MAX8743(2004) 데이터 시트보기 (PDF) - Maxim Integrated

부품명

상세내역

일치하는 목록

MAX8743
(Rev.:2004)

Dual, High-Efficiency, Step-Down Controller with High Impedance in Shutdown

Maxim Integrated 

Dual, High-Efficiency, Step-Down

Controller with High Impedance in Shutdown

Table 3. Operating Mode Truth Table

ON1

GND

ON2

GND

SK IP

X

VCC GND VCC

DL1/DL2

Low/Low

Switching/Low

GND VCC VCC Low/Switching

VCC VCC VCC

Switching/

Switching

VCC GND GND Switching/Low

GND VCC GND Low/Switching

VCC VCC GND

Switching/

Switching

MODE

Shutdown

Run (PWM), Low Noise,

Side 1 Only

Run (PWM), Low Noise,

Side 2 Only

Run (PWM), Low Noise,

Both Sides Active

Run (PWM/PFM), Skip

Mode, Side 1 Only

Run (PWM/PFM), Skip

Mode, Side 2 Only

Run (PWM/PFM), Skip

Mode, Both Sides Active

VCC VCC

X

Low/Low

UV Fault (Either Side),

Thermal Fault, or

VCC Below UVLO

VCC VCC

X

High/High

OV Fault

(Either Side)

COMMENTS

Low-power shutdown state. ICC < 1µA (typ).

Low-noise, fixed-frequency PWM at all load conditions.

Low noise, high IQ.

Normal operation with automatic PWM/PFM switchover

for pulse skipping at light loads. Best light-load

efficiency.

Fault latch has been set by undervoltage protection

circuit, thermal shutdown, or VCC below UVLO. The

MAX8743 remains in fault mode until VCC power is

cycled below POR or ON1/ON2 is toggled.

Fault latch has been set by overvoltage protection circuit.

The MAX8743 remains in fault mode until VCC power is

cycled below the 2V (typ) POR level.

PWM is not allowed to initiate a new cycle (Figure 5). The

actual peak current is greater than the current-limit

threshold by an amount equal to the inductor ripple cur-

rent. Therefore, the exact current-limit characteristic and

maximum load capability are a function of the sense

resistance, inductor value, and battery voltage.

There is also a negative current limit that prevents

excessive reverse inductor currents when VOUT is

sinking current. The negative current-limit threshold is

set to approximately 120% of the positive current limit

and therefore tracks the positive current limit when

ILIM is adjusted.

The current-limit threshold is adjusted with an internal

5µA current source and an external resistor at ILIM. The

current-limit threshold adjustment range is from 25mV

to 250mV. In the adjustable mode, the current-limit

threshold voltage is precisely 1/10 the voltage seen at

ILIM. The threshold defaults to 50mV when ILIM is con-

nected to VCC. The logic threshold for switchover to the

50mV default value is approximately VCC - 1V.

Carefully observe the PC board layout guidelines to

ensure that noise and DC errors do not corrupt the cur-

rent-sense signal seen by CS_ and GND. Mount or

place the IC close to the low-side MOSFET and sense

resistor with short, direct traces, making a Kelvin sense

connection to the sense resistor. In Figure 1, the

Schottky diodes (D1 and D2) provide current paths

parallel to the Q2/RSENSE and Q4/RSENSE current

paths, respectively. Accurate current sensing requires

D1/D2 to be off while Q2/Q4 conducts. Avoid large cur-

rent-sense voltages that, combined with the voltage

across Q2/Q4, would allow D1/D2 to conduct. If very

large sense voltages are used, connect D1/D2 in paral-

lel with Q2/Q4 only.

MOSFET Gate Drivers (DH_, DL_)

The DH and DL drivers are optimized for driving mod-

erate-size, high-side and larger, low-side power

MOSFETs. This is consistent with the low duty factor

seen in the notebook CPU environment, where a large

VBATT - VOUT differential exists. An adaptive dead-time

circuit monitors the DL output and prevents the high-

side FET from turning on until DL is fully off. There must

be a low-resistance, low-inductance path from the DL

driver to the MOSFET gate for the adaptive dead-time

______________________________________________________________________________________ 15

Share Link: