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MAX8720

Dynamically Adjustable 6-Bit VID Step-Down Controller

Maxim Integrated 

Dynamically Adjustable 6-Bit VID

Step-Down Controller

PIN

28 QSOP

36 THIN

QFN

1

33

2

34

3

35

4

1

5

2

6

3

7, 8

4, 5

9

7

10

8

11

9

12

10

Pin Description

NAME

FUNCTION

V+

SHDN

TIME

FB

FBS

CC

S0, S1

VCC

TON

REF

ILIM

Battery Voltage-Sense Connection. Connect V+ to input power source. V+ is used only

for PWM one-shot timing. DH on-time is inversely proportional to input voltage over a 2V

to 28V range.

Shutdown Control Input. Connect SHDN to VCC for normal operation. Connect SHDN to

GND to put the controller into its shutdown state. Forcing SHDN to 12V to 15V disables

both the overvoltage-protection and undervoltage-protection circuits and clears the fault

latch. Do not connect SHDN to >15V.

Slew-Rate Adjustment Pin. Connect a resistor from TIME to GND to set the internal slew-

rate clock. A 470kΩ to 22kΩ resistor sets the clock from 38kHz to 818kHz, fSLEW =

150kHz x 120kΩ / RTIME. To reduce inrush current, fSLEW = 150kHz x 120kΩ / 4 x RTIME

during power-up and power-down transient.

Fast Feedback Input. Connect FB to the junction of the external inductor and output-

capacitor node (Figure 1).

Feedback Remote-Sense Input. For nonvoltage-positioned circuits, connect FBS to VOUT

directly at the load. FBS internally connects to the integrator that fine tunes the DC output

voltage. For voltage-positioned circuits, connect FBS directly to FB near the IC to disable the

FBS remote-sense integrator amplifier. To disable all three integrator amplifiers, connect FBS

to VCC.

Integrator Capacitor Connection. Connect a 47pF to 1000pF (47pF typ) capacitor from CC to

AGND to set the integration time constant. CC can be left open if FBS is connected to VCC.

Suspend-Mode Voltage-Select Input. S0 and S1 are four-level digital inputs that select the

suspend-mode VID code for the suspend-mode multiplexer inputs. If SUS is high, the

suspend-mode VID code is delivered to the DAC.

Analog Supply Input. Connect to the system supply voltage (+4.5V to +5.5V) through a series

10Ω resistor. Bypass VCC to analog ground with a 1µF or greater ceramic capacitor.

On-Time Selection Control Input. This is a four-level input that sets the K-factor to

determine DH on-time. Connect TON to the following pins for the indicated operation:

GND = 1000kHz

REF = 550kHz

Open = 300kHz

VCC = 200kHz

2.0V Reference Voltage Output. Bypass REF to analog ground with a 0.22µF or greater

ceramic capacitor. The reference can source up to 50µA for external loads. Loading REF

degrades output voltage accuracy according to the REF load regulation error.

Current-Limit Adjustment. The PGND–LX current-limit threshold defaults to 100mV if ILIM

is connected to VCC. In adjustable mode, the current-limit threshold voltage is 1/10th the

voltage seen at ILIM over a 0.5V to 3.0V range. The logic threshold for switchover to the

100mV default value is approximately VCC - 1V. Connect ILIM to REF for a fixed 200mV

threshold.

10 ______________________________________________________________________________________

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