SMH4804 Datasheet, PDF (6/41 Pages) Summit Microelectronics, Inc. – -48V Programmable Hot Swap Sequencing Power Controller

Functional Description
SMH4804
Circuit Breaker Operation
The SMH4804 provides a number of circuit breaker
functions to protect against over-current conditions. A
sustained over-current event could damage the host supply
and/or the load circuitry. The board’s load current passes
through a series resistor (R_S) connected between the
MOSFET source (which is tied to CBSENSE) and V_SS. The
breaker trips whenever the voltage drop across R_S is
greater than 50mV for more than t_CBD (a programmable
filter delay ranging from 10µs to 500µs).
The circuit breaker cycle time is controlled via bit 0 of
Register 4.
Figure 5 shows the circuit breaker duty cycle operation with
RESET# high.
CBSENSE
T_{CBD 50mV}
T_CBD
VGATE
T_CYC
2050 Fig03 1.0
Figure 5. Circuit Breaker Duty Cycle Operation with
RESET# High
Figure 6 shows the behavior of VGATE and CBSENSE
immediately after RESET# is deasserted.
The circuit breaker cycle time can be programmed to a
value of either 2.5 seconds of 5 seconds depending on the
system configuration. Refer to bit 0 of Register 4 - Address
0100 on page 33 for more information on selecting the
circuit breaker cycle time.
CBSENSE
T_CBD
50mV
VGATE
T_PDD
T_CBRST
RESET#
2050 Fig04 2.1
Figure 6. Circuit Breaker Reset with RESET# Low
Quick-Trip^TM Circuit Breaker
The SMH4804 provides a Quick-Trip™ feature that causes
the circuit breaker to trip immediately if the voltage drop
across 5₆ exceeds V_QCB. The Quick-Trip level may be set
to 60mV, 100mV (default), 200mV, or the feature may be
disabled. Refer to bits 1:0 of Register 2 - Address 0010 on
page 31 for more information.
Figure 7 shows the circuit breaker ‘Quick Trip’ response.In
this figure, the voltage rises above V_QCB, causing VGATE to
be deasserted.
CBSENSE
<T_CBD
V_QCB
50mV
VGATE
T_FSTSHTDN
2050 Fig05 2.0
Figure 7. Circuit Breaker Quick Trip Response
Current Regulation
The current regulation mode is an optional feature that
provides a means to regulate current through the MOSFET
for a programmable period of time using bits 1:0 of Register
6.
6
2050 3.7 10/30/02
Summit Microelectronics