MAX1856EUB+ Maxim Integrated Products, MAX1856EUB+ Datasheet - Page 8

• Manufacturer Part Number: MAX1856EUB+
• Description: IC PS PWM SLIC SYNCH 10-UMAX
• Manufacturer: Maxim Integrated Products

Specifications of MAX1856EUB+

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 575kHz
• Duty Cycle: 94%
• Voltage - Supply: 3 V ~ 28 V
• Buck: No
• Boost: No
• Flyback: Yes
• Inverting: Yes
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 85°C
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Frequency-max: 575kHz
• Output Voltage: 0 V to - 185 V
• Output Current: 0.3 A
• Input Voltage: 3 V to 28 V
• Switching Frequency: 500 KHz
• Mounting Style: SMD/SMT
• Duty Cycle (max): 94 %
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX1856 current-mode PWM controller uses an
inverting flyback configuration that is ideal for generat-
ing the high negative voltages required for SLIC power
supplies. Optimum conversion efficiency is maintained
over a wide range of loads by employing both PWM
operation and Maxim’s proprietary Idle Mode control to
minimize operating current at light loads. Other features
include shutdown, adjustable internal operating fre-
quency or synchronization to an external clock, soft-
start, adjustable current limit, and a wide (3V to 28V)
input range.
The heart of the MAX1856 current-mode PWM con-
troller is a BiCMOS multi-input comparator that simulta-
neously processes the output-error signal, the
current-sense signal, and a slope-compensation ramp
(Figure 2). The main PWM comparator is direct sum-
ming, lacking a traditional error amplifier and its associ-
Wide Input Range, Synchronizable,
PWM SLIC Power Supply
8
PIN
_______________________________________________________________________________________
10
1
2
3
4
5
6
7
8
9
SYNC/SHDN
NAME
PGND
FREQ
GND
LDO
REF
V
EXT
CS
FB
CC
Detailed Description
5V Linear Regulator Output. The regulator powers all of the internal circuitry, including the EXT gate
driver. Bypass LDO to GND with a 1µF or greater ceramic capacitor.
Oscillator Frequency Set Input. A resistor from FREQ to GND sets the oscillator from 100kHz (R
500kΩ) to 500kHz (R
an external clock is connected to SYNC/SHDN.
Analog Ground
1.25V Reference Output. REF can source up to 400µA. Bypass to GND with a 2.2µF ceramic capacitor.
Feedback Input. The feedback voltage threshold is 0.
Positive Current-Sense Input. Connect a current-sense resistor (R
Power Ground
External MOSFET Gate-Driver Output. EXT swings from LDO to PGND.
Input Supply to the Linear Regulator. V
ceramic capacitor.
Shutdown Control and Synchronization Input. There are three operating modes:
• SYNC/SHDN low: shutdown mode
• SYNC/SHDN high: the DC-to-DC controller operates with the oscillator frequency set at FREQ by
• SYNC/SHDN clocked: the DC-to-DC controller operates with the oscillator frequency set by the SYNC
R
clock input. The conversion cycles initiate on the rising edge of the input clock signal. However, the
MAX1856 still requires R
OSC
PWM Controller
OSC
= 100kΩ): f
OSC
when SYNC/SHDN is externally clocked.
OSC
CC
ated phase shift. The direct-summing configuration
approaches ideal cycle-by-cycle control over the out-
put voltage since there is no conventional error amplifi-
er in the feedback path.
In PWM mode, the controller uses fixed-frequency, cur-
rent-mode operation where the duty ratio is set by the
input-to-output voltage ratio and the transformer’s turn
ratio. The current-mode feedback loop regulates peak
inductor current as a function of the output error signal.
At light loads, the controller enters Idle Mode. During
Idle Mode, switching pulses are provided only as nec-
essary to supply the load, and operating current is min-
imized to provide the best light-load efficiency. The
minimum-current comparator threshold is 15mV, or
15% of the full-load value (I
controller is synchronized to an external clock, Idle
Mode occurs only at very light loads.
= 50MΩ-kHz / R
accepts inputs up to 28V. Bypass to PGND with a 1µF
FUNCTION
OSC
. The MAX1856 still requires R
CS
) between CS and PGND.
MAX
Pin Description
) of 100mV. When the
OSC
OSC
when
=