within the 1.6 second window (minimum t_WD+ t_RS),

a reset pulse will be asserted to return the microprocessor to the

initial start-up state. Pulses as short as 50ns can be applied to the

WDI pin. If this feature is not used, the WDI pin should be open-

circuited or the logic placed into a high-impedance state to allow

the pin to float.

V_OUT

V_BATT

PFI

Connection

Connected to V_BATTthrough internal PMOS switch

Connected to V_OUT

Disabled

PFO

Logic-LOW

RESET Logic LOW (except on IMP805 where it is HIGH)

WDI Watchdog timer disabled

During the backup power mode, the internal circuitry of the

supervisory circuit draws power from the battery supply. While

_CCis still alive, the comparator circuits remain alive and the cur-

rent drawn by the device is typically 35µA. When V_CCdrops more

than 1.1V below V_BATT, the internal switchover comparator, the

PFI comparator and WDI comparator will shut off, reducing the

quiescent current drawn by the IC to less than 1µA.

Backup-Battery Switchover

A power loss can be made less severe if the system RAM contents

are preserved. This is achieved in the IMP690/692/802/805 by

switching from the failed V_CCto an alternate power source con-

nected at V_BATTwhen V is less than the reset threshold voltage

(V < V ), and V is less than V_BATT. The V_OUTpin is normally

connected to V through a 2Ω PMOS switch but a brown-out or

Backup Power Sources - Batteries

loss of V will cause a switchover to V_BATTby means of a 20Ω

Battery voltage selection is important to insure that the battery

does not discharge through the parasitic device diode D1 (see

PMOS switch. Although both conditions (V < V and V <

_BATT) must occur for the switchover to V_BATTto occur, V

will

OUT

Figure 4) when V_CCis less than V_BATTand V_CC> V .

be switched back to V_CCwhen V_CCexceeds V_RTirrespective of the

voltage at V_BATT. It should be noted that an internal device diode

Table 2. Maximum Battery Voltages

(D1 in Figure 4) will be forward biased if V_BATTexceeds V by

Part No.

IMP690A

IMP802L

IMP805L

IMP692A

IMP802M

MAXIMUM Battery Voltage

more than a diode drop when V_CCis switched to V_OUT. Because of

this it is recommended that V_BATTbe no greater than V_RT+0.6V.

4.80

4.55

V_BATT

V_CC

SW1

SW2

D1 D2

SW3

SW4

Although most batteries that meet the requirements of Table 2 are

acceptable, lithium batteries are very effective backup source due

to their high-energy density and very low self-discharge rates.

IMP690A IMP802L

IMP692A IMP802M

IMP805L

Battery Replacement while Powered

Batteries can be replaced even when the device is in a powered

state as long as V_CCremains above the reset threshold voltage V_RT.

In the IMP devices, a floating V_BATTpin will not cause a power-

supply switchover as can occur in some other supervisory

circuits. If V_BATTis not used, the pin should be grounded.

V_OUT

CONDITION

SW1/SW2 SW3/SW4

V_CC> Reset Threshold

Open

Closed

_CC< Reset Threshold and

V_CC> V_BATT

V_CC< Reset Threshold and

V_CC< V_BATT

Closed

Open

IMP690A/IMP802L/IMP805L Reset Threshold = 4.65V

IMP692A/IMP802M Reset Threshold = 4.4V

690A_06.eps

Figure 4. Internal device configuration of battery

switch-over function

1...3 4 567 8 9 10

中文翻译

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