A4406 datasheet(15/27 Pages) ALLEGRO

No de pièce	A4406

Description	The A4406 is an automotive power management IC that uses a high frequency constant on-time 5.45 V pre-regulator to supply an internal 5 V linear regulator and a 3.3 V linear DMOS driver.

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Fabricant	ALLEGRO [Allegro MicroSystems]

Site Internet	http://www.allegromicro.com

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15 / 27 page

Constant On-Time Buck Regulator

With One External and One Internal Linear Regulator

A4406

15

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

oped across the external sense resistor, RCL, shown in the Typical

Application Circuit schematic. The 3.3V current limit can be

calculated using the following formula:

ICL = VCLV33 / RCL ,

(6)

where VCLV33 is as documented in the Electrical Characteris-

tics table, nominally 200 mV. Typically RCL will be a fairly low

value so it will not dissipate significant power, 1/4 W should be

adequate, but the tolerance should be 1% or less.

When ICL is exceeded, the maximum load current through the

external MOSFET is typically folded back to 48% of ICL as

shown in figure 7.

Charge Pump

The charge pump is used to generate a supply above VIN.

A 0.22 μF ceramic monolithic capacitor should be connected

between VCP and VIN to act as a reservoir to run the DMOS

switch. The VCP voltage is internally monitored to ensure that

the charge pump is disabled in the case of a fault condition.

A 0.22 μF ceramic monolithic capacitor should be connected

between CP1 and CP2.

ENBAT

This is a level-triggered enable input, use for enabling the device

based on a high voltage ignition or battery switch (via a 1 kΩ

resistor). The ENBAT comparator thresholds are VIGN(L) =

2.2 V(min)and VIGN(H) = 4.0 V (max). ENBAT is used only as a

momentary switch to enable or wake up the A4406. After ENBAT

is removed, ENB must be high to keep the A4406 enabled. The

ENB and ENBAT signals are logically ORed together internally

so either one may wake up the A4406 and both must be low to

disable the A4406. Only one of the two inputs must be pulled

high in order to enable the part. If there is no requirement for an

ignition switch, then ENBAT can be pulled low, which makes

ENB a single reset control.

If an external resistor and capacitor are used to form a low-pass

filter to the ENBAT pin, then a 100 Ω resistor must be used to

prevent the external capacitor from discharging into and damag-

ing the ENBAT pin. See the Typical Application Circuit sche-

matic for connection of these 3 components.

ENBATS

When a logic high is sensed on the ENBAT input, the ENBATS

output will go high, signaling to the user that the ignition input

is high. When a logic low is sensed on the ENBAT input, then

ENBATS will also transition to low. The ENBATS input logic

levels are identical to the ENBAT input logic levels.

ENB

This pin can be used as an enable input from either a DSP or from

a microcontroller. This input has an internal pull-down resistor so

it may be left unconnected if not used.

3.5

3.0

2.5

2.0

1.5

1.0

05

0

50

10

20

30

40

50

60

120

90

100 110

80

70

Percentage of Normal Current Se ng (%)

Figure 7. Foldback current limit of the V33 regulator

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