Datasheet

Detailed Description
The MAX5090 step-down DC-DC converter operates from
a 6.5V to 76V input voltage range. A unique voltage-mode
control scheme with voltage feed-forward and an internal
switching DMOS FET provides high efficiency over a wide
input voltage range. This pulse-width-modulated convert-
er operates at a fixed 127kHz switching frequency or can
be synchronized with an external system clock frequency.
The device also features automatic pulse-skipping mode
to provide high efficiency at light loads. Under no load,
the MAX5090 consumes only 310µA, and in shutdown
mode, consumes only 20µA. The MAX5090 also features
undervoltage-lockout, hiccup-mode output short-circuit
protection and thermal shutdown.
ON/OFF/Undervoltage Lockout (UVLO)
Use the ON/OFF function to program the external UVLO
threshold at the input. Connect a resistive voltage-divider
from V
IN
to SGND with the center node to ON/OFF, as
shown in Figure 1. Calculate the threshold value by using
the following formula:
UVLO(TH)
R1
V 1 1.38
R2

=+×


Set the external V
UVLO(TH)
to greater than 6.45V. The
maximum recommended value for R2 is less than 1MΩ.
ON/OFF is a logic input and can be safely driven to the full
V
IN
range. Connect ON/OFF to V
IN
for automatic startup.
Drive ON/OFF to ground to shut down the MAX5090.
Shutdown forces the internal power MOSFET off, turns off
all internal circuitry, and reduces the V
IN
supply current to
20µA (typ). The ON/OFF rising threshold is 1.546V (max).
Before any operation begins, the voltage at ON/OFF must
exceed 1.546V. The ON/OFF input has 100mV hysteresis.
If the external UVLO threshold-setting divider is not used,
an internal undervoltage-lockout feature monitors the
supply voltage at V
IN
and allows the operation to start
when V
IN
rises above 6.45V (max). The internal UVLO
rising threshold is set at 6.17V with 0.5V hysteresis.
The V
IN
and V
ON/OFF
voltages must be above 6.5V and
1.546V, respectively, for proper operation.
PIN NAME FUNCTION
1, 2 LX Source Connection of Internal High-Side Switch
3 BST Boost Capacitor Connection. Connect a 0.22µF ceramic capacitor from BST to LX.
4 V
IN
Input Voltage. Bypass V
IN
to SGND with a low-ESR capacitor as close as possible to the device.
5 VD Internal Regulator Output. Bypass VD to PGND with a 3.3µF/10V or greater ceramic capacitor.
6 SYNC
Synchronization Input. Connect SYNC to an external clock for synchronization. Connect to SGND to
select the internal 127kHz switching frequency.
7 SS
Soft-Start Capacitor Connection. Connect an external capacitor from SS to SGND to adjust the
soft-start time.
8 FB
Output Sense Feedback Connection.
For xed output voltage (MAX5090A/MAX5090B), connect FB to V
OUT
.
For adjustable output voltage (MAX5090C), use an external resistive voltage-divider to set V
OUT
.
V
FB
regulating set point is 1.228V.
9 ON/OFF
Shutdown Control Input. Pull ON/OFF low to put the device in shutdown mode. Drive ON/OFF high for
normal operation. Connect ON/OFF to V
IN
with short leads for always-on operation.
10 SGND Signal Ground. SGND must be connected to PGND for proper operation.
11, 15, 16 N.C. No Connection. Not internally connected.
12 PGND Power Ground
13, 14 DRAIN Internal High-Side Switch Drain Connection
— EP
Exposed Pad. Solder EP to SGND plane to aid in heat dissipation. Do not use as the only electrical
ground connection.
MAX5090A/B/C 2A, 76V, High-Efciency MAXPower
Step-Down DC-DC Converters
www.maximintegrated.com
Maxim Integrated │ 7
Pin Description