MC13181 View Datasheet(PDF) - Motorola => Freescale

Part Name

Description

Manufacturer

MC13181

Wireless Power Management Integrated Circuit

Motorola => Freescale 

Circuit Features

3.2 Reference Regulator

The Reference Regulator supplies a precise 1.265 V for use by the other on-chip regulators. To maintain

spectral purity on the LDO regulators, this internal reference is not intended for external loading. A pin is

provided for an off-chip 0.47 µF capacitor for bypassing.

The reference regulator derives its power from the VCC1 pin. Since the reference regulator supplies

reference to the other regulators, power should not be applied to VCC2 if VCC1 is unpowered.

3.3 Shutdown

The active-low shutdown input disables all regulators and logic. In the shutdown state, the total IC current

consumption is 2.0 µA. Shutdown also disconnects the input resistor of the divider on the VIN- input to the

comparator. As this would typically be connected to VCC for battery voltage detection. Shutting down

MC13181 removes this approximately 5.0 µA current.

Care should be taken if this pin is to be driven from a processor operating on a voltage supplied by

MC13181.

3.4 Reset Circuit

The RESET_B output goes high after a delay, based on the delay capacitor. It is initiated when VLDO_1.85

rises above the reset threshold of 1.70 V. When VLDO_1.85 falls below the reset threshold, RESET_B goes

low with no delay.

To calculate the value of the delay capacitor needed for a given delay, the formula C/I = dV/dT can be

used. At the start of the delay, the capacitor is shorted nearly to 0 V, and then charged with a 500 nA

current source until its voltage reaches the reference voltage, 1.265 V.

T delay = C * V / I, simplifies to

T delay (ms) ~= 2.53 x C (nF)

or,

C (nF) ~= T / 2.53 (T in ms)

Note: The threshold voltage, resistance of the shorting FET and the current source will vary with

temperature and VCC2, so the resulting delay will vary by 2:1 or more.

3.5 Comparator with Programmable Hysteresis

The MC13181 includes a general purpose comparator. The IC's VIN- input incorporates internal resistors

scaling (by a factor of approximately 0.44) the voltage to the minus input of the comparator. The IC's

VIN+ input is directly connected to the plus input of the comparator. A typical application connects the

VIN- input to VCC2 and VIN+ to the reference output for Under-Voltage Detection. The scaling resistors

thereby set the threshold to 2.88 V with no additional components required.

Hysteresis, of typically 30 mV, can be enabled or disabled via the HYSSEL pin (low is enable), allowing

versatility for general purpose applications.

The comparator may be used for general purpose applications, if the fixed divider ratio is accounted for.

The inputs should not go lower than 1.0 V. The plus input should not exceed VCC2 - 1.0 V and the minus

input should not exceed VCC2.

The output of the comparator is push-pull, referenced to VLDO_1.85.

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MC13181 Advance Information

MOTOROLA

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