Overview

The LM2587 (LM2587T-ADJ / LM2587S-ADJ) is a 5A step-up (boost), flyback, and forward converter voltage regulator IC manufactured by Texas Instruments. Part of the SIMPLE SWITCHER family, it is the higher-power upgrade to the LM2577, operating at nearly double the switching frequency (100 kHz) and featuring an internal 5.0A NPN power switch.

Operating over an input voltage range of 4.0V to 40.0V DC, the LM2587 is widely used in high-power DC-DC boost modules, isolated flyback power supplies, automotive power adapters, and battery charging step-up regulators.

Quick reference

Input Supply Voltage (VIN)4.0 V to 40.0 V DC
Output Switch Voltage (VOUT)Up to 60.0 V60.0\text{ V} DC (Internal switch rated for 65V breakdown)
Internal Switch Current5.0 A5.0\text{ A} continuous switch limit
Switching Frequency100 kHz100\text{ kHz} internal fixed oscillator
Feedback Voltage (VFB)1.23 V1.23\text{ V} reference
Available VersionsFixed 12V (LM2587-12), Fixed 15V (LM2587-15), Adjustable (LM2587-ADJ)
Special FeatureBuilt-in Soft-Start & Under-Voltage Lockout (UVLO)
PackageTO-220-5 (Through-hole) / TO-263-5 DDPAK (SMD)

Pinout (TO-220-5 Package)

Looking at the front labeled face of the 5-lead package with leads pointing down:

text
        ┌─────────────┐
        │   O   [TAB] │  (Metal Mounting Tab = GROUND / GND)
        ├─────────────┤
        │   LM2587T   │  (Front Package Face)
        └─┬─┬─┬─┬─┬───┘
          1 2 3 4 5
PinNameTypeDescription
1COMPInputFrequency Compensation Input (Connect RC+CCR_C + C_C network to GND)
2FBInputFeedback Voltage Sense Input (1.23V1.23\text{V} reference to GND)
3GNDPowerGround Reference (0 V; Connected internally to Metal Tab!)
4SWOutputInternal NPN Power Switch Collector Output (Connect to Inductor / Transformer & Schottky Diode)
5VINPowerUnregulated Supply Input (+4.0V to +40V DC)

Output Voltage Formula (Adjustable Version)

VOUT=1.23V×(1+R1R2)V_{OUT} = 1.23\text{V} \times \left(1 + \frac{R_1}{R_2}\right)

Where R1R_1 is connected between VOUT and FB, and R2R_2 is connected between FB and GND.

Common mistakes

  • Inadequate heatsink for 5A loads: Switching 5.0 A5.0\text{ A} generates significant internal heat in the TO-220 package (VSAT×5A≈4 WV_{SAT} \times 5\text{A} \approx 4\text{ W}). Bolt the package tab securely to a large metal heatsink.
  • Using undersized inductors: A 5A boost converter requires a heavy-duty toroidal power inductor rated for ≥6.0 A\ge 6.0\text{ A} saturation current to avoid magnetic core saturation.

Notes

  • LM2587 vs LM2577: LM2587 handles 5.0 A5.0\text{ A} current (vs 3.0 A3.0\text{ A} on LM2577) and operates at 100 kHz100\text{ kHz} (vs 52 kHz52\text{ kHz} on LM2577), allowing smaller inductors.

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