MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
10 ______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1EN
Shutdown Control Input. Connect to V
DD
for normal operation. Pull EN low to place the controller into
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.
2V
DD
Supply Voltage Input for the DL Gate Driver. Connect to the system supply voltage (+4.5V to +5.5V).
Bypass V
DD
to power ground with a 1μF or greater ceramic capacitor.
3DL
Low-Side Gate Driver. DL swings from GND to V
DD
. The controller pulls DL high when an output
overvoltage fault is detected, overriding any negative current-limit condition that may be present. The
MAX8792 forces DL low during V
CC
UVLO and REFOK lockout conditions.
4 LX Inductor Connection. Connect LX to the switched side of the inductor as shown in Figure 1.
5DH
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).
7TON
Switching Frequency-Setting Input. An external resistor between the input power source and TON
sets the switching period (T
SW
= 1/f
SW
) according to the following equation:
where C
TON
= 16.26pF and V
FB
= V
REFIN
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.
8FB
Feed b ack V ol tag e- S ense C onnecti on. C onnect d i r ectl y to the p osi ti ve ter m i nal of the outp ut cap aci tor s
for outp ut vol tag es l ess than 2V as show n i n Fi g ur e 1. For fi xed - outp ut vol tag es g r eater than 2V ,
connect RE FIN to RE F and use a r esi sti ve d i vi d er to set the outp ut vol tag e ( Fi g ur e 4) . FB senses the
outp ut vol tag e to d eter m i ne the on- ti m e for the hi g h- si d e sw i tchi ng M OS FE T.
9 ILIM
Current-Limit Threshold Adjustment. The current-limit threshold is 0.05 times (1/20) the voltage at
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).
10 REFIN
External Reference Input. REFIN sets the feedback regulation voltage (V
FB
= V
REFIN
) of the MAX8792
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.
12 SKIP
Pulse-Skipping Control Input. This four-level input determines the mode of operation under normal
steady-state conditions and dynamic output-voltage transitions:
V
DD
(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 V
CC
5V Analog Supply Voltage. Internally connected to V
DD
through an internal 20Ω resistor. Bypass V
CC
to analog ground using a 1μF ceramic capacitor.
TCR k
V
V
SW TON TON
FB
OUT
=+
()
⎛
⎝
⎜
⎞
⎠
⎟
65. Ω
