Rainbow Electronics MAX5081 - Manual (Page 9)

MAX5080/MAX5081
1A, 40V, MAXPower Step-Down
DC-DC Converters
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Internal Linear Regulator (REG)
REG is the output terminal of a 5V (MAX5080), or 8V
(MAX5081) LDO which is powered from IN and pro-
vides power to the IC. Connect REG externally to
DVREG to provide power for the high-side MOSFET
gate driver. Bypass REG to SGND with a ceramic
capacitor of at least 1µF. Place the capacitor physically
close to the MAX5080/MAX5081 to provide good
bypassing. During normal operation, REG is intended
for powering up only the internal circuitry and should
not be used to supply power to external loads.
Internal UVLO/External UVLO
The MAX5080/MAX5081 provides two undervoltage
lockouts (UVLOs). An internal UVLO looks at the input
voltage (V
IN ) and is fixed at 4.1V (MAX5080) or 7.1V
(MAX5081). An external UVLO is sensed and pro-
grammed at the ON/OFF pin. The external UVLO over-
rides the internal UVLO when the external UVLO is
higher than the internal UVLO. During startup, before
any operation begins, the input voltage and the voltage
at ON/OFF must exceed their respective UVLOs. The
external UVLO has a rising threshold of 1.23V with
0.12V of hysteresis. Program the external UVLO by
connecting a resistive divider from IN to ON/OFF to
SGND. Connect ON/OFF to IN directly to disable the
external UVLO.
Driving ON/OFF to ground places the MAX5080/
MAX5081 in shutdown. When in shutdown the internal
power MOSFET turns off, all internal circuitry shuts
down and the quiescent supply current reduces to
200µA. Connect an RC network from ON/OFF to SGND
to set a turn-on delay that can be used to sequence the
output voltages of multiple devices.
MAX5080
1.23V
1.23V
ON/OFF
DVREG
PCLK
LDO
EN
IN
REG
SS
FB
THERMAL
SHDN
REF
IN
0.3V
CLK
1.23V
REGOK
EN
V REF
V REF
I
SS
>1.23V ON
<1.11V OFF
COMP
SYNC
E/A SSA
CPWM
RAMP
LOGIC
EN
OSC
CHARGE-PUMP
MANAGEMENT
PCLK
BST
IN
SGND
LX
PGND
SCLK
HIGH-SIDE
CURRENT
SENSE
REF_PFM
PFM
REF_ILIM
ILIM
OVERL
CLK
ILIM OVERLOAD
MANAGEMENT
DVREG C+
DVREG
C-
LEVEL
SHIFT
Figure 1. MAX5080 Simplified Block Diagram