Rainbow-electronics MAX1844 Manual do Utilizador descarregar pdf (Página 5)

MAX1844

High-Speed Step-Down Controller with

Accurate Current Limit for Notebook Computers

_______________________________________________________________________________________ 5

PARAMETER CONDITIONS

MIN TYP MAX

UNITS

Minimum Off-Time (Note 2) 500 ns

Quiescent Supply Current (V

)

FB forced above the regulation point 800 µA

Quiescent Supply Current (V

)

FB forced above the regulation point 5 µA

Quiescent Supply Current (V+) Measured at V+ 40 µA

Shutdown Supply Current (V

) SHDN = GND 5 µA

Shutdown Supply Current (V

) SHDN = GND 5 µA

Shutdown Supply Current (V+) SHDN = GND, V+ = 28V, V

= V

= 0 or 5V 5 µA

Reference Voltage V

= 4.5V to 5.5V, no external REF load

1.98

2.02

Overvoltage Trip Threshold

(Fixed-Threshold Mode)

With respect to error comparator threshold, no load

OVP = GND, rising edge, hysteresis = 1%

12 17 %

External feedback, measured at FB with respect to

OVP

1V < V

OVP

1.8V, rising edge, hysteresis = 1%

-30

+30

Overvoltage Comparator Offset

(Adjustable-Threshold Mode)

Internal feedback, measured at OUT with respect to the

nominal OUT regulation voltage, 1V < V

OVP

< 1.8V

-3.5

+3.5

PGOOD Trip Threshold (Lower)

With respect to error comparator threshold, no load

OUT falling edge, hysteresis = 1%

-12.5

-7.5

PGOOD Trip Threshold (Upper)

With respect to error comparator threshold, no load

OUT rising edge, hysteresis = 1%

7.5

12.5

PGOOD Output Low Voltage I

SINK

= 1mA 0.4 V

PGOOD Leakage Current High state, forced to 5.5V 1 µA

Current-Limit Threshold (Fixed) GND - V

, ILIM = V

85 115 mV

GND - V

, V

ILIM

= 0.5V 35 65

Current-Limit Threshold

(Adjustable)

GND - V

, V

ILIM

= 2V 160 240

Undervoltage

Lockout Threshold

Rising edge, hysteresis = 20mV,

PWM disabled below this level

4.1 4.4 V

Logic Input High Voltage LATCH, SHDN, SKIP 2.4 V

Logic Input Low Voltage LATCH, SHDN, SKIP 0.8 V

Logic Input Current LATCH, SHDN, SKIP -1 1 µA

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, V+ = 15V, V

= V

= 5V, SKIP = GND, T

= -40°C to +85°C, unless otherwise noted.) (Note 3)

Note 1: When the inductor is in continuous conduction, the output voltage will have a DC regulation level higher than the error com-

parator threshold by 50% of the ripple. In discontinuous conduction (SKIP = GND, light load), the output voltage will have a

DC regulation level higher than the trip level by approximately 1.5% due to slope compensation.

Note 2: On-time and off-time specifications are measured from 50% point to 50% point at the DH pin with LX = GND, V

BST

= 5V,

and a 250pF capacitor connected from DH to LX. Actual in-circuit times may differ due to MOSFET switching speeds.

Note 3: Specifications to -40°C are guaranteed by design, not production tested.

Note 4: Production testing limitations due to package handling require relaxed maximum on-resistance specifications for the QFN

package. The MAX1844EEP and MAX1844EGP contain the same die and the QFN package imposes no additional resis-

tance in-circuit.

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