ER3110DI Datasheet, PDF (16/23 Pages) Altera Corporation – Synchronous Buck Regulator

Page 16
The output voltage programming resistor, R₃, depends on the value chosen for the feedback resistor, R₂, and the
desired output voltage, V_OUT, of the regulator. Equation 3 describes the relationship between V_OUT and resistor values.
R₃ = -V---_O-R---_U-²--_T-x---0_–---.--60---.V-6----V--
(EQ. 3)
If the desired output voltage is 0.6V, then R₃ is left unpopulated and R₂ is 0?.
R₂
FB
V_OUT
EA
R₃
0.6V
REFERENCE
FIGURE 45. EXTERNAL RESISTOR DIVIDER
Protection Features
The ER3110DI is protected from overcurrent, negative overcurrent and over-temperature. The protection circuits
operate automatically.
Overcurrent Protection
During PWM on-time, current through the upper FET is monitored and compared to a nominal 1.5A peak overcurrent
limit. In the event that current reaches the limit, the upper FET will be turned off until the next switching cycle. In this
way, FET peak current is always well limited.
If the overcurrent condition persists for 17 sequential clock cycles, the regulator will begin its hiccup sequence. In this
case, both FETS will be turned off and POK will be pulled low. This condition will be maintained for 8 soft-start
periods after which the regulator will attempt a normal soft-start.
Should the output fault persist, the regulator will repeat the hiccup sequence indefinitely. There is no danger even if
the output is shorted during soft-start.
If V_OUT is shorted very quickly, FB may collapse below 5/8^ths of its target value before 17 cycles of overcurrent are
detected. The ER3110DI recognizes this condition and will begin to lower its switching frequency proportional to the
FB pin voltage. This insures that under no circumstance (even with V_OUT near 0V) will the inductor current run away.
Negative Current Limit
Should an external source somehow drive current into V_OUT, the controller will attempt to regulate V_OUT by reversing its
inductor current to absorb the externally sourced current. In the event that the external source is low impedance, current
may be reversed to unacceptable levels and the controller will initiate its negative current limit protection. Similar to
normal overcurrent, the negative current protection is realized by monitoring the current through the lower FET. When
the valley point of the inductor current reaches negative current limit, the lower FET is turned off and the upper FET is
forced on until current reaches the POSITIVE current limit or an internal clock signal is issued. At this point, the lower
FET is allowed to operate. Should the current again be pulled to the negative limit on the next cycle, the upper FET will
again be forced on and current will be forced to 1/6^th of the positive current limit. At this point the controller will turn off
both FET’s and wait for COMP to indicate return to normal operation. During this time, the controller will apply a 100Ω
load from SW to PGND and attempt to discharge the output. Negative current limit is a pulse-by-pulse style operation
and recovery is automatic.
Over-Temperature Protection
Over-temperature protection limits maximum junction temperature in the ER3110DI. When junction temperature (T_J)
exceeds +150°C, both FETs are turned off and the controller waits for temperature to decrease by approximately 20°C.
During this time POK is pulled low. When temperature is within an acceptable range, the controller will initiate a
normal soft-start sequence. For continuous operation, the +125°C junction temperature rating should not be exceeded.
Enpirion Power Datasheet ER3110DI Wide PVIN 1A Synchronous Buck Regulator
10038
May 28, 2014
May 2014 Altera Corporation
Rev A