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MAX8792

Single Quick-PWM Step-Down Controller with Dynamic REFIN

Maxim Integrated 

Single Quick-PWM Step-Down

Controller with Dynamic REFIN

Pin Description

PIN

NAME

FUNCTION

Shutdown Control Input. Connect to VDD for normal operation. Pull EN low to place the controller into

1

EN

its 2μA shutdown state. When disabled, the MAX8792 slowly ramps down the target/output voltage to

ground and after the target voltage reaches 0.1V, the controller forces both DH and DL low and

enters the low-power shutdown state. Toggle EN to clear the fault-protection latch.

2

VDD

Supply Voltage Input for the DL Gate Driver. Connect to the system supply voltage (+4.5V to +5.5V).

Bypass VDD to power ground with a 1μF or greater ceramic capacitor.

Low-Side Gate Driver. DL swings from GND to VDD. The controller pulls DL high when an output

3

DL

overvoltage fault is detected, overriding any negative current-limit condition that may be present. The

MAX8792 forces DL low during VCC UVLO and REFOK lockout conditions.

4

LX

Inductor Connection. Connect LX to the switched side of the inductor as shown in Figure 1.

5

DH

High-Side Gate Driver. DH swings from LX to BST. The MAX8792 pulls DH low whenever the

controller is disabled.

6

BST

Boost Flying-Capacitor Connection. Connect to an external 0.1μF 6V capacitor as shown in Figure 1.

The MAX8792 contains an internal boost switch/diode (see Figure 2).

Switching Frequency-Setting Input. An external resistor between the input power source and TON

sets the switching period (TSW = 1/fSW) according to the following equation:

7

TON

TSW

=

CTON (RTON

+

6.5kΩ)

⎛

⎝⎜

VFB

VOUT

⎞

⎠⎟

where CTON = 16.26pF and VFB = VREFIN under normal operating conditions. If the TON current

drops below 10μA, the MAX8792 shuts down, and enters a high-impedance state.

TON is high impedance in shutdown.

Feedback Voltage-Sense Connection. Connect directly to the positive terminal of the output capacitors

8

FB

for output voltages less than 2V as shown in Figure 1. For fixed-output voltages greater than 2V,

connect REFIN to REF and use a resistive divider to set the output voltage (Figure 4). FB senses the

output voltage to determine the on-time for the high-side switching MOSFET.

Current-Limit Threshold Adjustment. The current-limit threshold is 0.05 times (1/20) the voltage at

9

ILIM

ILIM. Connect ILIM to a resistive divider (from REF) to set the current-limit threshold between 20mV

and 100mV (with 0.4V to 2V at ILIM).

External Reference Input. REFIN sets the feedback regulation voltage (VFB = VREFIN) of the MAX8792

10

REFIN

using the resistor-divider connected between REF and GND. The MAX8792 includes an internal

window comparator to detect REFIN voltage transitions, allowing the controller to blank PGOOD and

the fault protection.

11

REF

2V Reference Voltage. Bypass to analog ground using a 470pF to 10nF ceramic capacitor. The

reference can source up to 50μA for external loads.

Pulse-Skipping Control Input. This four-level input determines the mode of operation under normal

steady-state conditions and dynamic output-voltage transitions:

12

SKIP

VDD (5V) = forced-PWM operation.

REF (2V) = pulse-skipping mode with forced-PWM during transitions.

Open (3.3V)= ultrasonic mode (without forced-PWM during transitions).

GND = pulse-skipping mode (without forced-PWM during transitions).

13

VCC

5V Analog Supply Voltage. Internally connected to VDD through an internal 20Ω resistor. Bypass VCC

to analog ground using a 1μF ceramic capacitor.

10 ______________________________________________________________________________________

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