Rainbow Electronics MAX5953D - Manual (Page 11)

MAX5953A/MAX5953B/MAX5953C/MAX5953D
IEEE 802.3af PD Interface and PWM Controllers
with Integrated Power MOSFETs
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Pin Description (continued)
PIN NAME FUNCTION
25 OPTO
PWM Comparator Inverting Input. OPTO is referenced to GND. Connect the collector of the
optotransistor to OPTO and a pullup resistor to REGOUT.
26, 27 SRC
Source Connection of Low-Side Power MOSFET in the Two-Switch Power Stage of the DC-
DC Converter. Connect SRC to PGND with a low-value resistor for current limiting.
28, 29 XFRMRL
Low-Side Connection for the Isolation Transformer. Drain terminal of low-side power
MOSFET in the two-switch power stage of the DC-DC converter.
30 DRVIN
Supply Input for the Gate-Driver of Internal Power MOSFETs. DRVIN is referenced to
PGND. Bypass DRVIN with at least 0.1µF to PGND. Connect DRVIN to REGOUT.
31, 32 XFRMRH
High-Side Connection for the Isolation Transformer. Source connection of high-side power
MOSFET in the two-switch power stage of the DC-DC converter.
33, 34 DRNH
Drain Connection of High-Side MOSFET in the Two-Switch Power Stage of the DC-DC
Converter. Connect DRNH to the most positive rail of the input supply. Bypass DRNH
appropriately to handle the heavy switching current through the transformer.
36 BST
Boost Input for the DC-DC Converter. BST is the boost connection point for the high-side
MOSFET driver. Connect a minimum 0.1µF capacitor from BST to XFRMRH with short and
wide PC board traces.
37 DCUVLO
DC-DC Converter Undervoltage Lockout Input. DCUVLO is referenced to GND. Connect a
resistor-divider from HVIN to DCUVLO to GND to set the UVLO threshold.
39 HVIN
DC-DC Converter Positive Input Power Supply. HVIN is referenced to GND. Connect HVIN
to V+.
40 INBIAS
Input from the Rectified Bias Winding to the DC-DC Converter. INBIAS is referenced to
GND. INBIAS is the input to the internal linear voltage regulator (REGOUT).
41 REGOUT
Internal Regulator Output. REGOUT is used for the DC-DC converter gate driver. REGOUT
is referenced to GND. V
REGOUT is always present as long as HVIN is powered with a
voltage above the DCUVLO threshold. Bypass REGOUT to GND with a minimum 2.2µF
ceramic capacitor.
42 RTCT
Oscillator Frequency Set Input for the PWM Controller. RTCT is referenced to GND.
Connect a resistor from RTCT to REGOUT and a ceramic capacitor from RTCT to GND to
set the oscillator frequency.
43 FLTINT
Fault Integration Input for PWM Controller. FLTINT is referenced to GND. During persistent
current-limit faults, a capacitor connected to FLTINT is charged with an internal 80µA
current source. Switching is terminated when V
FLTINT reaches 2.7V. An external resistor
connected in parallel discharges the capacitor. Switching resumes when V FLTINT drops
to 1.9V.
44 RCFF
Feed-Forward Input for PWM Controller. RCFF is referenced to GND. To generate the PWM
ramp, connect a resistor from RCFF to HVIN and a capacitor from RCFF to GND.
45 RAMP Ramp Sense Input for PWM Controller. Connect RAMP to RCFF.
— EP
Exposed Paddle. EP is internally unconnected and must be connected to V EE externally.
To improve power dissipation, solder the exposed paddle to a copper pad on the PC
board.