Pin description – Rainbow Electronics MAX1847 User Manual
Page 8
MAX1846/MAX1847
High-Efficiency, Current-Mode,
Inverting PWM Controller
8
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Pin Description
PIN
MAX1846
MAX1847
NAME
FUNCTION
—
1
POL
Sets polarity of the EXT pin. Connect POL to GND to set EXT for use with an external
PMOS high-side FET. Connect POL to VL to set EXT for use with an external NMOS low-
side FET in transformer-based applications.
1
2
VL
VL Low-Dropout Regulator. Connect 0.47µF ceramic capacitor from VL to GND.
2
3
FREQ
Oscillator Frequency Set Input. Connect a resistor (R
FREQ
) from FREQ to GND to set the
internal oscillator frequency from 100kHz (R
FREQ
= 500k
Ω) to 500kHz (R
FREQ
= 76.8k
Ω).
R
FREQ
is still required if an external clock is used at SYNC. See Setting the Operating
Frequency section.
3
4
COMP
Compensation Node for Error Amp/Integrator. Connect a series resistor/capacitor network
from COMP to GND for loop compensation. See Design Procedure.
4
5
REF
1.25V Reference Output. REF can source up to 500µA. Bypass with a 0.1µF ceramic
capacitor from REF to GND.
5
6
FB
Feedback Input. Connect FB to the center of a resistor-divider connected between the
output and REF. The FB threshold is 0.
—
7,9
N.C.
No Connection
—
8
SHDN
Shutdown Control. Drive SHDN low to turn off the DC-DC controller. Drive high or connect
to IN for normal operation.
6
10,11
GND
Analog Ground. Connect to PGND.
7
12
PGND
Negative Rail for EXT Driver and Negative Current-Sense Input. Connect to GND.
8
13
CS
P osi ti ve C ur r ent- S ense Inp ut. C onnect a cur r ent- sense r esi stor ( R
C S
) b etw een C S and
9
14
EXT
External MOSFET Gate-Driver Output. EXT swings from IN to PGND.
10
15
IN
Power-Supply Input
—
16
SYNC
Operating Frequency Synchronization Control. Drive SYNC low or connect to GND to set
the internal oscillator frequency with R
FREQ
. Drive SYNC with a logic-level clock input
signal to externally set the converter’s operating frequency. DC-DC conversion cycles
initiate on the rising edge of the input clock signal. Note that when driving SYNC with an
external signal, R
FREQ
must still be connected to FREQ.