advertisement 70mΩ Protected Load Management Switch – Design Note 117
Mitchell Lee and Tim Skovmand
In an effort to conserve energy, simple shutdown schemes
are incorporated into many battery-operated circuits. Not
all circuits lend themselves to direct control, however, and
instead the supply must be turned off by a switch. The
LTC В®1477 high side switch is designed for this purpose
and includes short-circuit current limit and thermal shutdown to guard against faulty loads. Figure 1 shows a
simplified block diagram of the LTC1477.
VIN V+
D1 D2 D3 CHARGE
PUMP
ENABLE LTC1477
S2 VOUT Figure 2 shows the LTC1477 and LTC699 conjoined in an
undervoltage disconnect application. The LTC699 microprocessor supervisor disables the LTC1477 and hence the
load whenever the input voltage falls below 4.65V. An
external logic signal applied to the gate of Q1 can also
disable the LTC1477. When enabled, the LTC1477 output
ramps over a period of approximately 1ms, thereby limiting
the peak current in the load capacitor to 500mA. This
prevents glitches on the 5V source line that might otherwise affect adjacent loads.
An LT В®1301 is used in Figure 3 to boost a 3.3V or 5V input
to 12V, such as VPP for Flash memory. Although the …