MIC28500 Datasheet, PDF (21/29 Pages) Micrel Semiconductor – 75V/4A Hyper Speed Control™ Synchronous DC-DC Buck Regulator

Micrel, Inc.
grease or thermal glue to make sure that the thermal
couple junction is making good contact with the case of
the IC. Omega brand thermal couple (5SC-TT-K-36-36)
is adequate for most applications.
Wherever possible, an infrared thermometer is
recommended. The measurement spot size of most
infrared thermometers is too large for an accurate
reading on a small form factor ICs. However, a IR
thermometer from Optris has a 1mm spot size, which
makes it a good choice for measuring the hottest point
on the case. An optional stand makes it easy to hold the
beam on the IC for long periods of time.
External V_IN Limiter Circuit
The external V_IN limiter circuit can be implemented either
on EN pin or VDD pin. Only one of these V_IN limiter
circuits is required. The external V_IN limiter circuit limits
the minimum input to 30V. If the minimum input in
certain applications is more than 30V then neither of
these limiter circuits is needed. Enabling the device
below 30V VIN and under maximum loading could heat
up the device beyond safe operating conditions. The
following figures show the external V_IN limiter circuit on
EN and VDD pins Figure 9A and Figure 9B respectively.
The V_IN limiter on EN consists of D5, R22, D6, R23 and
V_IN limiter on the VDD pin along with VDD supply
regulator consists of D4, R14, D2, and Q1.
MIC28500
Figure 9B: V_IN Limiter On VDD pin
Figure 9A: V_IN Limiter On EN pin
June 2011
21
M9999-060311-B