High-Speed Step-Down Controller with

Accurate Current Limit for Notebook Computers

8

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PIN

QSOP

QFN

NAME

FUNCTION

1

18

CS

Current-Sense Input. Connect a low-value current-sense resistor between CS and GND for accurate

current sensing. For lower power dissipation (less accurate) current sensing, connect CS to LX to

use the synchronous rectifier as the sense resistor. The PWM controller will not begin a cycle unless

the current sensed at CS is less than the current-limit threshold programmed at ILIM.

2

19

LATCH

Overvoltage Protection Latch Control Input. The synchronous rectifier MOSFET is always forced to

the on state when an overvoltage fault is detected. If LATCH is low, the synchronous rectifier remains

normal operation resumes when the overvoltage condition ends.

3

20

SHDN

Shutdown Control Input. Drive SHDN to GND to force the MAX1844 into shutdown. Drive or connect

protection fault latches.

4

1

OVP

Overvoltage Protection Control Input. An overvoltage fault occurs if the internal or external feedback

voltage exceeds the voltage at OVP. Apply a voltage between 1V and 1.8V to set the overvoltage

limit between 100% and 180% of nominal output voltage. Connect to GND to assert the default

detection and clear the overvoltage protection fault latch.

5

2

FB

adjustable output (1V to 5.5V), connect FB to a resistive-divider from the output voltage. The FB

regulation level is 1V.

6

3

OUT

Output Voltage Sense Connection. Connect directly to the junction of the external output filter

capacitors. OUT senses the output voltage to determine the on-time for the high-side switching

MOSFET. OUT also serves as the feedback input in fixed-output modes.

7

4

ILIM

Current-Limit Threshold Adjustment. The current-limit threshold at CS is 0.1 times the voltage at ILIM.

Connect ILIM to a resistive-divider (typically from REF) to set the current-limit threshold between

threshold.

8

5

REF

2V Reference Voltage Output. Bypass to GND with a 0.22µF (min) bypass capacitor. Can supply

50µA for external loads. Reference turns off in shutdown.

9

6

UVP

Undervoltage Protection Control Input. An undervoltage fault occurs if the internal or external

feedback voltage is less than the voltage at UVP. Apply a voltage between 0.4V and 1V to set the

the default undervoltage limit of 70% of the nominal output voltage. Connect to GND to disable

undervoltage fault detection and clear the undervoltage protection latch.

10

7

PGOOD

Power-Good Open-Drain Output. PGOOD is low when the output voltage is more than 10% above or

below the normal regulation point or during soft-start. PGOOD is high impedance when the output is

in regulation and the soft-start circuit has terminated. PGOOD is low in shutdown.

11

8

GND

Analog and Power Ground

12

9

DL

13

10

Supply Input for the DL Gate Drive. Connect to the system supply voltage, 4.5V to 5.5V. Bypass to

GND with a 1µF (min) ceramic capacitor.

Pin Description